A cruise was conducted from late August to early September 2004 with the intention of obtaining an interdisciplinary understanding of the Yangtze River Estuary including the biological, chemical and physical subjects....A cruise was conducted from late August to early September 2004 with the intention of obtaining an interdisciplinary understanding of the Yangtze River Estuary including the biological, chemical and physical subjects. Water sample analysis indicated that total phytoplankton species richness was 137. Of them 81 were found in Bacillariophyta and 48 in Pyrrophyta, accounting for 59.1% and 35.0% respectively. The average cell abundance of surface water samples was 8.8 ×104 cells L^-1, with the maximum, 102.9×104 cells L^-1, encountered in the area （31.75°N, 122.33°E） and the minimum, 0.2×10^4 cells L^-1, in （30.75°N, 122.17°E）. The dominant species at most stations were Skeletonema costatum and Proboscia alata f. gracillima with the dominance of 0.35 and 0.27. Vertical distribution analysis indicated that obvious stratification of cell abundance and dominant species was found in the representative stations of 5, 18 and 33. Shannon-Wiener index and evenness of phytoplankton assemblage presented negative correlation with the cell abundance, with the optimum appearing in （30.75°N, 122.67°E）. According to the PCA analysis of the environmental variables, elevated nutrients of nitrate, silicate and phosphate through river discharge were mainly responsible for the phytoplankton bloom in this area.展开更多
Purplish soils having high fertility with mineral nutrients inherited from the parent rock are widely distributed in the hills along the Yangtze River,especially in the Sichuan Basin.Pot and field weathering experimen...Purplish soils having high fertility with mineral nutrients inherited from the parent rock are widely distributed in the hills along the Yangtze River,especially in the Sichuan Basin.Pot and field weathering experiments were conducted to mimic rock weathering and nutrient release processes in order to better understand soil fertility and nutrient compensation. Three types of purplish rock formations formed in the Jurassic period,Shaximiao(J_2s),Suining(J_3s),and Penglaizhen (J_3p),as well as one type formed in the Cretaceous period,the Chengqiangyan group(K_1c),were used in this study. Results showed that the soil formation rate was in the range from 11.2 to 19.6 mm every year,and rock weathering was in the order of J_3s>J_3p>J_2s>K_1c.Because more rock surface was exposed to sunlight and rainfall in field conditions,pot weathering was slower than field weathering.Nutrient release rates increased with rock weathering and was in the order similar to that of rock weathering:J_3p>J_3s>J_2s>K_1c.Potassium release was the most important in all rocks;after 2 years of weathering,19.4% to 46.9% of K was released from the initial parent rocks,which suggested that K release from weathering could meet most of the crop K requirement in purplish soils.Thus,rapid release of nutrients from weathering of purplish rocks was key to nutrient replenishment and fertility of purplish soils.展开更多
The leaching and redistribution of nutrients in the surface layer of 4 types of red soils in SoutheastChina were studied with a lysimeter experiment under field conditions. Results showed that the leachingconcentrated...The leaching and redistribution of nutrients in the surface layer of 4 types of red soils in SoutheastChina were studied with a lysimeter experiment under field conditions. Results showed that the leachingconcentrated in the rainy season (from April to June). Generaily, the leaching of soil nutrients from thesurface layer of red soils was in the order of Ca > Mg > K > NO3-N. In fertilization treatment, the totalamount of soil nutrients leached out of the surface layer in a red soil derived from granite was the highest inall soils. The uptake by grass decreased the leaching of fertilizer ions in surface layer, particularly for NO3-N.Soil total N and exchangeable K, Ca and Mg in the surface layer decreased with leaching and grass uptakeduring the 2 years without new fertilization of urea, Ca(H2PO4)2, KCl, CaCO3 and MgCO3. Ca movedfrom the application layer (0~5 cm) of fertilizer and accumulated in the 10~30 cm depth in the soils studiedexcept that derived from Quaternary red clay. The deficiency of soil exchangeable K will become a seriousdegradation process facing the Southeast China.展开更多
Nutrition is an important factor for the growth and development of plants. Among the main nutritional elements, there are nitrogen （N） and calcium （Ca）. The N comes from two forms of inorganic ions, ammonium （NH...Nutrition is an important factor for the growth and development of plants. Among the main nutritional elements, there are nitrogen （N） and calcium （Ca）. The N comes from two forms of inorganic ions, ammonium （NH4＋） and nitrate （NO3） whose functions in the plant are the increase in leaf area and improving the succulence of many crops, among other essential physiological processes. Both the deficit and excess NO3- have a negative impact on plants increasing susceptibility to insect pests and pathogens, while Ca as divalent ion absorbed Ca2＋ plays an important role in control of physiological disorders and the resistance of plants to diseases to increase the mechanical strength. The N and Ca have a close relationship in the nutritional role of the plant, because the Ca absorption acting nitrates, so that a proper balance affects plants better growth and higher strength.展开更多
Both nitrate((NO_3)^-) and soluble reactive phosphate((PO_4)^(3-)) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s.Within the same period in ...Both nitrate((NO_3)^-) and soluble reactive phosphate((PO_4)^(3-)) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s.Within the same period in the sea area,with surface salinity>30,(NO_3)^-concentration has shown an obvious increase,(PO_4)^(3-) has not changed greatly and dissolved reactive silica((SiO_3)^(2-)) has deceased dramatically.An examination of the elemental ratio of(NO_3)^-to(PO_4)^(3-) at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients increased simultaneously.In comparison,the elemental ratio of dissolved inorganic nitrogen(DIN) to(PO_4)^(3-) in surface seawater,with salinity>22,has shown a clearly increasing trend.Furthermore,an overall historical change of the(SiO_3)^(2-):(PO_4)^(3-) ratio has undergone a reverse trend in this area.Based on the changes of(SiO_3)^(2-):(PO_4)^(3-) and DIN:(PO_4)^(3-) ratios,we can conclude that an overall historical change of(SiO_3)^(2-):DIN ratio has decreased in this area from the 1950-1960s to 2000s.The argument that phytoplankton productivity in the Changjiang estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results.A comparative study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made.The results indicated that the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985-1986 to 69.8% during 2004-2005.Furthermore,the average yearly percentage of diatom abundance in the Changjiang estuary decreased from 99.5% during to 75.5% over the same time period,while the abundance of dinoflagellates has increased dramatically,from 0.7% to 25.4%.展开更多
The influence of soil chemical properties and soil nutrition on cotton yields was studied by means of establishing mathematical models.The nultivarate quadratic regression equations developed by a stepwise regression ...The influence of soil chemical properties and soil nutrition on cotton yields was studied by means of establishing mathematical models.The nultivarate quadratic regression equations developed by a stepwise regression method not only presented the single effect of soil factors but also displayed the interaction(synergistic or antagonistic) of soil nutrients.The effect of individual factor and the way of nutrient interaction were further analysed by the path analysis method.The results showed that among major factors affecting cotton yields,there existed the interactions between macronutrients(available P× available K),and between macronutrients and microelements(N×Zn,P×Mo,P×Cu,P×Zn,K×Mo)besides the single effect of soil pH,total P ,available Cu and available Zn.展开更多
OBJECTIVE To explore the potential neurotrophic effect of bone marrow stromal cells （BMSCs） on cell proliferation and committed neuronal differentiation of ventral mesencephalic precursors （VMPs） in vitro. METHODS...OBJECTIVE To explore the potential neurotrophic effect of bone marrow stromal cells （BMSCs） on cell proliferation and committed neuronal differentiation of ventral mesencephalic precursors （VMPs） in vitro. METHODS Ventral mesencephalic precursors from Ell inbred rat embryos and BMSCs from adult rats were cultured both separately and in co-culture. After a 7-day incubation in vitro, three conditioned culture media were obtained, termed VMP or common medium, BMSC medium, and BMSC±VMP medium. Ventral mesen- cephalic precursors cells were cultured in each of these media and the effects on proliferation and VMP differentiation were assessed. The relative yield of TH± cells was calculated and compared by immunocytochemical staining. RESULTS After a 7-day culture and induction of VMPs, the total cell counts were increased by （44.13±4.75）-fold （common）, （60.63±5.25）-fold （BMSC）, and （64.00±7.63）-fold （BMSC±VMP）. The proportions of TH＋ cells were （18.76±5.20）%, （23.49±4.10）%, and （28.08± 5.42）%, respectively, with statistically significant differences among the treatment groups. CONCLUSION BMSCs release factors that promote the proliferation of VMPs and facilitate the committed differentiation of VMPs into dopaminergic neurons.展开更多
Understanding the pattern ofphytoplankton and their dependence on water quality variables, can help the management of eutrophic lakes. The aim of this study was to determine water quality and environmental factors ass...Understanding the pattern ofphytoplankton and their dependence on water quality variables, can help the management of eutrophic lakes. The aim of this study was to determine water quality and environmental factors associated with cyanobacteria dominance and microcystin production in Qingshan Lake, a subtropical lake located in the headwater of the Taihu watershed, China. Water samples collected monthly from 10 study sites in Qingshan Lake were analyzed for the species distributions of freshwater algae and physico-chemical parameters including total nitrogen （TN）, ammonia （NH4＋-N）, nitrate （NO3--N）, total phosphorus （TP）, and chlorophyll a （Chl-a） from June, 2008 to May, 2009. Qingshan Lake was found to be eutrophic, based on the calculated trophic state index （TSI）. The average TN of 4.33 mg/L during the study period exceeded the Surface Water Quality Standards of China. TP was significantly correlated with relative abundance of cyanobacteria and Microeystis biovolume, indi- cating its important role in regulating cyanobacteria. Microcystis, Anabaena, and Oscillatoria were dominant cyanobacteria in Qingshan Lake from June to November, 2008. Cyanobacteria dominance was regulated by water temperature and TE Principal component analysis further indicated that microcystin production was most affected by water temperature, TP, and cyanobacteria biomass. Results suggest that the control of TP in summer can mitigate cyanobacteria dominance and microcystin production in Qingshan Lake, and close monitoring should be undertaken in summer.展开更多
We consider a model of the exploitative competition of two micro-organisms for two complementary nutrients in a chemostat and take into account the interspecific interac- tion. The growth functions occurring in the mo...We consider a model of the exploitative competition of two micro-organisms for two complementary nutrients in a chemostat and take into account the interspecific interac- tion. The growth functions occurring in the model are of general type and the interaction functions are monotonic and positive. By the mean of the Thieme-Zhao theorem, we establish conditions for uniform persistence of the model.展开更多
Objective： The aim of this study was to test the protective effect of mesenchymal stem cells （MSCs） on cardiomyocytes in vitro and to investigate the anti-apoptotic signaling pathway. Methods： MSCs from Sprague-Da...Objective： The aim of this study was to test the protective effect of mesenchymal stem cells （MSCs） on cardiomyocytes in vitro and to investigate the anti-apoptotic signaling pathway. Methods： MSCs from Sprague-Dawley （SD） rats were separated and cultured. MSC medium was collected from MSCs （DMEM） under hypoxia. Cultured cardiomyocytes from neonatal cultured in serum-free Dulbecco＇s modified eagle medium SD rats were exposed to hypoxia/reoxygenation （H/R） and treated with MSC medium. The apoptotic cardiomyocytes were stained with Annexin-V-fluorescein isothiocyanate （FITC）, Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling （TUNEL）. The mitochondrial transmembrane potential of cardiomyocytes was assessed using a fluorescence microscope. The expression of Bcl-2, Bax, cyto- chrome C, apoptosis-induced factor （AIF）, and caspase-3 was tested by Western blot analysis. Results： Our data demonstrated that MSC medium reduced H/R-induced cardiomyocyte apoptosis, increased the Bcl-2/Bax ratio, and reduced the release of cyto- chrome C and AIF from mitochondria into the cytosol. Conclusion： MSCs protected the cardiomyocytes from H/R-induced apoptosis through a mitochondrial pathway in a paracrine manner.展开更多
Aims Although increases in precipitation variability in arid ecosystems are projected due to climate change,the response of desert shrub communities to precipitation change has not been fully elucidated.Such knowledge...Aims Although increases in precipitation variability in arid ecosystems are projected due to climate change,the response of desert shrub communities to precipitation change has not been fully elucidated.Such knowledge is important since drought-adapted plants exhibit varied mechanisms of survival that may contribute to species coexistence.Methods We tested the responses of eight drought-adapted plants,a mix of graminoids,shrubs and forbs to three summer precipitation scenarios(1.3,2.6 and 3.9 cm per month)in a common garden experiment in the Great Basin(Owens Valley,California).Changes in mineral nutrient uptake(carbon,nitrogen,phosphorus,potassium,calcium,magnesium,manganese,copper,boron,zinc,iron and sodium)and gas exchange parameters(photosynthetic rate and stomatal conductance)were investigated in the studied species.Important Findings Two graminoids(Sporobolus airoides and Leymus triticoides)and one salt tolerant shrub species(Atriplex confertifolia)responded to increased water availability with increases in photosynthetic rate and/or stomatal conductance.There was a significant correlation between water availability and uptake of nutrients for five out of eight species.Artemisia tridentata,with higher rates of photosynthesis,contained greater amounts of potassium,copper and boron,while Juncus arcticus,with higher rates of photosynthesis,contained greater amounts of magnesium and iron,and less sodium.Juncus arcticus and three salt-adapted species(A.confertifolia,Distichlis spicata and S.airoides)exhibited correlations with stomatal conductance and concentrations of nutrients.Results indicate that differential physiological response mechanisms to increased moisture and associated nutrient uptake strategies in drought-adapted species may mediate coexistence under increased summer precipitation.展开更多
Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,tra...Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.展开更多
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.50339040,40306025)the Chinese Academy of Sciences(No.KZCX3-SW-232).The authors are also very much indebted to the crews of the cruise.
文摘A cruise was conducted from late August to early September 2004 with the intention of obtaining an interdisciplinary understanding of the Yangtze River Estuary including the biological, chemical and physical subjects. Water sample analysis indicated that total phytoplankton species richness was 137. Of them 81 were found in Bacillariophyta and 48 in Pyrrophyta, accounting for 59.1% and 35.0% respectively. The average cell abundance of surface water samples was 8.8 ×104 cells L^-1, with the maximum, 102.9×104 cells L^-1, encountered in the area （31.75°N, 122.33°E） and the minimum, 0.2×10^4 cells L^-1, in （30.75°N, 122.17°E）. The dominant species at most stations were Skeletonema costatum and Proboscia alata f. gracillima with the dominance of 0.35 and 0.27. Vertical distribution analysis indicated that obvious stratification of cell abundance and dominant species was found in the representative stations of 5, 18 and 33. Shannon-Wiener index and evenness of phytoplankton assemblage presented negative correlation with the cell abundance, with the optimum appearing in （30.75°N, 122.67°E）. According to the PCA analysis of the environmental variables, elevated nutrients of nitrate, silicate and phosphate through river discharge were mainly responsible for the phytoplankton bloom in this area.
基金the National Basic Research Program of China(No.2003CB415202)the National Natural Science Foundation of China(Nos.40571093 and 49601009)
文摘Purplish soils having high fertility with mineral nutrients inherited from the parent rock are widely distributed in the hills along the Yangtze River,especially in the Sichuan Basin.Pot and field weathering experiments were conducted to mimic rock weathering and nutrient release processes in order to better understand soil fertility and nutrient compensation. Three types of purplish rock formations formed in the Jurassic period,Shaximiao(J_2s),Suining(J_3s),and Penglaizhen (J_3p),as well as one type formed in the Cretaceous period,the Chengqiangyan group(K_1c),were used in this study. Results showed that the soil formation rate was in the range from 11.2 to 19.6 mm every year,and rock weathering was in the order of J_3s>J_3p>J_2s>K_1c.Because more rock surface was exposed to sunlight and rainfall in field conditions,pot weathering was slower than field weathering.Nutrient release rates increased with rock weathering and was in the order similar to that of rock weathering:J_3p>J_3s>J_2s>K_1c.Potassium release was the most important in all rocks;after 2 years of weathering,19.4% to 46.9% of K was released from the initial parent rocks,which suggested that K release from weathering could meet most of the crop K requirement in purplish soils.Thus,rapid release of nutrients from weathering of purplish rocks was key to nutrient replenishment and fertility of purplish soils.
文摘The leaching and redistribution of nutrients in the surface layer of 4 types of red soils in SoutheastChina were studied with a lysimeter experiment under field conditions. Results showed that the leachingconcentrated in the rainy season (from April to June). Generaily, the leaching of soil nutrients from thesurface layer of red soils was in the order of Ca > Mg > K > NO3-N. In fertilization treatment, the totalamount of soil nutrients leached out of the surface layer in a red soil derived from granite was the highest inall soils. The uptake by grass decreased the leaching of fertilizer ions in surface layer, particularly for NO3-N.Soil total N and exchangeable K, Ca and Mg in the surface layer decreased with leaching and grass uptakeduring the 2 years without new fertilization of urea, Ca(H2PO4)2, KCl, CaCO3 and MgCO3. Ca movedfrom the application layer (0~5 cm) of fertilizer and accumulated in the 10~30 cm depth in the soils studiedexcept that derived from Quaternary red clay. The deficiency of soil exchangeable K will become a seriousdegradation process facing the Southeast China.
文摘Nutrition is an important factor for the growth and development of plants. Among the main nutritional elements, there are nitrogen （N） and calcium （Ca）. The N comes from two forms of inorganic ions, ammonium （NH4＋） and nitrate （NO3） whose functions in the plant are the increase in leaf area and improving the succulence of many crops, among other essential physiological processes. Both the deficit and excess NO3- have a negative impact on plants increasing susceptibility to insect pests and pathogens, while Ca as divalent ion absorbed Ca2＋ plays an important role in control of physiological disorders and the resistance of plants to diseases to increase the mechanical strength. The N and Ca have a close relationship in the nutritional role of the plant, because the Ca absorption acting nitrates, so that a proper balance affects plants better growth and higher strength.
基金Supported by the National Natural Science Foundation of China for Creative Research Groups(No.40821004)the High Technology Research and Development Program of China(863 Program)(No.2008AA09Z107)the National Basic Research Program of China(973 Program)(No.2010CB428706)
文摘Both nitrate((NO_3)^-) and soluble reactive phosphate((PO_4)^(3-)) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s.Within the same period in the sea area,with surface salinity>30,(NO_3)^-concentration has shown an obvious increase,(PO_4)^(3-) has not changed greatly and dissolved reactive silica((SiO_3)^(2-)) has deceased dramatically.An examination of the elemental ratio of(NO_3)^-to(PO_4)^(3-) at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients increased simultaneously.In comparison,the elemental ratio of dissolved inorganic nitrogen(DIN) to(PO_4)^(3-) in surface seawater,with salinity>22,has shown a clearly increasing trend.Furthermore,an overall historical change of the(SiO_3)^(2-):(PO_4)^(3-) ratio has undergone a reverse trend in this area.Based on the changes of(SiO_3)^(2-):(PO_4)^(3-) and DIN:(PO_4)^(3-) ratios,we can conclude that an overall historical change of(SiO_3)^(2-):DIN ratio has decreased in this area from the 1950-1960s to 2000s.The argument that phytoplankton productivity in the Changjiang estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results.A comparative study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made.The results indicated that the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985-1986 to 69.8% during 2004-2005.Furthermore,the average yearly percentage of diatom abundance in the Changjiang estuary decreased from 99.5% during to 75.5% over the same time period,while the abundance of dinoflagellates has increased dramatically,from 0.7% to 25.4%.
文摘The influence of soil chemical properties and soil nutrition on cotton yields was studied by means of establishing mathematical models.The nultivarate quadratic regression equations developed by a stepwise regression method not only presented the single effect of soil factors but also displayed the interaction(synergistic or antagonistic) of soil nutrients.The effect of individual factor and the way of nutrient interaction were further analysed by the path analysis method.The results showed that among major factors affecting cotton yields,there existed the interactions between macronutrients(available P× available K),and between macronutrients and microelements(N×Zn,P×Mo,P×Cu,P×Zn,K×Mo)besides the single effect of soil pH,total P ,available Cu and available Zn.
基金This work was supported by grants from Natural Science Foundation of Jiangsu Province （No.BK2004043）
文摘OBJECTIVE To explore the potential neurotrophic effect of bone marrow stromal cells （BMSCs） on cell proliferation and committed neuronal differentiation of ventral mesencephalic precursors （VMPs） in vitro. METHODS Ventral mesencephalic precursors from Ell inbred rat embryos and BMSCs from adult rats were cultured both separately and in co-culture. After a 7-day incubation in vitro, three conditioned culture media were obtained, termed VMP or common medium, BMSC medium, and BMSC±VMP medium. Ventral mesen- cephalic precursors cells were cultured in each of these media and the effects on proliferation and VMP differentiation were assessed. The relative yield of TH± cells was calculated and compared by immunocytochemical staining. RESULTS After a 7-day culture and induction of VMPs, the total cell counts were increased by （44.13±4.75）-fold （common）, （60.63±5.25）-fold （BMSC）, and （64.00±7.63）-fold （BMSC±VMP）. The proportions of TH＋ cells were （18.76±5.20）%, （23.49±4.10）%, and （28.08± 5.42）%, respectively, with statistically significant differences among the treatment groups. CONCLUSION BMSCs release factors that promote the proliferation of VMPs and facilitate the committed differentiation of VMPs into dopaminergic neurons.
基金supported by the National Natural Science Foundation of China (No. 21177106)the Bureau of Science and Technology of Zhejiang Province (No. 2007C23G2010234)the China Scholarship Council (No. 2009632081)
文摘Understanding the pattern ofphytoplankton and their dependence on water quality variables, can help the management of eutrophic lakes. The aim of this study was to determine water quality and environmental factors associated with cyanobacteria dominance and microcystin production in Qingshan Lake, a subtropical lake located in the headwater of the Taihu watershed, China. Water samples collected monthly from 10 study sites in Qingshan Lake were analyzed for the species distributions of freshwater algae and physico-chemical parameters including total nitrogen （TN）, ammonia （NH4＋-N）, nitrate （NO3--N）, total phosphorus （TP）, and chlorophyll a （Chl-a） from June, 2008 to May, 2009. Qingshan Lake was found to be eutrophic, based on the calculated trophic state index （TSI）. The average TN of 4.33 mg/L during the study period exceeded the Surface Water Quality Standards of China. TP was significantly correlated with relative abundance of cyanobacteria and Microeystis biovolume, indi- cating its important role in regulating cyanobacteria. Microcystis, Anabaena, and Oscillatoria were dominant cyanobacteria in Qingshan Lake from June to November, 2008. Cyanobacteria dominance was regulated by water temperature and TE Principal component analysis further indicated that microcystin production was most affected by water temperature, TP, and cyanobacteria biomass. Results suggest that the control of TP in summer can mitigate cyanobacteria dominance and microcystin production in Qingshan Lake, and close monitoring should be undertaken in summer.
文摘We consider a model of the exploitative competition of two micro-organisms for two complementary nutrients in a chemostat and take into account the interspecific interac- tion. The growth functions occurring in the model are of general type and the interaction functions are monotonic and positive. By the mean of the Thieme-Zhao theorem, we establish conditions for uniform persistence of the model.
基金supported by the National Natural Science Foundation of China (No.30670868)the Natural Science Foundation of Zheji-ang Province,China (No.R206007)
文摘Objective： The aim of this study was to test the protective effect of mesenchymal stem cells （MSCs） on cardiomyocytes in vitro and to investigate the anti-apoptotic signaling pathway. Methods： MSCs from Sprague-Dawley （SD） rats were separated and cultured. MSC medium was collected from MSCs （DMEM） under hypoxia. Cultured cardiomyocytes from neonatal cultured in serum-free Dulbecco＇s modified eagle medium SD rats were exposed to hypoxia/reoxygenation （H/R） and treated with MSC medium. The apoptotic cardiomyocytes were stained with Annexin-V-fluorescein isothiocyanate （FITC）, Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling （TUNEL）. The mitochondrial transmembrane potential of cardiomyocytes was assessed using a fluorescence microscope. The expression of Bcl-2, Bax, cyto- chrome C, apoptosis-induced factor （AIF）, and caspase-3 was tested by Western blot analysis. Results： Our data demonstrated that MSC medium reduced H/R-induced cardiomyocyte apoptosis, increased the Bcl-2/Bax ratio, and reduced the release of cyto- chrome C and AIF from mitochondria into the cytosol. Conclusion： MSCs protected the cardiomyocytes from H/R-induced apoptosis through a mitochondrial pathway in a paracrine manner.
文摘Aims Although increases in precipitation variability in arid ecosystems are projected due to climate change,the response of desert shrub communities to precipitation change has not been fully elucidated.Such knowledge is important since drought-adapted plants exhibit varied mechanisms of survival that may contribute to species coexistence.Methods We tested the responses of eight drought-adapted plants,a mix of graminoids,shrubs and forbs to three summer precipitation scenarios(1.3,2.6 and 3.9 cm per month)in a common garden experiment in the Great Basin(Owens Valley,California).Changes in mineral nutrient uptake(carbon,nitrogen,phosphorus,potassium,calcium,magnesium,manganese,copper,boron,zinc,iron and sodium)and gas exchange parameters(photosynthetic rate and stomatal conductance)were investigated in the studied species.Important Findings Two graminoids(Sporobolus airoides and Leymus triticoides)and one salt tolerant shrub species(Atriplex confertifolia)responded to increased water availability with increases in photosynthetic rate and/or stomatal conductance.There was a significant correlation between water availability and uptake of nutrients for five out of eight species.Artemisia tridentata,with higher rates of photosynthesis,contained greater amounts of potassium,copper and boron,while Juncus arcticus,with higher rates of photosynthesis,contained greater amounts of magnesium and iron,and less sodium.Juncus arcticus and three salt-adapted species(A.confertifolia,Distichlis spicata and S.airoides)exhibited correlations with stomatal conductance and concentrations of nutrients.Results indicate that differential physiological response mechanisms to increased moisture and associated nutrient uptake strategies in drought-adapted species may mediate coexistence under increased summer precipitation.
基金supported by the National Natural Science Foundation of China(42130515 and31770506)the Open Foundation of the State Key Laboratory of Urban and Regional Ecology of Chinathe Open Foundation of the State Key Laboratory of Grassland Agro-ecosystems of China。
文摘Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.
