To better understand the ecological and economic benefits of short-term grazing exclusion on the aboveground net primary productivity(ANPP)of alpine pastures,we conducted annual multi-site transect surveys in the summ...To better understand the ecological and economic benefits of short-term grazing exclusion on the aboveground net primary productivity(ANPP)of alpine pastures,we conducted annual multi-site transect surveys in the summers from 2009 to 2011 and calculated the aboveground biomass discrepancy(ABD)between grazed and ungrazed pastures at plant community and economic group levels for three zonal alpine grassland types—meadow,steppe,and desert-steppe—across the northern Tibetan Plateau.Our results indicated that aboveground biomass(AGB)significantly differed among grassland types and declined northwesterly from 64.07 to11.44 g m-2with decreasing precipitation and increasing temperature.The mean ABD exhibited considerable community dependency,with meadow(12.47 g m-2)[steppe(6.91 g m-2)[desert steppe(2.54 g m-2),and it declined from 25.42 to 1.29 g m-2with decreasing precipitation and increasing temperature.‘Good forage’,i.e.grasses and sedges,benefited most from grazing exclusion,followed by edible forbs.With longer grazing exclusion durations(GEDs),the aboveground biomass of poisonous locoweeds initially decreased and then increased compared with the adjacent grazed sites.In the nested analysis of co-variances with a general linear model,growing season precipitation(GSP;from May to September)accounted for 52.67%ofthe observed variation in AGB,followed by AGT(9.77%)and pasture management systems(PMSs;grazing or grazing-excluded,5.31%).The variation in ABD was explained primarily by AGT(16.52%),GED(20.25%),and the interaction of AGT 9 GED(19.58%).Our results confirm that precipitation is the primary factor controlling the ANPP of alpine grasslands on the Northern Tibetan Plateau and that the ecological benefits arising from grazing exclusion are also partly dependent on grassland type and exclusion duration.Therefore,spatial and temporal variations in growing season precipitation and plant functional traits or economic group composition should be jointly considered when developing policies concerning the management and spatial layouts of grazing exclosures in this region.展开更多
Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from th...Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from three typical grassland ecosystems in China,including a temperate semiarid steppe in Inner mongolia(Neimeng site,Nm),an alpine shrub-meadow in Qinghai(Haibei site,Hb)and an alpine meadow steppe in Tibet(Dangxiong site,DX),to examine the time lagged effects of environmental factors on CO_(2) exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands.In linking carbon fluxes with climatic factors,we used their averages or cumulative values within each 12-month period and we called them‘yearly’statistics in this study.To investigate the lagged effects of the climatic factors on the car-bon fluxes,the climatic‘yearly’statistics were kept still and the‘yearly’statistics of the carbon fluxes were shifted backward 1 month at a time.Important Findingssoil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine Hb and DX,respectively,while the Nm site was under a synthetic impact of each climatic factor.The time lagged effect analysis showed that temperature had several months,even half a year lag effects on Co2 exchange at the three studied sites,while moisture’s effects were mostly exhibited as an immediate manner,except at Nm.In general,the lagged climatic effects were relatively weak for the alpine ecosystem.our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate,so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability.an improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.展开更多
Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cot...Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cotton strips that had been buried in soil for a year were sampled at three sites at different altitudes(4500,4950 and 5200 m)located on a southeast-facing slope on the Nyainqentanglha Mountains near Damxung.The fungi on the cotton strips were isolated using a modified washing method.The decomposition abilities and colony growth properties of the major species cultured in pure-culture conditions were investigated and compared.Canonical correspondence analysis(CCA)was used to evaluate the relationships between fungal community composition and environmental variables(altitude,soil depth,soil water content[SWC],plant root mass and gravel content).Important Findings A total of 24 species were isolated from the cotton strips,and 12 species occurred frequently and were regarded as major species.The number of fungal species was lower at the 4950-m altitude site than at the other two sites,indicating that not only altitude but also other factors affected the number of species present.All of the major species were able to decompose the cotton strips.In the CCA ordination,automatic forward selection revealed that altitude,SWC and plant root mass significantly affected fungal species composition.Our results suggest thatspecies numberandthecomposition ofcellulolytic fungal communities are highly correlated with environmental variables as well as altitude in the alpine meadow on the Tibetan Plateau.展开更多
Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G^(**) basis set.Geometries obtained...Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G^(**) basis set.Geometries obtained from DFT calculations were used to perform the natural bond orbital(NBO)analysis.It is noted that weakness in the O_(3)-N_(2) bond is due to nO_(1)→σO_(3)-N_(2) delocalization and is responsible for the longer O_(3)-N_(2) bond lengths in O-nitrosyl carboxylate compounds.It is also noted that decreased occupancy of the localized σO_(3)-N_(2) orbital in the idealized Lewis structure,or increased occupancy of σO_(3)-N_(2) of the non-Lewis orbital,and their subsequent impact on molecular stability and geometry(bond lengths)are related with the resulting p character of the corresponding sulfur natural hybrid orbital(NHO)of σ_(O_(3)-N_(2)) bond orbital.In addition,the charge transfer energy decreases with the increase of the Hammett constants of subsitutent groups.展开更多
Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry,harmonic vibrational frequency along with intensities in IR and Raman spectra at RHF/6-31++G^(**)and B3LYP/6-31...Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry,harmonic vibrational frequency along with intensities in IR and Raman spectra at RHF/6-31++G^(**)and B3LYP/6-31++G^(**)levels for phenobarbitone(C12H12N2O3)in the ground state.The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman spectra.Theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions(PEDs)using MOLVIB program.A detailed interpretation of the infrared spectra of the title compound is reported.On the basis of the agreement between the calculated and observed results,the assignments of fundamental vibrational modes of phenobarbitone were examined and some assignments were proposed.The theoretical spectrograms for FT-IR and FT-Raman spectra of the title compound have been constructed.展开更多
基金supported by the National Natural Science Foundation of China(31870406,42071066)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK0302).
基金supported by the National Natural Science Foundation of China(41171044)Knowledge Innovation Project of the Chinese Academy of Sciences(XDB03030401&KZCXZ-XB3-08)by a General Financial Grant from theChina Postdoctoral Science Foundation(2013M530716)
文摘To better understand the ecological and economic benefits of short-term grazing exclusion on the aboveground net primary productivity(ANPP)of alpine pastures,we conducted annual multi-site transect surveys in the summers from 2009 to 2011 and calculated the aboveground biomass discrepancy(ABD)between grazed and ungrazed pastures at plant community and economic group levels for three zonal alpine grassland types—meadow,steppe,and desert-steppe—across the northern Tibetan Plateau.Our results indicated that aboveground biomass(AGB)significantly differed among grassland types and declined northwesterly from 64.07 to11.44 g m-2with decreasing precipitation and increasing temperature.The mean ABD exhibited considerable community dependency,with meadow(12.47 g m-2)[steppe(6.91 g m-2)[desert steppe(2.54 g m-2),and it declined from 25.42 to 1.29 g m-2with decreasing precipitation and increasing temperature.‘Good forage’,i.e.grasses and sedges,benefited most from grazing exclusion,followed by edible forbs.With longer grazing exclusion durations(GEDs),the aboveground biomass of poisonous locoweeds initially decreased and then increased compared with the adjacent grazed sites.In the nested analysis of co-variances with a general linear model,growing season precipitation(GSP;from May to September)accounted for 52.67%ofthe observed variation in AGB,followed by AGT(9.77%)and pasture management systems(PMSs;grazing or grazing-excluded,5.31%).The variation in ABD was explained primarily by AGT(16.52%),GED(20.25%),and the interaction of AGT 9 GED(19.58%).Our results confirm that precipitation is the primary factor controlling the ANPP of alpine grasslands on the Northern Tibetan Plateau and that the ecological benefits arising from grazing exclusion are also partly dependent on grassland type and exclusion duration.Therefore,spatial and temporal variations in growing season precipitation and plant functional traits or economic group composition should be jointly considered when developing policies concerning the management and spatial layouts of grazing exclosures in this region.
基金This work was supported by the 973 Program(2013CB956302)of the Ministry of Science and Technology of China,and One Hundred Talent Plan,Chinese Academy of Sciences.
文摘Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from three typical grassland ecosystems in China,including a temperate semiarid steppe in Inner mongolia(Neimeng site,Nm),an alpine shrub-meadow in Qinghai(Haibei site,Hb)and an alpine meadow steppe in Tibet(Dangxiong site,DX),to examine the time lagged effects of environmental factors on CO_(2) exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands.In linking carbon fluxes with climatic factors,we used their averages or cumulative values within each 12-month period and we called them‘yearly’statistics in this study.To investigate the lagged effects of the climatic factors on the car-bon fluxes,the climatic‘yearly’statistics were kept still and the‘yearly’statistics of the carbon fluxes were shifted backward 1 month at a time.Important Findingssoil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine Hb and DX,respectively,while the Nm site was under a synthetic impact of each climatic factor.The time lagged effect analysis showed that temperature had several months,even half a year lag effects on Co2 exchange at the three studied sites,while moisture’s effects were mostly exhibited as an immediate manner,except at Nm.In general,the lagged climatic effects were relatively weak for the alpine ecosystem.our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate,so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability.an improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.
基金Academic Frontier’Project for Private Universities:a matching fund subsidy from MEXT(Ministry of Education,Culture,Sports,Science,and Technology of Japan)2007–2010.This study was part of a joint research project between the National Institute for Environmental Studies,Japan,and the Northwest Institute of Plateau of Biology,China,and was supported by the‘Early Detection and Prediction of Climate Warming Based on the Long-Term Monitoring of Alpine Ecosystems on the Tibetan Plateau’project.
文摘Aims The aims of this study were to compare the fungal communities developing on cotton strips at three different altitudes on the Tibetan Plateau and to assess the environmental variables influencing them.Methods Cotton strips that had been buried in soil for a year were sampled at three sites at different altitudes(4500,4950 and 5200 m)located on a southeast-facing slope on the Nyainqentanglha Mountains near Damxung.The fungi on the cotton strips were isolated using a modified washing method.The decomposition abilities and colony growth properties of the major species cultured in pure-culture conditions were investigated and compared.Canonical correspondence analysis(CCA)was used to evaluate the relationships between fungal community composition and environmental variables(altitude,soil depth,soil water content[SWC],plant root mass and gravel content).Important Findings A total of 24 species were isolated from the cotton strips,and 12 species occurred frequently and were regarded as major species.The number of fungal species was lower at the 4950-m altitude site than at the other two sites,indicating that not only altitude but also other factors affected the number of species present.All of the major species were able to decompose the cotton strips.In the CCA ordination,automatic forward selection revealed that altitude,SWC and plant root mass significantly affected fungal species composition.Our results suggest thatspecies numberandthecomposition ofcellulolytic fungal communities are highly correlated with environmental variables as well as altitude in the alpine meadow on the Tibetan Plateau.
基金supported by the National Natural Science Foundation of China(31870406,41661144045)the State Key Research and Development Program(2016YFC0502001,2017YFA0604801).
文摘在温带和寒冷地区,春季植被物候的变化普遍受温度影响。然而,在寒冷地区的干旱/半干旱生态系统中,温度对物候的影响仍难以捉摸,因为土壤水分状况有调节物候的重要作用。利用生长度日(growing degree day,GDD)和生长季节指数(growing season index,GSI)模型,对最低温度(minimum daily temperature,T_(min))与土壤水分(daily soil moisture,SM)进行耦合,探索热量需求和水文气候交互作用对青藏高原(QTP)两个不同降水状况的高寒草甸生态系统碳吸收期开始日期(start of carbon uptake period,SCUP)和净生态系统初级生产力(net ecosystem productivity,NEP)的影响。其中,一种是水分限制的高寒草原草甸生态系统,另一种是温度限制的高寒灌丛草甸生态系统。GDD模型和GSI模型与SCUP明显相关联:在湿润的高寒灌丛草甸生态系统中,SCUP对生长季前GDD和GSI的变化同样敏感;而在半干旱高寒草原草甸生态系统中,与GDD相比,SCUP对生长季前GSI的变化更敏感。这些不同模式表明,限制SCUP的气候因子由温度和水分有效性的平衡来决定。在湿润的高寒草甸生态系统中,在不受干旱胁迫的情况下,较高的SCUP温度敏感性可以最大化热效益,正如观察到的SCUPs与GDD模型模拟具有较高的线性相关系数(R2)和AIC。而在半干旱的草原化草甸中,较高的SCUP水分敏感性可以最大化水分效益,正如观测到的SCUPs与GSI模型模拟具有较高的R2和AIC。此外,虽然在高寒灌丛草甸生态系统中SCUPs由GDD决定,但两个高寒草甸生态系统NEP均受累积GSI控制。本研究重点强调湿润和半干旱高寒草甸生态系统水文气候交互作用对春季碳通量物候和植被生产力的影响;揭示半干旱地区高寒草甸生态系统物候和碳平衡模型中应该包括温度和水分条件。这些结果对改善植被物候模型具有重要意义,从而加深我们对将来植被物候、生产力和气候变化相互作用的理解。
基金We gratefully thank the National Natural Science Foundation of China(Grant No.10774039)the grant from Development Program in Science and Technology of Henan Province(Grant No.102300410114)Foundation for University Key Teacher by the Ministry of Education of Henan Province,and Henan University of Science and Technology for Young Scholars(Grant No.2009QN0032)for their support of this work.
文摘Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G^(**) basis set.Geometries obtained from DFT calculations were used to perform the natural bond orbital(NBO)analysis.It is noted that weakness in the O_(3)-N_(2) bond is due to nO_(1)→σO_(3)-N_(2) delocalization and is responsible for the longer O_(3)-N_(2) bond lengths in O-nitrosyl carboxylate compounds.It is also noted that decreased occupancy of the localized σO_(3)-N_(2) orbital in the idealized Lewis structure,or increased occupancy of σO_(3)-N_(2) of the non-Lewis orbital,and their subsequent impact on molecular stability and geometry(bond lengths)are related with the resulting p character of the corresponding sulfur natural hybrid orbital(NHO)of σ_(O_(3)-N_(2)) bond orbital.In addition,the charge transfer energy decreases with the increase of the Hammett constants of subsitutent groups.
基金the National Natural Science Foundation of China(Grant No.10774039)the Development Program in Science and Technology of Henan Province(No.102300410114)Henan University of Science and Technology for Young Scholars(No.2009QN0032)for their support of this work.
文摘Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry,harmonic vibrational frequency along with intensities in IR and Raman spectra at RHF/6-31++G^(**)and B3LYP/6-31++G^(**)levels for phenobarbitone(C12H12N2O3)in the ground state.The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman spectra.Theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions(PEDs)using MOLVIB program.A detailed interpretation of the infrared spectra of the title compound is reported.On the basis of the agreement between the calculated and observed results,the assignments of fundamental vibrational modes of phenobarbitone were examined and some assignments were proposed.The theoretical spectrograms for FT-IR and FT-Raman spectra of the title compound have been constructed.