The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering ma...The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.展开更多
To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varyi...To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varying the number of temperature cycles,the eff ects of various thinning intensities in four seasons.The rate of mass,litter organic carbon,and soil organic carbon(SOC)loss in response to temperature variations was examined in two degrees of decomposition.The unfrozen season had the highest decomposition rate of litter,followed by the frozen season.Semi-decomposed litter had a higher decomposition rate than undecomposed litter.The decomposition rate of litter was the highest when the thinning intensity was 10%,while the litter and SOC were low.Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons,while the converse was confi rmed in the frozen and thaw seasons.The best carbon sequestration impact was identifi ed in litter,and soil layers under a 20–25%thinning intensity,and the infl uence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter.Both litter and soil can store carbon:however,carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time.In summary,the best thinning intensity being 20–25%.展开更多
Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attentio...Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue.In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.展开更多
This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a ...This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a critical infrastructure and passage connecting inland China and the Qinghai–Tibet Plateau(QTP). Three technologies—global navigation satellite system(GNSS), terrestrial laser scanning(TLS), and unmanned aerial vehicle(UAV)—were used to estimate the freeze/thaw–induced 3D surface deformation of two frost mounds. Our results showed that (1) the two frost mounds exhibited mainly thaw settlement in thawing periods and frost heave in the freezing period, but frost heave dominated after repeated freeze–thaw cycles;(2) different zones of the mounds showed different deformation characteristics;(3) active-layer thickness(ALT) and elevation changes were highly correlated during thaw periods;(4) integrated 3D-measurement technologies can achieve a better understanding and assessment of hazards in the permafrost area.展开更多
We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conduc...We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.展开更多
Soil is heterogeneous and has different thermal and hydraulic properties, causing varied behavior in heat and moisture transport. Therefore, soil has an important effect on land–atmosphere interactions. In this study...Soil is heterogeneous and has different thermal and hydraulic properties, causing varied behavior in heat and moisture transport. Therefore, soil has an important effect on land–atmosphere interactions. In this study, an improved soil parameterization scheme that considers gravel and organic matter in the soil was introduced into CLM4.5(Community Land Model). By using data from the Zoige and Madoi sites on the Tibetan Plateau, the ability of the model to simultaneously simulate the duration of freeze–thaw periods, soil temperature, soil moisture, and surface energy during freeze–thaw processes, was validated. The results indicated that:(1) the new parameterization performed better in simulating the duration of the frozen, thawing, unfrozen, and freezing periods;(2) with the new scheme, the soil thermal conductivity values were decreased;(3) the new parameterization improved soil temperature simulation and effectively decreased cold biases;(4) the new parameterization scheme effectively decreased the dry biases of soil liquid water content during the freezing, completely frozen, and thawing periods, but increased the wet biases during the completely thawed period; and(5) the net radiation, latent heat flux, and soil surface heat flux of the Zoige and Madoi sites were much improved by the new organic matter and thermal conductivity parameterization.展开更多
Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but t...Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but their responses to freeze–thaw cycles(FTCs)are poorly understood.We conducted a feld freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve,China,to determine the dynamic responses of soil microbial communities to FTCs.Results:Bacteria were more sensitive than fungi to FTCs.Fungal biomass,diversity and community composition were not signifcantly afected by freeze–thaw regardless of the stage.Moderate initial freeze–thaw resulted in increased bacterial biomass,diversity,and copiotrophic taxa abundance.Subsequent FTCs reduced the bacterial biomass and diversity.Compared with the initial FTC,subsequent FTCs exerted an opposite efect on the direction of change in the composition and function of the bacterial community.Soil water content,dissolved organic carbon,ammonium nitrogen,and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs.Moreover,the functional potentials of the microbial community involved in C and N cycling were also afected by FTCs.Conclusions:Diferent stages of FTCs have diferent ecological efects on the soil environment and microbial activities.Soil FTCs changed the soil nutrients and water availability and then mainly infuenced bacterial community composition,diversity,and functional potentials,which may disturb C and N states in this temperate forest soil.This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.展开更多
The near-surface soil freeze–thaw(FT)transition is an important factor affecting land-atmosphere exchanges,hydrology and carbon cycles.Thus,effectively monitoring the temporal–spatial changes of soil FT processes is...The near-surface soil freeze–thaw(FT)transition is an important factor affecting land-atmosphere exchanges,hydrology and carbon cycles.Thus,effectively monitoring the temporal–spatial changes of soil FT processes is crucial to climate change and environment research.Several approaches have been developed to detect the soil FT state from satellite observations.The discriminant function algorithm(DFA)uses temperature and emissivity information from Advanced Microwave Scanning Radiometer Enhanced(AMSR-E)passive microwave satellite observations.Although it is well validated,it was shown to be insufficiently robust for all land conditions.In this study,we use in-situ observed soil temperature and AMSR-E brightness temperature to parameterize the DFA for soil FT state detection.We use the in-situ soil temperature records at 5 cm selected from available dense networks in the Northern Hemisphere as a reference.Considering the distinction between ascending and descending orbits,two different sets of parameters were acquired for each frequency pair.The validation results indicate that the overall discriminant accuracy of the new function can reach 90%.We further compared the Advanced Microwave Scanning Radiometer 2 discriminant results using the new function to the Soil Moisture Active Passive freeze/thaw product,and a reasonable consistency between them was found.展开更多
Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one ...Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one of the important factors affecting the durability of concrete constructions. To realize fully the interaction between various environmental factors, this paper researched concrete durability in the salt environment under combined actions(immersing, freeze–thaw cycles, and wet–dry cycles). According to the laboratory test data, the concrete-durability degradation law under coupling-effect factors was investigated. The results show that concrete's compressive strength decreases with the increase of salt concentration and immersion time. No matter what the environmental conditions were, the compressive strength-loss ratio increased with the test time. The compressive strength-test results indicate that sodium sulfate has the strongest corrosive effect on concrete durability, followed by calcium chloride, with sodium chloride having the weakest corrosion. Compared with the other two environmental factors, the wet–dry cycle is the key factor affecting concrete durability. Therefore, in engineering practice, the influence of environment conditions on the strength and durability of concrete should be taken into full consideration, especially in the wet–dry environment with salt conditions.展开更多
portion of alpine meadows has been and will continue to be cultivated due to the concurrent increasing demands for animal-and crop-oriented foods and global warming.However, it remains unclear how these long-term chan...portion of alpine meadows has been and will continue to be cultivated due to the concurrent increasing demands for animal-and crop-oriented foods and global warming.However, it remains unclear how these long-term changes in land use will affect nitric oxide(NO) emission. At a field site with a calcareous soil on the Qinghai-Tibetan Plateau,the authors measured the year-round NO fluxes and related variables in a typically wintergrazed natural alpine meadow(NAM) and its adjacent forage oat field(FOF). The results showed that long-term plow tillage, fertilization and growing forage oats significantly yielded ca. 2.7 times more(p < 0.01) NO emissions from the FOF than the NAM(conservatively 208 vs. 56 g N/(ha·year) on average). The spring freeze–thaw period and non-growing season accounted for 17%-35% of the annual emissions, respectively. The Q10 of surface soil temperature(Ts) was 8.9 in the NAM(vs. 3.8 in the FOF), indicating increases of 24%–93% in NO emissions per 1–3 °C increase. However, the warming-induced increases could be smaller than those due to land use change and management practices. The Tsand concentrations of ammonium, nitrate and water-extractable organic carbon jointly explained 69% of the variance in daily NO fluxes from both fields during the annual period(p < 0.001). This result indicates that temporally and/or spatially distributed NO fluxes from landscapes with calcareous soils across native alpine meadows and/or fields cultivated with forage oats can be predicted by simultaneous observations of these four soil variables.展开更多
基金supported by Shandong Provincial Natural Science Foundation (grant number: ZR2023MD036)Key Research and Development Project in Shandong Province (grant number: 2019GGX101064)project for excellent youth foundation of the innovation teacher team, Shandong (grant number: 2022KJ310)。
文摘The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.
基金funded by the National Key R&D Program of China(2017YFC0504103)Project for Applied Technology Research and Development in Heilongjiang Province(GA19C006).
文摘To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning,we assessed the potential impact of thinning intensity on carbon cycle dynamics.By varying the number of temperature cycles,the eff ects of various thinning intensities in four seasons.The rate of mass,litter organic carbon,and soil organic carbon(SOC)loss in response to temperature variations was examined in two degrees of decomposition.The unfrozen season had the highest decomposition rate of litter,followed by the frozen season.Semi-decomposed litter had a higher decomposition rate than undecomposed litter.The decomposition rate of litter was the highest when the thinning intensity was 10%,while the litter and SOC were low.Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons,while the converse was confi rmed in the frozen and thaw seasons.The best carbon sequestration impact was identifi ed in litter,and soil layers under a 20–25%thinning intensity,and the infl uence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter.Both litter and soil can store carbon:however,carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time.In summary,the best thinning intensity being 20–25%.
基金supported by "the Fundamental Research Funds for the Central Universities" (Grant No. 2015B25014)"the Practical Innovation Program for Postgraduate Students of Jiangsu Province, China" (Grant No. SJZZ15_0058)+1 种基金funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) (Grant No. 3014–SYS1401)the organizing committee of "XI International Symposium on Permafrost Engineering (Magadan, Russia, Sept. 5-8, 2017)" for giving the opportunity to exchange this study
文摘Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue.In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.
基金supported by the National Natural Science Foundation of China (41301508, 41630636)
文摘This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a critical infrastructure and passage connecting inland China and the Qinghai–Tibet Plateau(QTP). Three technologies—global navigation satellite system(GNSS), terrestrial laser scanning(TLS), and unmanned aerial vehicle(UAV)—were used to estimate the freeze/thaw–induced 3D surface deformation of two frost mounds. Our results showed that (1) the two frost mounds exhibited mainly thaw settlement in thawing periods and frost heave in the freezing period, but frost heave dominated after repeated freeze–thaw cycles;(2) different zones of the mounds showed different deformation characteristics;(3) active-layer thickness(ALT) and elevation changes were highly correlated during thaw periods;(4) integrated 3D-measurement technologies can achieve a better understanding and assessment of hazards in the permafrost area.
基金supported by grants from the National Key Research and Development Program of China(Grant No.2016YFD0600401)the Liaoning Provincial Key Research Project for Agriculture(Grant No.2015103002)
文摘We analyzed the relationships linking overwintering death and frost cracking to temperature and sunlight as well as the effects of low temperatures and freeze–thaw cycles on bud-burst rates,relative electrical conductivity,and phloem and cambial ultrastructures of poplar.Overwintering death rates of poplar were not correlated with negative accumulated temperature or winter minimum temperature.Freeze–thaw cycles caused more bud damage than constant exposure to low temperatures.Resistance to freeze–thaw cycles differed among clones,and the budburst rate decreased with increasing exposure to freeze–thaw cycles.Cold-resistant clones had the lowest relative electrical conductivity.Chloroplasts exhibited the fastest and the most obvious reaction to freeze–thaw damage,whereas a single freeze–thaw cycle caused little damage to cambium ultrastructure.Several such cycles resulted in damage to plasma membranes,severe damage to organelles,dehydration of cells and cell death.We conclude that overwintering death of poplar is mainly attributed to the accumulation of effective freeze–thaw damage beyond the limits of freeze–thaw resistance.
基金Supported by the National Natural Science Foundation of China(91537104,41375077,91537106,and 91537214)
文摘Soil is heterogeneous and has different thermal and hydraulic properties, causing varied behavior in heat and moisture transport. Therefore, soil has an important effect on land–atmosphere interactions. In this study, an improved soil parameterization scheme that considers gravel and organic matter in the soil was introduced into CLM4.5(Community Land Model). By using data from the Zoige and Madoi sites on the Tibetan Plateau, the ability of the model to simultaneously simulate the duration of freeze–thaw periods, soil temperature, soil moisture, and surface energy during freeze–thaw processes, was validated. The results indicated that:(1) the new parameterization performed better in simulating the duration of the frozen, thawing, unfrozen, and freezing periods;(2) with the new scheme, the soil thermal conductivity values were decreased;(3) the new parameterization improved soil temperature simulation and effectively decreased cold biases;(4) the new parameterization scheme effectively decreased the dry biases of soil liquid water content during the freezing, completely frozen, and thawing periods, but increased the wet biases during the completely thawed period; and(5) the net radiation, latent heat flux, and soil surface heat flux of the Zoige and Madoi sites were much improved by the new organic matter and thermal conductivity parameterization.
基金The National Natural Science Foundation of China(31770531,32001174)the Key Research Program of Frontier Sciences,CAS(QYZDB-SSW-DQC006)+1 种基金the Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains,Ministry of Education(GPES201902)the Youth Innovation Promotion Association CAS to Chao Wang(2018231).
文摘Background:Freeze–thaw events are common in boreal and temperate forest ecosystems and are increasingly infuenced by climate warming.Soil microorganisms play an important role in maintaining ecosystem stability,but their responses to freeze–thaw cycles(FTCs)are poorly understood.We conducted a feld freeze–thaw experiment in a natural Korean pine and broadleaf mixed forest in the Changbai Mountain Nature Reserve,China,to determine the dynamic responses of soil microbial communities to FTCs.Results:Bacteria were more sensitive than fungi to FTCs.Fungal biomass,diversity and community composition were not signifcantly afected by freeze–thaw regardless of the stage.Moderate initial freeze–thaw resulted in increased bacterial biomass,diversity,and copiotrophic taxa abundance.Subsequent FTCs reduced the bacterial biomass and diversity.Compared with the initial FTC,subsequent FTCs exerted an opposite efect on the direction of change in the composition and function of the bacterial community.Soil water content,dissolved organic carbon,ammonium nitrogen,and total dissolved phosphorus were important factors determining bacterial community diversity and composition during FTCs.Moreover,the functional potentials of the microbial community involved in C and N cycling were also afected by FTCs.Conclusions:Diferent stages of FTCs have diferent ecological efects on the soil environment and microbial activities.Soil FTCs changed the soil nutrients and water availability and then mainly infuenced bacterial community composition,diversity,and functional potentials,which may disturb C and N states in this temperate forest soil.This study also improves our understanding of microbial communities regulating their ecological functions in response to climate change.
基金the National Key Basic Research Program of China(2015CB953701)National Natural Science Foundation of China(41671355)+2 种基金Chinese Academy of Sciences Key Research Program of Frontier Sciences(QYZDY-SSW-DQC011)Strategic Pionner Program on Space Science(XDA15052300)‘Light of West China’Program and Youth Innovation Promotion Association(No.2016061).
文摘The near-surface soil freeze–thaw(FT)transition is an important factor affecting land-atmosphere exchanges,hydrology and carbon cycles.Thus,effectively monitoring the temporal–spatial changes of soil FT processes is crucial to climate change and environment research.Several approaches have been developed to detect the soil FT state from satellite observations.The discriminant function algorithm(DFA)uses temperature and emissivity information from Advanced Microwave Scanning Radiometer Enhanced(AMSR-E)passive microwave satellite observations.Although it is well validated,it was shown to be insufficiently robust for all land conditions.In this study,we use in-situ observed soil temperature and AMSR-E brightness temperature to parameterize the DFA for soil FT state detection.We use the in-situ soil temperature records at 5 cm selected from available dense networks in the Northern Hemisphere as a reference.Considering the distinction between ascending and descending orbits,two different sets of parameters were acquired for each frequency pair.The validation results indicate that the overall discriminant accuracy of the new function can reach 90%.We further compared the Advanced Microwave Scanning Radiometer 2 discriminant results using the new function to the Soil Moisture Active Passive freeze/thaw product,and a reasonable consistency between them was found.
基金supported by the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (QYZDYSSW-DQC015)the funding of the State Key Laboratory of Frozen Soil Engineering (No. SKLFSE-ZT-17)
文摘Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one of the important factors affecting the durability of concrete constructions. To realize fully the interaction between various environmental factors, this paper researched concrete durability in the salt environment under combined actions(immersing, freeze–thaw cycles, and wet–dry cycles). According to the laboratory test data, the concrete-durability degradation law under coupling-effect factors was investigated. The results show that concrete's compressive strength decreases with the increase of salt concentration and immersion time. No matter what the environmental conditions were, the compressive strength-loss ratio increased with the test time. The compressive strength-test results indicate that sodium sulfate has the strongest corrosive effect on concrete durability, followed by calcium chloride, with sodium chloride having the weakest corrosion. Compared with the other two environmental factors, the wet–dry cycle is the key factor affecting concrete durability. Therefore, in engineering practice, the influence of environment conditions on the strength and durability of concrete should be taken into full consideration, especially in the wet–dry environment with salt conditions.
基金supported by the Ministry of Science and Technology of China(2016YFA0602303)the National Natural Science Foundation of China(41375152,41603075,and 41775141)
文摘portion of alpine meadows has been and will continue to be cultivated due to the concurrent increasing demands for animal-and crop-oriented foods and global warming.However, it remains unclear how these long-term changes in land use will affect nitric oxide(NO) emission. At a field site with a calcareous soil on the Qinghai-Tibetan Plateau,the authors measured the year-round NO fluxes and related variables in a typically wintergrazed natural alpine meadow(NAM) and its adjacent forage oat field(FOF). The results showed that long-term plow tillage, fertilization and growing forage oats significantly yielded ca. 2.7 times more(p < 0.01) NO emissions from the FOF than the NAM(conservatively 208 vs. 56 g N/(ha·year) on average). The spring freeze–thaw period and non-growing season accounted for 17%-35% of the annual emissions, respectively. The Q10 of surface soil temperature(Ts) was 8.9 in the NAM(vs. 3.8 in the FOF), indicating increases of 24%–93% in NO emissions per 1–3 °C increase. However, the warming-induced increases could be smaller than those due to land use change and management practices. The Tsand concentrations of ammonium, nitrate and water-extractable organic carbon jointly explained 69% of the variance in daily NO fluxes from both fields during the annual period(p < 0.001). This result indicates that temporally and/or spatially distributed NO fluxes from landscapes with calcareous soils across native alpine meadows and/or fields cultivated with forage oats can be predicted by simultaneous observations of these four soil variables.
