Water and nitrogen （N） inputs are considered as the two main limiting factors affecting plant growth.Changes in these inputs are expected to alter the structure and composition of the plant community,thereby influen...Water and nitrogen （N） inputs are considered as the two main limiting factors affecting plant growth.Changes in these inputs are expected to alter the structure and composition of the plant community,thereby influencing biodiversity and ecosystem function.Snowfall is a form of precipitation in winter,and snow melting can recharge soil water and result in a flourish of ephemerals during springtime in the Gurbantunggut Desert,China.A bi-factor experiment was designed and deployed during the snow-covering season from 2009 to 2010.The experiment aimed to explore the effects of different snow-covering depths and N addition levels on ephemerals.Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast,N addition sharply decreased the density of ephemerals in the same snow treatment.Meanwhile,N addition exhibited a different effect on the growth of ephemeral plants：in the 50％ snow treatment,N addition limited the growth of ephemeral plants,showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth （100％ and 150％ snow treatments）,N addition benefited the growth of the dominant individual plants.Species richness was not significantly affected by snow in the same N treatment.However,N addition significantly decreased the species richness in the same snow-covering depth.The primary productivity of ephemerals in the N addition increased with the increase of snow depth.These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply.With plenty of water （100％ and 150％ snow treatments）,N addition contributed to the growth of ephemeral plants; while with less water （50％ snow treatment）,N addition restricted the growth of ephemeral plants.展开更多
Nitrogen(N)addition has profound impacts on litter-mediated nutrient cycling.Numerous studies have reported different effects of N addition on litter decomposition,exhibiting positive,negative,or neutral effects.Previ...Nitrogen(N)addition has profound impacts on litter-mediated nutrient cycling.Numerous studies have reported different effects of N addition on litter decomposition,exhibiting positive,negative,or neutral effects.Previous meta-analysis of litter decomposition under N addition was mainly based on a small number of samples to allow comparisons among ecosystem types.This study presents the results of a meta-analysis incorporating data from 53 published studies(including 617 observations)across forests,grasslands,wetlands,and croplands in China,to investigate how environmental and experimental factors impact the effects of N addition on litter decomposition.Averaged across all of the studies,N addition significantly slows litter decomposition by 7.02%.Considering ecosystem types,N addition significantly accelerates litter decomposition by 3.70%and 11.22%in grasslands and wetlands,respectively,clearly inhibits litter decomposition by 14.53%in forests,and has no significant effects on litter decomposition in croplands.Regarding the accelerated litter decomposition rate in grasslands due to N addition,litter decomposition rate increases slightly with increasing rates of N addition.However,N addition slows litter decomposition in forests,but litter decomposition is at a significantly increasing rate with increasing amounts of N addition.The responses of litter decomposition to N addition are also influenced by the forms of N addition,experiential duration of N addition,humidity index,litter quality,and soil pH.In summary,N addition alters litter decomposition rate,but the direction and magnitude of the response are affected by the forms of N addition,the rate of N addition,ambient N deposition,experimental duration,and climate factors.Our study highlights the contrasting effects of N addition on litter decomposition in forests and grasslands.This finding could be used in biogeochemical models to better evaluate ecosystem carbon cycling under increasing N deposition due to the differential responses of litter decomposition to N addition rates and ecosystem types.展开更多
During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three differ...During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition;N15: 1.5 g N/m<sup>2</sup>·a;N30: 3.0 g N/m<sup>2</sup>·a;N50: 5.0 g N/m<sup>2</sup>·a;N100: 10.0 g N/m<sup>2</sup>·a;N150: 15.0 g N/m<sup>2</sup>·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.展开更多
Background:The nitrogen isotope natural abundance(δ^(15)N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ^(13)C)has been used to infer how water-using processes of plan...Background:The nitrogen isotope natural abundance(δ^(15)N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ^(13)C)has been used to infer how water-using processes of plants change in terrestrial ecosystems.However,howδ^(13)C andδ^(15)N abundances in plant life and soils respond to N addition and water availability change is still unclear.Thus,δ^(13)C andδ^(15)N abundances in plant life and soils were used to investigate the effects of long-time(10 years)N addition(+50 kg N·ha^(−1)·yr^(−1)and precipitation reduction(−30%of throughfall)in forest C and N cycling traits in a temperate forest in northern China.Results:We analyzed theδ^(13)C andδ^(15)N values of dominant plant foliage,litterfall,fungal sporophores,roots,and soils in the study.The results showed thatδ^(15)N values of foliage,litterfall,and surface soil layer’s(0–10 cm)total N were significantly increased by N addition,whileδ^(15)N values of fine roots and coarse roots were considerably decreased.Nitrogen addition also significantly increased theδ^(13)C value of fine roots and total N concentration of the surface soil layer compared with the control.The C concentration,δ^(13)C,andδ^(15)N values of foliage andδ^(15)N values of fine roots were significantly increased by precipitation reduction,while N concentration of foliage and litterfall significantly decreased.The combined effects of N addition and precipitation reduction significantly increased theδ^(13)C andδ^(15)N values of foliage as well as theδ^(15)N values of fine roots andδ^(13)C values of litterfall.Furthermore,foliarδ^(15)N values were significantly correlated with foliageδ^(13)C values,surface soilδ^(15)N values,surface soil C concentration,and N concentrations.Nitrogen concentrations andδ^(13)C values of foliage were significantly correlated withδ^(15)N values and N concentrations of fine roots.Conclusions:This indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction,suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.展开更多
Understanding how the growth of two key native grass species of the Northern Great Plains （Western wheatgrass and blue grama） may be affected under drought and nitrogen deficiency is essential for future management ...Understanding how the growth of two key native grass species of the Northern Great Plains （Western wheatgrass and blue grama） may be affected under drought and nitrogen deficiency is essential for future management of these grasslands. The random complete block experimental design greenhouse study examined the effects of water and N addition on above-ground and below-ground harvested biomass of C3 （Western wheatgrass, WWG） and C4 （blue grama, BG） grass species for the purpose of gaining better understanding of drought responses for these two species. Compared with well-watered treatment （field capacity）, two water limited treatments （70% and 85% field capacity） decreased plant above- and below-ground biomass （WWG and BG）. For two N treatments （no N added, addition of 100 mg N kg^-1soil）, addition of N significantly improved plant above- and below-ground biomass of WWG and BG under water field capacity. Both above- and below-ground biomass of the two grass species increased linearly with increasing water supplied, but above- and below-ground biomass of WWG was always lower than BG for the same treatments （water or N addition）. The results demonstrated that BG seedlings had better adaptation than WWG to deal with the imposed drought or N deficient conditions.展开更多
Background Changes in soil greenhouse gas(GHG)fluxes caused by nitrogen(N)addition are considered as the key factors contributing to global climate change(global warming and altered precipitation regimes),which in tur...Background Changes in soil greenhouse gas(GHG)fluxes caused by nitrogen(N)addition are considered as the key factors contributing to global climate change(global warming and altered precipitation regimes),which in turn alters the feedback between N addition and soil GHG fluxes.However,the effects of N addition on soil GHG emissions under climate change are highly variable and context-dependent,so that further syntheses are required.Here,a meta-analysis of the interactive effects of N addition and climate change(warming and altered precipitation)on the fluxes of three main soil GHGs[carbon dioxide(CO_(2)),methane(CH_(4)),and nitrous oxide(N_(2)O)]was conducted by synthesizing 2103 observations retrieved from 57 peer-reviewed articles on multiple terrestrial ecosystems globally.Results The interactive effects of N addition and climate change on GHG fluxes were generally additive.The combination of N addition and warming or altered precipitation increased N_(2)O emissions significantly while it had minimal effects on CO_(2)emissions and CH_(4)uptake,and the effects on CH_(4)emissions could not be evaluated.Moreover,the magnitude of the combined effects did not differ significantly from the effects of N addition alone.Apparently,the combined effects on CO_(2)and CH_(4)varied among ecosystem types due to differences in soil moisture,which was in contrast to the soil N_(2)O emission responses.The soil GHG flux responses to combined N addition and climate change also varied among different climatic conditions and experimental methods.Conclusion Overall,our findings indicate that the effects of N addition and climate change on soil GHG fluxes were relatively independent,i.e.combined effects of N addition and climate change were equal to or not significantly different from the sum of their respective individual effects.The effects of N addition on soil GHG fluxes influence the feedbacks between climate change and soil GHG fluxes.展开更多
Atmospheric nitrogen （N） deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon （C） sequestration in an ecosystem. Using the litt...Atmospheric nitrogen （N） deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon （C） sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition （CK： no N addition; low-N： 1 g N m-2 y-l; high-N： 2 g N m-2 y-l） on changes in mass remaining of shoot litter decomposition of three grasses （Stipa baicalensis, Carex pediformis and Leymus chinensis） over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition.展开更多
Aims Better understanding of microbial compositional and physiological acclimation mechanisms is critical for predicting terrestrial ecosystem responses to global change.The aim is to assess variations in soil microbi...Aims Better understanding of microbial compositional and physiological acclimation mechanisms is critical for predicting terrestrial ecosystem responses to global change.The aim is to assess variations in soil microbial communities under future scenarios of changing precipitation and N deposition in a semiarid grassland of northern China.Methods In order to explicitly estimate microbial responses,a field experiment with water and N addition was established in April 2005 and continuously conducted for 4 years.Specifically,soil microbial community composition and microbial C utilization potential were determined by phospholipid fatty acid(PLFA)and community-level physiological profiles,respectively.Important Findings Water addition had no effects on the PLFA concentrations of grampositive(GP)and negative bacteria(GN),total bacteria and fungi.However,N addition caused significant reductions in the PLFA concentrations of GP,GN,total bacteria and fungi and thus decreased total PLFA of microbial communities.Moreover,there were interactive effects of water and N addition on GN/GPand the ratio of fungal to bacterial PLFA(F/B).In addition,synergistic effects were found between water and nitrogen in affecting microbial C utilization potentials,which implies that microbial C utilization potentials tend to be enhanced when both N and water availability are sufficient.Overall,the microbial responses to water and N addition support our hypothesis that water and N addition may be combined together to affect microbial communities in the semiarid grassland.展开更多
Aims Leaf nutrient resorption is sensitive to changes in soil nutrients.However,the effects of N deposition on nutrient resorption efficiency(NuRE)in plant macro-nutrients remain unclear.Poplar(Populus deltoids)is one...Aims Leaf nutrient resorption is sensitive to changes in soil nutrients.However,the effects of N deposition on nutrient resorption efficiency(NuRE)in plant macro-nutrients remain unclear.Poplar(Populus deltoids)is one of the most extensively cultivated hardwood species worldwide.We explored general patterns and dominant drivers of NuRE and stoichiometry of poplar plantations in response to N addition.Methods We conducted a 4-year N-addition experiment to explore NuRE and stoichiometric responses to N addition in two poplar(P.deltoids)plantations(8-and 12-year-old stands)in a coastal region of eastern China.We measured soil and foliar(green and senesced leaves)concentrations of nitrogen(N),phosphorus(P),potassium(K),calcium(Ca)and magnesium(Mg)for a series of N addition treatments including N_(0)(0 kg N ha^(−1)yr^(−1)),N_(1)(50 kg N ha^(−1)yr^(−1)),N_(2)(100 kg N ha^(−1)yr^(−1)),N_(3)(150 kg N ha^(−1)yr^(−1))and N_(4)(300 kg N ha^(−1)yr^(−1)).Important Findings Consistent for(both)8-and 12-year-old stands,N addition did not affect the NuRE and stoichiometry(with the exception of CaRE and CaRE:MgRE ratio).N resorption efficiency–P resorption efficiency(NRE–PRE)scaling slopes were consistently less than 1.0 under N addition.These results suggest that NRE generally decouples from PRE within each N treatment.Moreover,these results point to robust control of green leaf nutritional status on nutrient resorption processes as indicated by the positive relationships between NuRE and green leaf nutrient concentrations.Our findings provided a direct evidence that growth in 12-year-old poplar plantations was N-limited in the coastal region of eastern China.展开更多
Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to ...Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands,how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood.Therefore,we conducted an N and P addition experiment(involving control,N addition,P addition,and N+P addition)in an alpine grassland on Kunlun Mountains(Xinjiang Uygur Autonomous Region,China)in 2016 and 2017 to investigate the changes in leaf nutrient concentrations(i.e.,leaf N,Leaf P,and leaf N:P ratio)and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata,which are dominant species in this grassland.Results showed that N addition has significant effects on soil inorganic N(NO_(3)^(-)-N and NH_(4)^(+)-N)and leaf N of both species in the study periods.Compared with green leaves,leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S.rhodanthum was more sensitive to N addition,whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S.capillata.N addition did not influence N resorption efficiency of the two species.P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period.These influences on plants can be explained by increasing P availability.The present results illustrated that the two species are more sensitive to P addition than N addition,which implies that P is the major limiting factor in the studied alpine grassland ecosystem.In addition,an interactive effect of N+P addition was only discernable with respect to soil availability,but did not affect plants.Therefore,exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.展开更多
Aims The productivity of forest plantations in temperate areas is often lim-ited by nitrogen(N),but may shift towards phosphorus(P)limitation with increasing atmospheric N deposition.Nutrient resorption is a nutrient ...Aims The productivity of forest plantations in temperate areas is often lim-ited by nitrogen(N),but may shift towards phosphorus(P)limitation with increasing atmospheric N deposition.Nutrient resorption is a nutrient conservation strategy in plants.Although data on nutrient resorption are available for overstory trees,there are few data for understory vegetation.Methods We examined leaf N and P concentrations and N and P resorption efficiencies(NRE and PRE,respectively)in eight understory species in 11-and 45-year-old Larix principis-rupprechtii stands subjected to N supplementation over a 3-year period.Important findings Leaf N concentrations and N:P ratios increased and P concentrations decreased,with N input in species within the 45-year-old stand,but not in the 11-year-old stand.NRE and PRE were not altered by N input in any of the species in either stand,but N resorption pro-ficiency decreased and P resorption proficiency increased,in the species in the 45-year-old stand.Thus,the growth of understory species may be more P-limited in the 45-versus 11-year-old stand,and nutrient resorption proficiency was more sensitive to N add-ition than nutrient resorption efficiency.These results will improve the understanding of nutrient use strategies and their responses to N addition in understory vegetation.The contrasting effects of N addition on nutrient status between stand ages cannot be ignored when modeling ecosystem nutrient cycling under global N depos-ition conditions.展开更多
Aims We aimed to evaluate the changes in water-use efficiency(WuE)in native tree species in forests of subtropical China,and determine how coexisting species would be responding to increases in atmospheric carbon diox...Aims We aimed to evaluate the changes in water-use efficiency(WuE)in native tree species in forests of subtropical China,and determine how coexisting species would be responding to increases in atmospheric carbon dioxide(CO_(2))concentrations and nitrogen(N)deposition.Methods We used model forest ecosystems in open-top chambers to study the effects of elevated CO_(2)(ca.700μmol mol−1)alone and together with N addition(NH4No3 applied at 100 kg N ha−1year−1)on WuE of four native tree species(Schima superba,Ormosia pin-nata,Castanopsis hystrix and Acmena acuminatissima)from 2006 to 2010.Important findingsour result indicated that all species increased their WuE when they were exposed to elevated CO_(2).although higher WuE was shown in faster-growing species(S.superba and O.pinnata)than that of slower-growing species(C.hystrix and Acmena acuminatissima),the increased extent of WuE induced by elevated CO_(2) was higher in the slower-growing species than that of the faster-growing species(P<0.01).the N treatment decreased WuE of S.superba,while the effects on other species were not significant.the interactions between elevated CO_(2) and N addition increased intrinsic WuE of S.superba significantly(P<0.001),however,it did not affect WuE of the other tree species significantly.We conclude that the responses of native tree species to elevated CO_(2) and N addition are different in subtropical China.the species-specific effects of elevated CO_(2) and N addition on WuE would have important implications on species composition in China’s subtropics in response to global change.展开更多
Nitrogen(N)deposition,the source of N input into terrestrial ecosystems,is exhibiting an increasingly serious impact on the biogeochemical cycle and functional stability of ecosystems.Grasslands are an important compo...Nitrogen(N)deposition,the source of N input into terrestrial ecosystems,is exhibiting an increasingly serious impact on the biogeochemical cycle and functional stability of ecosystems.Grasslands are an important component of terrestrial ecosystems and play a key role in maintaining terrestrial ecosystem balance.Therefore,it is critical to understand the effects of nitrogen addition on grassland ecosystems.We conducted gradientN addition experiments(0,3,6,and 9 g N m^(-2)2 y^(-1))for threeyears ingrassland communities with similar site conditions.We utilized four typical herbaceous plants,including the dominant species Bothriochloa ischemum(B.ischemum)and companion species Stipa bungeana(S.bungeana),Artemisia gmelinii(A.gmelinii),and Cleistogenes squarrosa(C.squarrosa),to explore how different plant-soil-microbe systems respond to N addition.Stoichiometric homeostasis analysis demonstrated that both plants and microbes were strictly homeostatic.However,the companion species were found to be more susceptible to P dominant species.Furthermore,aggravated overlap in stoichiometric niches between plant species were observed at the N6 and N9 levels.Vector analysis indicated that the vector angle was>45°regardlessof plant species and N levels,suggesting that there was a strong Plimitation in the rhizosphere microbial community.Variation partitioning analysis revealed that the Composite roots exhibited a greater effect(explaining 34.7% of the variation)on the rhizosphere microbes than on the Gramineae,indicating that there may be more intense nutrient competition in its rhizosphere.Ingeneral,the effects of N addition on species were different a cross functional groups,with a significant positive effect on the Gramineae(B.ischemum,S.bungeana,and C.squarrosa)and a significant negative effecton the Compositae(A.gmelinii),which should be fully considered in the future ecological management and restoration.展开更多
Additive Ba（N3）2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure （about 6.0 GPa） by employing the temperatur...Additive Ba（N3）2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure （about 6.0 GPa） by employing the temperature gradient method. Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus. The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated. It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets. The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra. The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form, and the aggregated nitrogen concentration in diamond increases with temperature and duration. In addition, it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature. Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy. Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress, whereas diamond crystals heavily doped with the addition of Ba（N3）2 display the tensile stress.展开更多
Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching lo...Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching losses from both disturbed and mature forests were quite high (14.6 and 29.2 kg N ha-1 year-1, respectively), accounting for 57% and 80% of their corresponding atmospheric N inputs. N leaching losses were substantially increased following the first 1.5 years of N applications in both forests. The average increases induced by the addition of 50 and 100 kg N ha-1 year-1 were 36.5 and 24.9 kg N ha-1 year-1, respectively, in the mature forest, accounting for 73.0% and 24.9% of the annual amount of N added, and 14.2 and 16.8 kg N ha-1 year-1 in the disturbed forest, accounting for 28.4% and 16.8% of the added N. Great N leaching and a fast N leaching response to N additions in the mature forest might result from long-term N accumulation and high ambient N deposition load (greater than 30 kg N ha-1 year-1 over the past 15 years), whereas in the disturbed forest, it might result from the human disturbance and high ambient N deposition load. These results suggest that both disturbed and mature forests in the study region may be sensitive to increasing N deposition.展开更多
Deposited in plant cells and their intercellular space,phytoliths,a special form of silica,could be used to determine information on plant structure and physiology especially their size and content.With the hypothesis...Deposited in plant cells and their intercellular space,phytoliths,a special form of silica,could be used to determine information on plant structure and physiology especially their size and content.With the hypothesis that phytolith in plant would change under variable climate and environment,the dominant plant species in Songnen grassland,guinea grass(Leymus chinensis),was treated by an open-top chamber(OTC) to elevate CO2 concentration,infrared heaters,and artificial nitrogen(N) addition for three years from 2006–2008.Phytoliths were extracted by wet-ashing method and analyzed by variance analysis and so on.We found that the responses to elevated CO2 are complicated,and warming is positive while N addition is negative to the deposition of phytoliths in L.chinensis leaves.Especially,warming could reduce the negative impact of N addition on phytolith in L.chinensis.The short cell's taxonomic in graminea is significant because of no disappearance with simulated environmental changes.The phytolith originated in the long cell and plant intercellular space are more sensitive to elevated CO2 concentration,warming,and N addition,and could become some new indicators for environmental changes.In conclusion,different phytolith types have various responses to simulated warming,N addition and elevated CO2 concentration.展开更多
We examined the effects of simulated rainfall and increasing N supply of different levels on CO2 pulse emission from typical Inner Mongolian steppe soil using the static opaque chamber technique, respectively in a dry...We examined the effects of simulated rainfall and increasing N supply of different levels on CO2 pulse emission from typical Inner Mongolian steppe soil using the static opaque chamber technique, respectively in a dry June and a rainy August. The treatments included NH4NO3 additions at rates of 0, 5, 10, and 20 g N/（m2.year） with or without water. Immediately after the experimental simulated rainfall events, the CO2 effluxes in the watering plots without N addition （WCK） increased greatly and reached the maximum value at 2 hr. However, the efflux level reverted to the background level within 48 hr. The cumulative CO2 effluxes in the soil ranged from 5.60 to 6.49 g C/m2 over 48 hr after a single water application, thus showing an increase of approximately 148.64% and 48.36% in the efftuxes during both observation periods. By contrast, the addition of different N levels without water addition did not result in a significant change in soil respiration in the short term. Two-way ANOVA showed that the effects of the interaction between water and N addition were insignificant in short-term soil COz efftuxes in the soil. The cumulative soil CO2 fluxes of different treatments over 48 hr accounted for approximately 5.34% to 6.91% and 2.36% to 2.93% of annual C emission in both experimental periods. These results stress the need for improving the sampling frequency after rainfall in future studies to ensure more accurate evaluation of the grassland C emission contribution.展开更多
Recent advances in spectral sensing techniques and machine learning(ML)methods have enabled the estimation of plant physiochemical traits.Nitrogen(N)is a primary limiting factor for terrestrial forest growth,but tradi...Recent advances in spectral sensing techniques and machine learning(ML)methods have enabled the estimation of plant physiochemical traits.Nitrogen(N)is a primary limiting factor for terrestrial forest growth,but traditional methods for N determination are labor-intensive,time-consuming,and destructive.In this study,we present a rapid,non-destructive method to predict leaf N concentration(LNC)in Metasequoia glyptostroboides plantations under N and phosphorus(P)fertilization using ML techniques and unmanned aerial vehicle(UAV)-based RGB(red,green,blue)images.Nine spectral vegetation indices(VIs)were extracted from the RGB images.The spectral reflectance and VIs were used as input features to construct models for estimating LNC based on support vector machine,ran-dom forest(RF),and multiple linear regression,gradient boosting regression and classification and regression trees(CART).The results show that RF is the best fitting model for estimating LNC with a coefficient of determination(R2)of 0.73.Using this model,we evaluated the effects of N and P treatments on LNC and found a significant increase with N and a decrease with P.Height,diameter at breast height(DBH),and crown width of all M.glyptostroboides were analyzed by Pearson correlation with the predicted LNC.DBH was significantly correlated with LNC under N treat-ment.Our results highlight the potential of combining UAV RGB images with an ML algorithm as an efficient,scalable,and cost-effective method for LNC quantification.Future research can extend this approach to different tree species and different plant traits,paving the way for large-scale,time-efficient plant growth monitoring.展开更多
Background:Understanding the response of the plant community to increasing nitrogen(N)and phosphorus(P)inputs is helpful for managing and protecting grassland ecosystems in semiarid areas.However,information about dif...Background:Understanding the response of the plant community to increasing nitrogen(N)and phosphorus(P)inputs is helpful for managing and protecting grassland ecosystems in semiarid areas.However,information about different types of steppe responses to N and P availability in semiarid grasslands is limited.In 2017-2018,two field experiments were conducted with six levels of N(from 5 to 30 g N m^(−2)yr^(−1))and P(from 2.5 g to 15 g P m^(−2)yr^(−1))additions in three different temperate steppes,including meadow steppe(MS),typical steppe(TS),and desert steppe(DS),in northern China to study the effects of these addition rates on community biomass and diversity.Results:Our results showed that plant biomass and diversity in the three steppe types in Inner Mongolia responded differently to elevated N and P inputs.Increasing P promoted aboveground and belowground biomass more than increasing N in the three temperate steppes.Short-term N and P additions reduced plant diversity to some extent,with the most pronounced decreases in MS and DS.It is noteworthy that there were response thresholds for plant diversity and biomass in response to N and P inputs in different steppe types(e.g.,10 g P m^(−2)yr^(−1)).Furthermore,redundancy analysis and stepwise regression analysis revealed that changes in soil properties induced by nutrient addition and climate conditions jointly regulated changes in vegetation biomass and diversity.Conclusions:The plant biomass and diversity of three steppe types in Inner Mongolia respond divergently to elevated N and P inputs.Our results indicate that regional differences in climate and soil substrate conditions may jointly contribute to the divergent responses of plant biomass and diversity to short-term N and P addition.Our analyses provide new insights into managing and protecting grassland ecosystems.Considering that the effects of nutrient addition on plant diversity and productivity may have increasing effects over time,studies on long-term in situ nutrient addition are necessary.展开更多
N,N-deithyl-iododifluoroacetamide 1 reacted with alkenes,alkynes in aqueous aceto- nitrile solutions of sodium dithionite and sodium hydrogen carbonate at room temperature to give the corresponding adducts,thus consti...N,N-deithyl-iododifluoroacetamide 1 reacted with alkenes,alkynes in aqueous aceto- nitrile solutions of sodium dithionite and sodium hydrogen carbonate at room temperature to give the corresponding adducts,thus constituting a new method for introducing the CF_2 group into organic mol- ecules.Compound 1 reacted with conjugated olefins 2b,c to afford the iodine-free adducts 7b,c. The adducts 3d-f,from addition of 1 to alkenes 2d-f,could be converted into α,α-difluoro-γ- lactones 5d-f by treatment with silica gel.Compound 1 reacted with ethyl vinyl ether 2i to give aldehyde 8,and perfluoroalkyl or polyfluoroalkyl iodides reacted similarly.A radical mechanism was proposed for the addition reaction.Under the same condition,N,N-diethyl-bromodifluoroacetamide produced only the corresponding sulfinate Et_2NC(O)CF_2SO_2Na.展开更多
基金funded by the National Basic Research Program of China(2009CB825102)the National Basic Research Program of China(2009CB421102E)+1 种基金the International Science & Technology Cooperation Program of China(2010DFA92720)the Natural Science Foundation of China(4117049)
文摘Water and nitrogen （N） inputs are considered as the two main limiting factors affecting plant growth.Changes in these inputs are expected to alter the structure and composition of the plant community,thereby influencing biodiversity and ecosystem function.Snowfall is a form of precipitation in winter,and snow melting can recharge soil water and result in a flourish of ephemerals during springtime in the Gurbantunggut Desert,China.A bi-factor experiment was designed and deployed during the snow-covering season from 2009 to 2010.The experiment aimed to explore the effects of different snow-covering depths and N addition levels on ephemerals.Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast,N addition sharply decreased the density of ephemerals in the same snow treatment.Meanwhile,N addition exhibited a different effect on the growth of ephemeral plants：in the 50％ snow treatment,N addition limited the growth of ephemeral plants,showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth （100％ and 150％ snow treatments）,N addition benefited the growth of the dominant individual plants.Species richness was not significantly affected by snow in the same N treatment.However,N addition significantly decreased the species richness in the same snow-covering depth.The primary productivity of ephemerals in the N addition increased with the increase of snow depth.These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply.With plenty of water （100％ and 150％ snow treatments）,N addition contributed to the growth of ephemeral plants; while with less water （50％ snow treatment）,N addition restricted the growth of ephemeral plants.
基金This study was financially supported by the K.C.Wong Education Foundation,Strategic Priority Research Program of Chinese Academy of Sciences(XDA20050103)the"Light of West China"Program of the Chinese Academy of Sciences(Han W.X.).
文摘Nitrogen(N)addition has profound impacts on litter-mediated nutrient cycling.Numerous studies have reported different effects of N addition on litter decomposition,exhibiting positive,negative,or neutral effects.Previous meta-analysis of litter decomposition under N addition was mainly based on a small number of samples to allow comparisons among ecosystem types.This study presents the results of a meta-analysis incorporating data from 53 published studies(including 617 observations)across forests,grasslands,wetlands,and croplands in China,to investigate how environmental and experimental factors impact the effects of N addition on litter decomposition.Averaged across all of the studies,N addition significantly slows litter decomposition by 7.02%.Considering ecosystem types,N addition significantly accelerates litter decomposition by 3.70%and 11.22%in grasslands and wetlands,respectively,clearly inhibits litter decomposition by 14.53%in forests,and has no significant effects on litter decomposition in croplands.Regarding the accelerated litter decomposition rate in grasslands due to N addition,litter decomposition rate increases slightly with increasing rates of N addition.However,N addition slows litter decomposition in forests,but litter decomposition is at a significantly increasing rate with increasing amounts of N addition.The responses of litter decomposition to N addition are also influenced by the forms of N addition,experiential duration of N addition,humidity index,litter quality,and soil pH.In summary,N addition alters litter decomposition rate,but the direction and magnitude of the response are affected by the forms of N addition,the rate of N addition,ambient N deposition,experimental duration,and climate factors.Our study highlights the contrasting effects of N addition on litter decomposition in forests and grasslands.This finding could be used in biogeochemical models to better evaluate ecosystem carbon cycling under increasing N deposition due to the differential responses of litter decomposition to N addition rates and ecosystem types.
文摘During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition;N15: 1.5 g N/m<sup>2</sup>·a;N30: 3.0 g N/m<sup>2</sup>·a;N50: 5.0 g N/m<sup>2</sup>·a;N100: 10.0 g N/m<sup>2</sup>·a;N150: 15.0 g N/m<sup>2</sup>·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.
基金from National Natural Science Foundation of China(Grant Nos:41773075,41575137,31370494,31170421).
文摘Background:The nitrogen isotope natural abundance(δ^(15)N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ^(13)C)has been used to infer how water-using processes of plants change in terrestrial ecosystems.However,howδ^(13)C andδ^(15)N abundances in plant life and soils respond to N addition and water availability change is still unclear.Thus,δ^(13)C andδ^(15)N abundances in plant life and soils were used to investigate the effects of long-time(10 years)N addition(+50 kg N·ha^(−1)·yr^(−1)and precipitation reduction(−30%of throughfall)in forest C and N cycling traits in a temperate forest in northern China.Results:We analyzed theδ^(13)C andδ^(15)N values of dominant plant foliage,litterfall,fungal sporophores,roots,and soils in the study.The results showed thatδ^(15)N values of foliage,litterfall,and surface soil layer’s(0–10 cm)total N were significantly increased by N addition,whileδ^(15)N values of fine roots and coarse roots were considerably decreased.Nitrogen addition also significantly increased theδ^(13)C value of fine roots and total N concentration of the surface soil layer compared with the control.The C concentration,δ^(13)C,andδ^(15)N values of foliage andδ^(15)N values of fine roots were significantly increased by precipitation reduction,while N concentration of foliage and litterfall significantly decreased.The combined effects of N addition and precipitation reduction significantly increased theδ^(13)C andδ^(15)N values of foliage as well as theδ^(15)N values of fine roots andδ^(13)C values of litterfall.Furthermore,foliarδ^(15)N values were significantly correlated with foliageδ^(13)C values,surface soilδ^(15)N values,surface soil C concentration,and N concentrations.Nitrogen concentrations andδ^(13)C values of foliage were significantly correlated withδ^(15)N values and N concentrations of fine roots.Conclusions:This indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction,suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.
文摘Understanding how the growth of two key native grass species of the Northern Great Plains （Western wheatgrass and blue grama） may be affected under drought and nitrogen deficiency is essential for future management of these grasslands. The random complete block experimental design greenhouse study examined the effects of water and N addition on above-ground and below-ground harvested biomass of C3 （Western wheatgrass, WWG） and C4 （blue grama, BG） grass species for the purpose of gaining better understanding of drought responses for these two species. Compared with well-watered treatment （field capacity）, two water limited treatments （70% and 85% field capacity） decreased plant above- and below-ground biomass （WWG and BG）. For two N treatments （no N added, addition of 100 mg N kg^-1soil）, addition of N significantly improved plant above- and below-ground biomass of WWG and BG under water field capacity. Both above- and below-ground biomass of the two grass species increased linearly with increasing water supplied, but above- and below-ground biomass of WWG was always lower than BG for the same treatments （water or N addition）. The results demonstrated that BG seedlings had better adaptation than WWG to deal with the imposed drought or N deficient conditions.
基金supported by the National Natural Science Foundation of China(No.32171641,32101509,and 32271633)the Ph.D.programme grant from China Scholarship Council(202109107009).
文摘Background Changes in soil greenhouse gas(GHG)fluxes caused by nitrogen(N)addition are considered as the key factors contributing to global climate change(global warming and altered precipitation regimes),which in turn alters the feedback between N addition and soil GHG fluxes.However,the effects of N addition on soil GHG emissions under climate change are highly variable and context-dependent,so that further syntheses are required.Here,a meta-analysis of the interactive effects of N addition and climate change(warming and altered precipitation)on the fluxes of three main soil GHGs[carbon dioxide(CO_(2)),methane(CH_(4)),and nitrous oxide(N_(2)O)]was conducted by synthesizing 2103 observations retrieved from 57 peer-reviewed articles on multiple terrestrial ecosystems globally.Results The interactive effects of N addition and climate change on GHG fluxes were generally additive.The combination of N addition and warming or altered precipitation increased N_(2)O emissions significantly while it had minimal effects on CO_(2)emissions and CH_(4)uptake,and the effects on CH_(4)emissions could not be evaluated.Moreover,the magnitude of the combined effects did not differ significantly from the effects of N addition alone.Apparently,the combined effects on CO_(2)and CH_(4)varied among ecosystem types due to differences in soil moisture,which was in contrast to the soil N_(2)O emission responses.The soil GHG flux responses to combined N addition and climate change also varied among different climatic conditions and experimental methods.Conclusion Overall,our findings indicate that the effects of N addition and climate change on soil GHG fluxes were relatively independent,i.e.combined effects of N addition and climate change were equal to or not significantly different from the sum of their respective individual effects.The effects of N addition on soil GHG fluxes influence the feedbacks between climate change and soil GHG fluxes.
基金the National Basic Research Program of China (2010CB833501 973 Program)National Major Research Program of China about climate change (2010CB950603)
文摘Atmospheric nitrogen （N） deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon （C） sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition （CK： no N addition; low-N： 1 g N m-2 y-l; high-N： 2 g N m-2 y-l） on changes in mass remaining of shoot litter decomposition of three grasses （Stipa baicalensis, Carex pediformis and Leymus chinensis） over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition.
基金National Natural Science Foundation of China(30970497)Knowledge Innovation Program of the Chinese Academy of Sciences(KZCX2-YW-JC401).
文摘Aims Better understanding of microbial compositional and physiological acclimation mechanisms is critical for predicting terrestrial ecosystem responses to global change.The aim is to assess variations in soil microbial communities under future scenarios of changing precipitation and N deposition in a semiarid grassland of northern China.Methods In order to explicitly estimate microbial responses,a field experiment with water and N addition was established in April 2005 and continuously conducted for 4 years.Specifically,soil microbial community composition and microbial C utilization potential were determined by phospholipid fatty acid(PLFA)and community-level physiological profiles,respectively.Important Findings Water addition had no effects on the PLFA concentrations of grampositive(GP)and negative bacteria(GN),total bacteria and fungi.However,N addition caused significant reductions in the PLFA concentrations of GP,GN,total bacteria and fungi and thus decreased total PLFA of microbial communities.Moreover,there were interactive effects of water and N addition on GN/GPand the ratio of fungal to bacterial PLFA(F/B).In addition,synergistic effects were found between water and nitrogen in affecting microbial C utilization potentials,which implies that microbial C utilization potentials tend to be enhanced when both N and water availability are sufficient.Overall,the microbial responses to water and N addition support our hypothesis that water and N addition may be combined together to affect microbial communities in the semiarid grassland.
基金This study is financially supported by the Natural Science Key Fund for Colleges and Universities of Jiangsu Province of China(17KJA180006)the Six Talent Peaks Program of Jiangsu Province(JY-041 and TD-XYDXX-006)+1 种基金the'5151'Talent Program of Nanjing Forestry University,the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),the Doctorate Fellowship Foundation of Nanjing Forestry University,the Research Innovation Program for College Graduates of Jiangsu Province(KYLX16_0833)the Scientific and Technological Innovation Program for College Students of Nanjing Forestry University(DXSKC-201617).
文摘Aims Leaf nutrient resorption is sensitive to changes in soil nutrients.However,the effects of N deposition on nutrient resorption efficiency(NuRE)in plant macro-nutrients remain unclear.Poplar(Populus deltoids)is one of the most extensively cultivated hardwood species worldwide.We explored general patterns and dominant drivers of NuRE and stoichiometry of poplar plantations in response to N addition.Methods We conducted a 4-year N-addition experiment to explore NuRE and stoichiometric responses to N addition in two poplar(P.deltoids)plantations(8-and 12-year-old stands)in a coastal region of eastern China.We measured soil and foliar(green and senesced leaves)concentrations of nitrogen(N),phosphorus(P),potassium(K),calcium(Ca)and magnesium(Mg)for a series of N addition treatments including N_(0)(0 kg N ha^(−1)yr^(−1)),N_(1)(50 kg N ha^(−1)yr^(−1)),N_(2)(100 kg N ha^(−1)yr^(−1)),N_(3)(150 kg N ha^(−1)yr^(−1))and N_(4)(300 kg N ha^(−1)yr^(−1)).Important Findings Consistent for(both)8-and 12-year-old stands,N addition did not affect the NuRE and stoichiometry(with the exception of CaRE and CaRE:MgRE ratio).N resorption efficiency–P resorption efficiency(NRE–PRE)scaling slopes were consistently less than 1.0 under N addition.These results suggest that NRE generally decouples from PRE within each N treatment.Moreover,these results point to robust control of green leaf nutritional status on nutrient resorption processes as indicated by the positive relationships between NuRE and green leaf nutrient concentrations.Our findings provided a direct evidence that growth in 12-year-old poplar plantations was N-limited in the coastal region of eastern China.
基金This research was supported by the National Natural Science Foundation of China(41807335)the Shandong Provincial Natural Science Foundation,China(ZR2020MC040)+2 种基金the National Key Technology Research and Development Program of China(2019YFC0507602-2)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2020434)the National Postdoctoral Program for Innovative Talents(BX201700279).
文摘Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands,how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood.Therefore,we conducted an N and P addition experiment(involving control,N addition,P addition,and N+P addition)in an alpine grassland on Kunlun Mountains(Xinjiang Uygur Autonomous Region,China)in 2016 and 2017 to investigate the changes in leaf nutrient concentrations(i.e.,leaf N,Leaf P,and leaf N:P ratio)and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata,which are dominant species in this grassland.Results showed that N addition has significant effects on soil inorganic N(NO_(3)^(-)-N and NH_(4)^(+)-N)and leaf N of both species in the study periods.Compared with green leaves,leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S.rhodanthum was more sensitive to N addition,whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S.capillata.N addition did not influence N resorption efficiency of the two species.P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period.These influences on plants can be explained by increasing P availability.The present results illustrated that the two species are more sensitive to P addition than N addition,which implies that P is the major limiting factor in the studied alpine grassland ecosystem.In addition,an interactive effect of N+P addition was only discernable with respect to soil availability,but did not affect plants.Therefore,exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.
基金This work was supported by the National Natural Science Foundation of China(41401096,41171202)the National Youth Top-notch Talent Support Program in China(8200800027).
文摘Aims The productivity of forest plantations in temperate areas is often lim-ited by nitrogen(N),but may shift towards phosphorus(P)limitation with increasing atmospheric N deposition.Nutrient resorption is a nutrient conservation strategy in plants.Although data on nutrient resorption are available for overstory trees,there are few data for understory vegetation.Methods We examined leaf N and P concentrations and N and P resorption efficiencies(NRE and PRE,respectively)in eight understory species in 11-and 45-year-old Larix principis-rupprechtii stands subjected to N supplementation over a 3-year period.Important findings Leaf N concentrations and N:P ratios increased and P concentrations decreased,with N input in species within the 45-year-old stand,but not in the 11-year-old stand.NRE and PRE were not altered by N input in any of the species in either stand,but N resorption pro-ficiency decreased and P resorption proficiency increased,in the species in the 45-year-old stand.Thus,the growth of understory species may be more P-limited in the 45-versus 11-year-old stand,and nutrient resorption proficiency was more sensitive to N add-ition than nutrient resorption efficiency.These results will improve the understanding of nutrient use strategies and their responses to N addition in understory vegetation.The contrasting effects of N addition on nutrient status between stand ages cannot be ignored when modeling ecosystem nutrient cycling under global N depos-ition conditions.
基金South China Botanical Garden-Shanghai Institute of Plant Physiology&Ecology Joint Fund,Science and Technology Innovation Project of Guangdong Province Forestry(Grant No.2012KJCX019-02)the National Natural Science Foundation of China(Grant No.31370530).
文摘Aims We aimed to evaluate the changes in water-use efficiency(WuE)in native tree species in forests of subtropical China,and determine how coexisting species would be responding to increases in atmospheric carbon dioxide(CO_(2))concentrations and nitrogen(N)deposition.Methods We used model forest ecosystems in open-top chambers to study the effects of elevated CO_(2)(ca.700μmol mol−1)alone and together with N addition(NH4No3 applied at 100 kg N ha−1year−1)on WuE of four native tree species(Schima superba,Ormosia pin-nata,Castanopsis hystrix and Acmena acuminatissima)from 2006 to 2010.Important findingsour result indicated that all species increased their WuE when they were exposed to elevated CO_(2).although higher WuE was shown in faster-growing species(S.superba and O.pinnata)than that of slower-growing species(C.hystrix and Acmena acuminatissima),the increased extent of WuE induced by elevated CO_(2) was higher in the slower-growing species than that of the faster-growing species(P<0.01).the N treatment decreased WuE of S.superba,while the effects on other species were not significant.the interactions between elevated CO_(2) and N addition increased intrinsic WuE of S.superba significantly(P<0.001),however,it did not affect WuE of the other tree species significantly.We conclude that the responses of native tree species to elevated CO_(2) and N addition are different in subtropical China.the species-specific effects of elevated CO_(2) and N addition on WuE would have important implications on species composition in China’s subtropics in response to global change.
基金This work was financially supported by Shaanxi Science Fund for Distinguished Young Scholars(2021JC-50)the National Natural Science Foundation of China(41771557)Fundamental Research Funds for the Central Universities(2452021165)。
文摘Nitrogen(N)deposition,the source of N input into terrestrial ecosystems,is exhibiting an increasingly serious impact on the biogeochemical cycle and functional stability of ecosystems.Grasslands are an important component of terrestrial ecosystems and play a key role in maintaining terrestrial ecosystem balance.Therefore,it is critical to understand the effects of nitrogen addition on grassland ecosystems.We conducted gradientN addition experiments(0,3,6,and 9 g N m^(-2)2 y^(-1))for threeyears ingrassland communities with similar site conditions.We utilized four typical herbaceous plants,including the dominant species Bothriochloa ischemum(B.ischemum)and companion species Stipa bungeana(S.bungeana),Artemisia gmelinii(A.gmelinii),and Cleistogenes squarrosa(C.squarrosa),to explore how different plant-soil-microbe systems respond to N addition.Stoichiometric homeostasis analysis demonstrated that both plants and microbes were strictly homeostatic.However,the companion species were found to be more susceptible to P dominant species.Furthermore,aggravated overlap in stoichiometric niches between plant species were observed at the N6 and N9 levels.Vector analysis indicated that the vector angle was>45°regardlessof plant species and N levels,suggesting that there was a strong Plimitation in the rhizosphere microbial community.Variation partitioning analysis revealed that the Composite roots exhibited a greater effect(explaining 34.7% of the variation)on the rhizosphere microbes than on the Gramineae,indicating that there may be more intense nutrient competition in its rhizosphere.Ingeneral,the effects of N addition on species were different a cross functional groups,with a significant positive effect on the Gramineae(B.ischemum,S.bungeana,and C.squarrosa)and a significant negative effecton the Compositae(A.gmelinii),which should be fully considered in the future ecological management and restoration.
基金Project supported by the National Natural Science Foundation of China (Grant No.50572032)
文摘Additive Ba（N3）2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure （about 6.0 GPa） by employing the temperature gradient method. Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus. The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated. It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets. The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra. The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form, and the aggregated nitrogen concentration in diamond increases with temperature and duration. In addition, it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature. Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy. Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress, whereas diamond crystals heavily doped with the addition of Ba（N3）2 display the tensile stress.
基金supported by the National Natural Science Foundation of China (No.30670392)the Knowledge InnovationProgram of the Chinese Academy of Sciences (Nos.KZCX2-YW-432-2 and KSCX2-SW-133).
文摘Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching losses from both disturbed and mature forests were quite high (14.6 and 29.2 kg N ha-1 year-1, respectively), accounting for 57% and 80% of their corresponding atmospheric N inputs. N leaching losses were substantially increased following the first 1.5 years of N applications in both forests. The average increases induced by the addition of 50 and 100 kg N ha-1 year-1 were 36.5 and 24.9 kg N ha-1 year-1, respectively, in the mature forest, accounting for 73.0% and 24.9% of the annual amount of N added, and 14.2 and 16.8 kg N ha-1 year-1 in the disturbed forest, accounting for 28.4% and 16.8% of the added N. Great N leaching and a fast N leaching response to N additions in the mature forest might result from long-term N accumulation and high ambient N deposition load (greater than 30 kg N ha-1 year-1 over the past 15 years), whereas in the disturbed forest, it might result from the human disturbance and high ambient N deposition load. These results suggest that both disturbed and mature forests in the study region may be sensitive to increasing N deposition.
基金Under the auspices of National Natural Science Foundation of China(No.40971116,41471164,31170303,31270366)Ministry of Environmental Protection Foundation for Public Welfare Project(No.201109067)National Undergraduate Training Programs for Innovation and Entrepreneurship(No.201410200074)
文摘Deposited in plant cells and their intercellular space,phytoliths,a special form of silica,could be used to determine information on plant structure and physiology especially their size and content.With the hypothesis that phytolith in plant would change under variable climate and environment,the dominant plant species in Songnen grassland,guinea grass(Leymus chinensis),was treated by an open-top chamber(OTC) to elevate CO2 concentration,infrared heaters,and artificial nitrogen(N) addition for three years from 2006–2008.Phytoliths were extracted by wet-ashing method and analyzed by variance analysis and so on.We found that the responses to elevated CO2 are complicated,and warming is positive while N addition is negative to the deposition of phytoliths in L.chinensis leaves.Especially,warming could reduce the negative impact of N addition on phytolith in L.chinensis.The short cell's taxonomic in graminea is significant because of no disappearance with simulated environmental changes.The phytolith originated in the long cell and plant intercellular space are more sensitive to elevated CO2 concentration,warming,and N addition,and could become some new indicators for environmental changes.In conclusion,different phytolith types have various responses to simulated warming,N addition and elevated CO2 concentration.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KZCX2-EW-302)the National Natural Science Foundation of China(No.41330528,41373084,and 41203054)the Special Fund for Agro-scientific Research in the Public Interest(No.201203012)
文摘We examined the effects of simulated rainfall and increasing N supply of different levels on CO2 pulse emission from typical Inner Mongolian steppe soil using the static opaque chamber technique, respectively in a dry June and a rainy August. The treatments included NH4NO3 additions at rates of 0, 5, 10, and 20 g N/（m2.year） with or without water. Immediately after the experimental simulated rainfall events, the CO2 effluxes in the watering plots without N addition （WCK） increased greatly and reached the maximum value at 2 hr. However, the efflux level reverted to the background level within 48 hr. The cumulative CO2 effluxes in the soil ranged from 5.60 to 6.49 g C/m2 over 48 hr after a single water application, thus showing an increase of approximately 148.64% and 48.36% in the efftuxes during both observation periods. By contrast, the addition of different N levels without water addition did not result in a significant change in soil respiration in the short term. Two-way ANOVA showed that the effects of the interaction between water and N addition were insignificant in short-term soil COz efftuxes in the soil. The cumulative soil CO2 fluxes of different treatments over 48 hr accounted for approximately 5.34% to 6.91% and 2.36% to 2.93% of annual C emission in both experimental periods. These results stress the need for improving the sampling frequency after rainfall in future studies to ensure more accurate evaluation of the grassland C emission contribution.
基金supported by the“Pioneer”and“Leading Goose”R&D Program of Zhejiang(2022C02053)National Natural Science Foundation of China(NSFC)(32201632).
文摘Recent advances in spectral sensing techniques and machine learning(ML)methods have enabled the estimation of plant physiochemical traits.Nitrogen(N)is a primary limiting factor for terrestrial forest growth,but traditional methods for N determination are labor-intensive,time-consuming,and destructive.In this study,we present a rapid,non-destructive method to predict leaf N concentration(LNC)in Metasequoia glyptostroboides plantations under N and phosphorus(P)fertilization using ML techniques and unmanned aerial vehicle(UAV)-based RGB(red,green,blue)images.Nine spectral vegetation indices(VIs)were extracted from the RGB images.The spectral reflectance and VIs were used as input features to construct models for estimating LNC based on support vector machine,ran-dom forest(RF),and multiple linear regression,gradient boosting regression and classification and regression trees(CART).The results show that RF is the best fitting model for estimating LNC with a coefficient of determination(R2)of 0.73.Using this model,we evaluated the effects of N and P treatments on LNC and found a significant increase with N and a decrease with P.Height,diameter at breast height(DBH),and crown width of all M.glyptostroboides were analyzed by Pearson correlation with the predicted LNC.DBH was significantly correlated with LNC under N treat-ment.Our results highlight the potential of combining UAV RGB images with an ML algorithm as an efficient,scalable,and cost-effective method for LNC quantification.Future research can extend this approach to different tree species and different plant traits,paving the way for large-scale,time-efficient plant growth monitoring.
基金supported by the National Key Research and Development Program of China(2016YFA0600801).
文摘Background:Understanding the response of the plant community to increasing nitrogen(N)and phosphorus(P)inputs is helpful for managing and protecting grassland ecosystems in semiarid areas.However,information about different types of steppe responses to N and P availability in semiarid grasslands is limited.In 2017-2018,two field experiments were conducted with six levels of N(from 5 to 30 g N m^(−2)yr^(−1))and P(from 2.5 g to 15 g P m^(−2)yr^(−1))additions in three different temperate steppes,including meadow steppe(MS),typical steppe(TS),and desert steppe(DS),in northern China to study the effects of these addition rates on community biomass and diversity.Results:Our results showed that plant biomass and diversity in the three steppe types in Inner Mongolia responded differently to elevated N and P inputs.Increasing P promoted aboveground and belowground biomass more than increasing N in the three temperate steppes.Short-term N and P additions reduced plant diversity to some extent,with the most pronounced decreases in MS and DS.It is noteworthy that there were response thresholds for plant diversity and biomass in response to N and P inputs in different steppe types(e.g.,10 g P m^(−2)yr^(−1)).Furthermore,redundancy analysis and stepwise regression analysis revealed that changes in soil properties induced by nutrient addition and climate conditions jointly regulated changes in vegetation biomass and diversity.Conclusions:The plant biomass and diversity of three steppe types in Inner Mongolia respond divergently to elevated N and P inputs.Our results indicate that regional differences in climate and soil substrate conditions may jointly contribute to the divergent responses of plant biomass and diversity to short-term N and P addition.Our analyses provide new insights into managing and protecting grassland ecosystems.Considering that the effects of nutrient addition on plant diversity and productivity may have increasing effects over time,studies on long-term in situ nutrient addition are necessary.
文摘N,N-deithyl-iododifluoroacetamide 1 reacted with alkenes,alkynes in aqueous aceto- nitrile solutions of sodium dithionite and sodium hydrogen carbonate at room temperature to give the corresponding adducts,thus constituting a new method for introducing the CF_2 group into organic mol- ecules.Compound 1 reacted with conjugated olefins 2b,c to afford the iodine-free adducts 7b,c. The adducts 3d-f,from addition of 1 to alkenes 2d-f,could be converted into α,α-difluoro-γ- lactones 5d-f by treatment with silica gel.Compound 1 reacted with ethyl vinyl ether 2i to give aldehyde 8,and perfluoroalkyl or polyfluoroalkyl iodides reacted similarly.A radical mechanism was proposed for the addition reaction.Under the same condition,N,N-diethyl-bromodifluoroacetamide produced only the corresponding sulfinate Et_2NC(O)CF_2SO_2Na.
