We examined the global biogeography of the Scytodes thoracica group of spitting spiders based on 23 years of sampling at the species level(61 species in the thoracica group and 84 species of Scytodes)using DNA data fr...We examined the global biogeography of the Scytodes thoracica group of spitting spiders based on 23 years of sampling at the species level(61 species in the thoracica group and 84 species of Scytodes)using DNA data from six loci.Our results indicated that the thoracica group initially dispersed from Southeast Asia to East Africa between 46.5 and 33.0 million years ago,and dispersal events intensified between Southeast/South Asia and East/South Africa from the early to late Miocene.The timing of these events indicates that Asian-African faunal exchange of the thoracica group was driven by the Indian monsoon,and the pattern of dispersal suggests that colonialization took root when the Indian monsoon shifted from a North-South direction to an East-West direction from the middle Eocene.展开更多
Investigation of the climate change effects on drought is required to develop management strategies for minimizing adverse social and economic impacts.Therefore,studying the future meteorological drought conditions at...Investigation of the climate change effects on drought is required to develop management strategies for minimizing adverse social and economic impacts.Therefore,studying the future meteorological drought conditions at a local scale is vital.In this study,we assessed the efficiency of seven downscaled Global Climate Models(GCMs)provided by the NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP),and investigated the impacts of climate change on future meteorological drought using Standard Precipitation Index(SPI)in the Karoun River Basin(KRB)of southwestern Iran under two Representative Concentration Pathway(RCP)emission scenarios,i.e.,RCP4.5 and RCP8.5.The results demonstrated that SPI estimated based on the Meteorological Research Institute Coupled Global Climate Model version 3(MRI-CGCM3)is consistent with the one estimated by synoptic stations during the historical period(1990-2005).The root mean square error(RMSE)value is less than 0.75 in 77%of the synoptic stations.GCMs have high uncertainty in most synoptic stations except those located in the plain.Using the average of a few GCMs to improve performance and reduce uncertainty is suggested by the results.The results revealed that with the areas affected by wetness decreasing in the KRB,drought frequency in the North KRB is likely to increase at the end of the 21st century under RCP4.5 and RCP8.5 scenarios.At the seasonal scale,the decreasing trend for SPI in spring,summer,and winter shows a drought tendency in this region.The climate-induced drought hazard can have vast consequences,especially in agriculture and rural livelihoods.Accordingly,an increasing trend in drought during the growing seasons under RCP scenarios is vital for water managers and farmers to adopt strategies to reduce the damages.The results of this study are of great value for formulating sustainable water resources management plans affected by climate change.展开更多
Aims Fire and atmospheric nitrogen(N)deposition have the potential to influence growth and productivity of forest canopy.However,their impacts on photosynthesis and growth traits of understory plants in forests remain...Aims Fire and atmospheric nitrogen(N)deposition have the potential to influence growth and productivity of forest canopy.However,their impacts on photosynthesis and growth traits of understory plants in forests remain largely unexplored.This study was conducted to examine the effects of burning and N addition on foliar N content,net photosynthesis and growth traits of three dominant shrub species(Vitex negundo,Lindera glauca and Symplocos chinensis)in a temperate forest in Central China.Methods The experiment used a pair-nested design,with four treatments(control,burning,N addition and burning plus N addition)and five replicates.Leaf mass area(LMA),area-based concentrations of foliar N and chlorophyll(N_(area) and Chl_(area)),net photosynthesis(A_(n)),stomatal conductance(g_(s)),maximum photosynthetic rate(A_(max))and maximal carboxylation rate(V_(cmax)),basal diameter,height and branch length(BL)of the three species were measured.Important Findings Across the three species,burning stimulated LMA,N_(area),Chl_(area),A_(n),g_(s),A_(max) and V_(cmax),and consequently enhanced basal diam-eter,height and BL.Nitrogen addition increased A_(n) and gs but did not affect LMA,N_(area),Chl_(area),A_(max),V_(cmax),basal diameter,height or BL.However,N addition strengthened the positive effects of burning on g_(s),V_(cmax),A_(n) and BL.The findings indicate the primary role of light resources in determining plant photosynthesis and growth of understory shrub species after fire and highlight that understory plants should be considered in projection of biomass accumulation and productivity of forests under environmental perturbations.展开更多
Aims Ecosystem carbon models often require accurate net ecosystem exchange of CO_(2)(NEE)light-response parameters,which can be derived from the Michaelis–Menten equation.These parameters include maximum net ecosyste...Aims Ecosystem carbon models often require accurate net ecosystem exchange of CO_(2)(NEE)light-response parameters,which can be derived from the Michaelis–Menten equation.These parameters include maximum net ecosystem exchange(NEE_(max)),apparent quantum use efficiency(a)and daytime ecosystem respiration rate(R_(e)).However,little is known about the effects of land conversion between steppe and cropland on these parameters,especially in semi-arid regions.To understand how these parameters vary in responses to biotic and abiotic factors under land conversions,seasonal variation of light-response parameters were evaluated for a steppe and a cropland of Inner Mongolia,China,during three consecutive years(2006–08)with different precipitation amounts.Methods NEE was measured over a steppe and a cropland in Duolun,Inner Mongolia,China,using the eddy covariance technique,and NEE light-response parameters(NEE_(max),α and R_(e))were derived using the Michaelis–Menten model.Biophysical regulations of these parameters were evaluated using a stepwise regression analysis.Important Findings The maximum absolute values of NEE_(max) occurred in the meteorological regimes of 15℃<T_(a)<25℃,vapor pressure deficit(VPD)<1 KPa and 0.21 m^(3) m^(-3)<volumetric soil water content at 10 cm(SWC)<0.28 m^(3) m^(-3) for both the steppe and the cropland ecosystems.The variations of α and R_(e) showed no regular variation pattern in different T_(air),VPD and SWC regimes.Under the same regime of T_(air),VPDand SWC,the cropland had higher absolute values of NEE_(max) than the steppe.Canopy conductance and leaf area index(LAI)were dominant drivers for variations in NEE light-response parameters of the steppe and the cropland.The seasonal variation of NEE light-response parameters followed the variation of LAI for two ecosystems.The peak values of all light-response parameters for the steppe and the cropland occurred fromJuly to August.The values of NEE light-response parameters(NEE_(max),α and R_(e))were lower in the driest year(2007展开更多
Social responses to climate change over human history have been widely discussed in academia over the last two decades. However, the transformation of the human–environment nexus crossing prehistoric and historic per...Social responses to climate change over human history have been widely discussed in academia over the last two decades. However, the transformation of the human–environment nexus crossing prehistoric and historic periods and the processes associated with it are not yet clearly understood. In this study, based on published works on radiocarbon dating, archaeobotany, zooarchaeology, and archaeological sites, together with a synthesis of historical documents and highresolution paleoclimatic records, we trace the extent to which human settlement patterns in the Hexi Corridor in northwestern China evolved in conjunction with climate change over the last 5,000 years. A total of 129 Neolithic, 126 Bronze Age, and 1,378 historical sites in the Hexi Corridor(n=1,633) were surveyed. Our results show that, in the Late Neolithic and Bronze Age periods(~2800–100 BC), climate change contributed to the transformation of subsistence strategies and the subsequent changes in human settlement patterns in the Hexi Corridor. The warm-humid climate in ~2800–2000 BC promoted millet agriculture and helped the Majiayao, Banshan, and Machang Cultures to flourish. The cold-dry climate in ~2000–100 BC resulted in the divergence and transformation of subsistence strategies in the Xichengyi–Qijia–Siba and Shajing–Shanma Cultures and in a shift in their settlement patterns. However, in the historical period(121 BC–AD 1911), human settlement patterns were primarily determined by geopolitics related to the alternating rule of regimes and frequent wars, especially in the Sui–Tang dynasties. We also find that trans-Eurasian cultural exchange since ~2000 BC improved social resilience to climate change in the Hexi Corridor, mediating the human–environment nexus there. Our findings may provide insights into how human societies reacted to climate change in arid and semi-arid environments over the long term.展开更多
The‘‘dynamic knowledge loop’’explores processes of knowledge generation,knowledge exchange,and social learning in inter-and transdisciplinary cooperation and relates them to adaptive capacity.Adaptive capacity bui...The‘‘dynamic knowledge loop’’explores processes of knowledge generation,knowledge exchange,and social learning in inter-and transdisciplinary cooperation and relates them to adaptive capacity.Adaptive capacity building can reduce vulnerabilities and enhance the resilience of urban regions towards the impacts of climate change.We use a mix of empirical methods and apply the dynamic knowledge loop as an innovative analytical tool.The added value of inter-and transdisciplinary cooperation concerning knowledge generation and facilitation of social learning is discussed by applying the dynamic knowledge loop to research about a scenario-planning process and a participatory mapping exercise in the urban region of Rostock,Germany.The results demonstrate that the scenario planning process allowed for a consideration of complex interrelations that have the potential for an integration of different influences,perspectives,and knowledge forms.Scenario planning facilitated social learning by creating a platform for integration and exchange of different epistemologies and for considering alternative futures.The participatory mapping exercise demonstrated the scientific value of the integration of local knowledge as well.Building upon these results,we stress the importance of knowledge generation,knowledge exchange,and social learning to build up adaptive capacity through different forms of cooperation between science and practice.展开更多
Forecasting environmental parameters in the distant future requires complex modelling and large computational resources.Due to the sensitivity and complexity of forecast models,long-term parameter forecasts(e.g.up to ...Forecasting environmental parameters in the distant future requires complex modelling and large computational resources.Due to the sensitivity and complexity of forecast models,long-term parameter forecasts(e.g.up to 2100)are uncommon and only produced by a few organisations,in heterogeneous formats and based on different assumptions of greenhouse gases emissions.However,data mining techniques can be used to coerce the data to a uniform time and spatial representation,which facilitates their use in many applications.In this paper,streams of big data coming from AquaMaps and NASA collections of 126 long-term forecasts of nine types of environmental parameters are processed through a cloud computing platform in order to(i)standardise and harmonise the data representations,(ii)produce intermediate scenarios and new informative parameters,and(iii)align all sets on a common time and spatial resolution.Time series crosscorrelation applied to these aligned datasets reveals patterns of climate change and similarities between parameter trends in 10 marine areas.Our results highlight that(i)the Mediterranean Sea may have a standalone‘response’to climate change with respect to other areas,(ii)the Poles are most representative of global forecasted change,and(iii)the trends are generally alarming for most oceans.展开更多
In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The f...In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.展开更多
The palaeo-atmospheric CO2 concentration （pCOz） variation in the Yumen, Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic mo...The palaeo-atmospheric CO2 concentration （pCOz） variation in the Yumen, Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic model, and the results show that the pCO2 values are in the range of about 550 -808 ppmv. The present pCO2 values are higher than the pCO2 results （531-641 ppmv） of the previous study according to the Recent standardization of the stomatal ratio method, and much lower than the pCO2 results （882-1060 ppmv） according to the Carboniferous standardization of the stomatal ratio method. The present pCOz variation is not only within the error range of GEOCARB II and GEOCARB Ill but also is similar to the reconstructed results based on the biochemistry and carbon isotope models. Besides, the present Brachyphyllum specimens were collected from four consecutive horizons of the upper Zhonggou Formation of the Hanxia Section, and the reconstructed pCO2 exhibits the reconstructed pCO2 exhibits a decline trend during the late Aptian to early Albian. This decline variation is probably associated with the Oceanic Anoxic Events （OAElb） and the Cold snap event. With the combination of pCO2 during the Albian to Cenomanian recovered by the plant photosynthetic gas exchange mechanistic model, the pCO2 showed a prominent increase during the late Aptian to early Cenominian, which indicates a response to the greenhouse warming during the middle Cretaceous. Therefore, the mechanical model of the plant photosynthetic gas exchange shows a relatively strong accuracy in the reconstruction of thepCO2 and can reflect a strong relation between the atmospheric CO2 concentrations and climatic events.展开更多
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences to S.Q.L.(XDB31000000)National Natural Sciences Foundation of China to Y.F.L.(NSFC-31860602,32170463,31660611)。
文摘We examined the global biogeography of the Scytodes thoracica group of spitting spiders based on 23 years of sampling at the species level(61 species in the thoracica group and 84 species of Scytodes)using DNA data from six loci.Our results indicated that the thoracica group initially dispersed from Southeast Asia to East Africa between 46.5 and 33.0 million years ago,and dispersal events intensified between Southeast/South Asia and East/South Africa from the early to late Miocene.The timing of these events indicates that Asian-African faunal exchange of the thoracica group was driven by the Indian monsoon,and the pattern of dispersal suggests that colonialization took root when the Indian monsoon shifted from a North-South direction to an East-West direction from the middle Eocene.
文摘Investigation of the climate change effects on drought is required to develop management strategies for minimizing adverse social and economic impacts.Therefore,studying the future meteorological drought conditions at a local scale is vital.In this study,we assessed the efficiency of seven downscaled Global Climate Models(GCMs)provided by the NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP),and investigated the impacts of climate change on future meteorological drought using Standard Precipitation Index(SPI)in the Karoun River Basin(KRB)of southwestern Iran under two Representative Concentration Pathway(RCP)emission scenarios,i.e.,RCP4.5 and RCP8.5.The results demonstrated that SPI estimated based on the Meteorological Research Institute Coupled Global Climate Model version 3(MRI-CGCM3)is consistent with the one estimated by synoptic stations during the historical period(1990-2005).The root mean square error(RMSE)value is less than 0.75 in 77%of the synoptic stations.GCMs have high uncertainty in most synoptic stations except those located in the plain.Using the average of a few GCMs to improve performance and reduce uncertainty is suggested by the results.The results revealed that with the areas affected by wetness decreasing in the KRB,drought frequency in the North KRB is likely to increase at the end of the 21st century under RCP4.5 and RCP8.5 scenarios.At the seasonal scale,the decreasing trend for SPI in spring,summer,and winter shows a drought tendency in this region.The climate-induced drought hazard can have vast consequences,especially in agriculture and rural livelihoods.Accordingly,an increasing trend in drought during the growing seasons under RCP scenarios is vital for water managers and farmers to adopt strategies to reduce the damages.The results of this study are of great value for formulating sustainable water resources management plans affected by climate change.
基金This work was financially supported by the National Natural Science Foundation of China(31430015).
文摘Aims Fire and atmospheric nitrogen(N)deposition have the potential to influence growth and productivity of forest canopy.However,their impacts on photosynthesis and growth traits of understory plants in forests remain largely unexplored.This study was conducted to examine the effects of burning and N addition on foliar N content,net photosynthesis and growth traits of three dominant shrub species(Vitex negundo,Lindera glauca and Symplocos chinensis)in a temperate forest in Central China.Methods The experiment used a pair-nested design,with four treatments(control,burning,N addition and burning plus N addition)and five replicates.Leaf mass area(LMA),area-based concentrations of foliar N and chlorophyll(N_(area) and Chl_(area)),net photosynthesis(A_(n)),stomatal conductance(g_(s)),maximum photosynthetic rate(A_(max))and maximal carboxylation rate(V_(cmax)),basal diameter,height and branch length(BL)of the three species were measured.Important Findings Across the three species,burning stimulated LMA,N_(area),Chl_(area),A_(n),g_(s),A_(max) and V_(cmax),and consequently enhanced basal diam-eter,height and BL.Nitrogen addition increased A_(n) and gs but did not affect LMA,N_(area),Chl_(area),A_(max),V_(cmax),basal diameter,height or BL.However,N addition strengthened the positive effects of burning on g_(s),V_(cmax),A_(n) and BL.The findings indicate the primary role of light resources in determining plant photosynthesis and growth of understory shrub species after fire and highlight that understory plants should be considered in projection of biomass accumulation and productivity of forests under environmental perturbations.
基金National Basic Research Program of China(973 program)(2010CB833501)the National Natural Science Foundation of China(30800141)+1 种基金the LCLUC Program of the National Aeronautics and Space Administration(NN-H-04-Z-YS-005-N)the US-China Carbon Consortium,which promotes collaborative research among institutions in the USA and China.
文摘Aims Ecosystem carbon models often require accurate net ecosystem exchange of CO_(2)(NEE)light-response parameters,which can be derived from the Michaelis–Menten equation.These parameters include maximum net ecosystem exchange(NEE_(max)),apparent quantum use efficiency(a)and daytime ecosystem respiration rate(R_(e)).However,little is known about the effects of land conversion between steppe and cropland on these parameters,especially in semi-arid regions.To understand how these parameters vary in responses to biotic and abiotic factors under land conversions,seasonal variation of light-response parameters were evaluated for a steppe and a cropland of Inner Mongolia,China,during three consecutive years(2006–08)with different precipitation amounts.Methods NEE was measured over a steppe and a cropland in Duolun,Inner Mongolia,China,using the eddy covariance technique,and NEE light-response parameters(NEE_(max),α and R_(e))were derived using the Michaelis–Menten model.Biophysical regulations of these parameters were evaluated using a stepwise regression analysis.Important Findings The maximum absolute values of NEE_(max) occurred in the meteorological regimes of 15℃<T_(a)<25℃,vapor pressure deficit(VPD)<1 KPa and 0.21 m^(3) m^(-3)<volumetric soil water content at 10 cm(SWC)<0.28 m^(3) m^(-3) for both the steppe and the cropland ecosystems.The variations of α and R_(e) showed no regular variation pattern in different T_(air),VPD and SWC regimes.Under the same regime of T_(air),VPDand SWC,the cropland had higher absolute values of NEE_(max) than the steppe.Canopy conductance and leaf area index(LAI)were dominant drivers for variations in NEE light-response parameters of the steppe and the cropland.The seasonal variation of NEE light-response parameters followed the variation of LAI for two ecosystems.The peak values of all light-response parameters for the steppe and the cropland occurred fromJuly to August.The values of NEE light-response parameters(NEE_(max),α and R_(e))were lower in the driest year(2007
基金This study was supported by the National key R&D Program of China(Grant 2018YFA0606402)the Strategic Priority Research Program of Chinese Academy of Sciences,Pan-Third Pole,Environment Study for a Green Silk Road(Pan-TPE)(grant no.XDA20040101)+2 种基金the second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.SQ2019QZKK2201)the Improvement on Competitiveness in Hiring New Faculties Funding Scheme(4930900)Direct Grant for Research 2018/19(4052199)of the Chinese University of Hong Kong.
文摘Social responses to climate change over human history have been widely discussed in academia over the last two decades. However, the transformation of the human–environment nexus crossing prehistoric and historic periods and the processes associated with it are not yet clearly understood. In this study, based on published works on radiocarbon dating, archaeobotany, zooarchaeology, and archaeological sites, together with a synthesis of historical documents and highresolution paleoclimatic records, we trace the extent to which human settlement patterns in the Hexi Corridor in northwestern China evolved in conjunction with climate change over the last 5,000 years. A total of 129 Neolithic, 126 Bronze Age, and 1,378 historical sites in the Hexi Corridor(n=1,633) were surveyed. Our results show that, in the Late Neolithic and Bronze Age periods(~2800–100 BC), climate change contributed to the transformation of subsistence strategies and the subsequent changes in human settlement patterns in the Hexi Corridor. The warm-humid climate in ~2800–2000 BC promoted millet agriculture and helped the Majiayao, Banshan, and Machang Cultures to flourish. The cold-dry climate in ~2000–100 BC resulted in the divergence and transformation of subsistence strategies in the Xichengyi–Qijia–Siba and Shajing–Shanma Cultures and in a shift in their settlement patterns. However, in the historical period(121 BC–AD 1911), human settlement patterns were primarily determined by geopolitics related to the alternating rule of regimes and frequent wars, especially in the Sui–Tang dynasties. We also find that trans-Eurasian cultural exchange since ~2000 BC improved social resilience to climate change in the Hexi Corridor, mediating the human–environment nexus there. Our findings may provide insights into how human societies reacted to climate change in arid and semi-arid environments over the long term.
基金The research is funded by the HafenCity University and the German Federak Ministry of Research and Education through the Social–Ecological Research Programme(FKZ 01UU0909).
文摘The‘‘dynamic knowledge loop’’explores processes of knowledge generation,knowledge exchange,and social learning in inter-and transdisciplinary cooperation and relates them to adaptive capacity.Adaptive capacity building can reduce vulnerabilities and enhance the resilience of urban regions towards the impacts of climate change.We use a mix of empirical methods and apply the dynamic knowledge loop as an innovative analytical tool.The added value of inter-and transdisciplinary cooperation concerning knowledge generation and facilitation of social learning is discussed by applying the dynamic knowledge loop to research about a scenario-planning process and a participatory mapping exercise in the urban region of Rostock,Germany.The results demonstrate that the scenario planning process allowed for a consideration of complex interrelations that have the potential for an integration of different influences,perspectives,and knowledge forms.Scenario planning facilitated social learning by creating a platform for integration and exchange of different epistemologies and for considering alternative futures.The participatory mapping exercise demonstrated the scientific value of the integration of local knowledge as well.Building upon these results,we stress the importance of knowledge generation,knowledge exchange,and social learning to build up adaptive capacity through different forms of cooperation between science and practice.
基金This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the BlueBRIDGE project[grant agreement no 675680].
文摘Forecasting environmental parameters in the distant future requires complex modelling and large computational resources.Due to the sensitivity and complexity of forecast models,long-term parameter forecasts(e.g.up to 2100)are uncommon and only produced by a few organisations,in heterogeneous formats and based on different assumptions of greenhouse gases emissions.However,data mining techniques can be used to coerce the data to a uniform time and spatial representation,which facilitates their use in many applications.In this paper,streams of big data coming from AquaMaps and NASA collections of 126 long-term forecasts of nine types of environmental parameters are processed through a cloud computing platform in order to(i)standardise and harmonise the data representations,(ii)produce intermediate scenarios and new informative parameters,and(iii)align all sets on a common time and spatial resolution.Time series crosscorrelation applied to these aligned datasets reveals patterns of climate change and similarities between parameter trends in 10 marine areas.Our results highlight that(i)the Mediterranean Sea may have a standalone‘response’to climate change with respect to other areas,(ii)the Poles are most representative of global forecasted change,and(iii)the trends are generally alarming for most oceans.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41305066 and 91125016)the Special Funds for Public Welfare of China (Grant No. GYHY201306045)
文摘In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.
基金the National Natural Science Foundation of China(No.41402007,41602023,40972025)the State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,CAS(No.153102)
文摘The palaeo-atmospheric CO2 concentration （pCOz） variation in the Yumen, Gansu Province during the middle Cretaceous has been reconstructed using the newly established plant photosynthetic gas exchange mechanistic model, and the results show that the pCO2 values are in the range of about 550 -808 ppmv. The present pCO2 values are higher than the pCO2 results （531-641 ppmv） of the previous study according to the Recent standardization of the stomatal ratio method, and much lower than the pCO2 results （882-1060 ppmv） according to the Carboniferous standardization of the stomatal ratio method. The present pCOz variation is not only within the error range of GEOCARB II and GEOCARB Ill but also is similar to the reconstructed results based on the biochemistry and carbon isotope models. Besides, the present Brachyphyllum specimens were collected from four consecutive horizons of the upper Zhonggou Formation of the Hanxia Section, and the reconstructed pCO2 exhibits the reconstructed pCO2 exhibits a decline trend during the late Aptian to early Albian. This decline variation is probably associated with the Oceanic Anoxic Events （OAElb） and the Cold snap event. With the combination of pCO2 during the Albian to Cenomanian recovered by the plant photosynthetic gas exchange mechanistic model, the pCO2 showed a prominent increase during the late Aptian to early Cenominian, which indicates a response to the greenhouse warming during the middle Cretaceous. Therefore, the mechanical model of the plant photosynthetic gas exchange shows a relatively strong accuracy in the reconstruction of thepCO2 and can reflect a strong relation between the atmospheric CO2 concentrations and climatic events.
