Swidden agriculture is an age-old, widespread but controversial farming practice in Montane Mainland Southeast Asia （MMSEA）. In the uplands of northern Laos, swidden ag- riculture has remained a predominant human-do...Swidden agriculture is an age-old, widespread but controversial farming practice in Montane Mainland Southeast Asia （MMSEA）. In the uplands of northern Laos, swidden ag- riculture has remained a predominant human-dominated land-use type for centuries. However swidden system has undergone dramatic transformations since the mid-1990s. Debates on changes in swidden cultivation are linked to globally critical issues, such as land use/cover changes （LUCC）, biodiversity loss and environmental degradation. Since the implementation of Reducing Emissions from Deforestation and Forest Degradation （REDD）, much attention has been paid nationally and internationally to swidden agriculture in the tropics. However, knowledge of the explicitly spatial characteristics of swidden agriculture and the conse- quences of these transitions at macroscopic scale is surprisingly scarce. In this study, the intensity of swidden use and fallow forest recovery in northern Laos in 1990, 2002, and 2011 were delineated by means of Landsat Thematic Mapper （TM） and Enhanced Thematic Mapper plus （ETM＋） imagery （30 m） using a decision tree classification approach, followed by an analysis of the spatio-temporal changes in swidden agriculture. Next, annual successive TM/ETM＋ images during 2000-2010 were used to delineate the dynamics of the burning and cropping phase. Subsequently, the burned pixels identified in 2000 were compared respectively with their counterparts in the following years （2001-2011） to investigate temporal trends, land-use frequency, and the swidden cycle using time-series Landsat-based Normalized Difference Vegetation Index （NDVI） data. Finally, as the swidden cycle changed from 1 to 11 years, the fallow vegetation recovery process was studied. The results showed that： （1） from 1990 to 2011, the area of swidden agriculture increased by 54.98%, from 1.54× 10^5 ha to 2.38×10^5 ha in northern Laos. The increased swidden cultivation area was mainly distributed in Luang Prabang and southern B展开更多
Terrestrial ecosystem water use efficiency(WUE)is an important indicator for coupling plant photosynthesis and transpiration,and is also a key factor linking the carbon and water cycles between the land and atmosphere...Terrestrial ecosystem water use efficiency(WUE)is an important indicator for coupling plant photosynthesis and transpiration,and is also a key factor linking the carbon and water cycles between the land and atmosphere.However,under the combination of climate change and human intervention,the change in WUE is still unclear,especially on the Tibetan Plateau(TP).Therefore,satellite remote sensing data and process-based terrestrial biosphere models(TBMs)are used in this study to investigate the spatiotemporal variations of WUE over the TP from 2001 to 2010.Then,the effects of land use and land cover change(LULCC)and CO_(2) fertilization on WUE from 1981-2010 are assessed using TBMs.Results show that climate change is the leading contributor to the change in WUE on the TP,and temperature is the most important factor.LULCC makes a negative contribution to WUE(-20.63%),which is greater than the positive contribution of CO_(2) fertilization(11.65%).In addition,CO_(2) fertilization can effectively improve ecosystem resilience on the TP.On the northwest plateau,the effects of LULCC and CO_(2) fertilization on WUE are more pronounced during the driest years than the annual average.These findings can help researchers understand the response of WUE to climate change and human activity and the coupling of the carbon and water cycles over the TP.展开更多
The IPCC SRES narratives were implemented in IMAGE 2.2 to evaluate thefuture condition of the climate system (including the biosphere). A series of scenario experiments was used to assess possible ranges in emissions ...The IPCC SRES narratives were implemented in IMAGE 2.2 to evaluate thefuture condition of the climate system (including the biosphere). A series of scenario experiments was used to assess possible ranges in emissions and concentrations of greenhouse gases, climate change and impacts. These experiments focussed on the role of the terrestrial carbon cycle. The experiments show that the SRES narratives dominate human emissions and not natural processes. In contrary, atmospheric CO2 concentration strongly differs between the experiments. Atmospheric CO2 concentrations range for A1B from 714 to 1009 ppmv CO2 in 2100. The spread of this range is comparable with the full SRES range as implemented in IMAGE 2.2 (515-895 μmol/mol CO2). The most important negative and positive feedback processes in IMAGE 2.2 on the build-up of CO2 concentrations are CO2 fertilisation and soil respiration respectively. Indirect effects of these processes furtherchange land-use patterns, deforestation rates and alter the natural C fluxes. The cumulative effects of these changes have a pronounced influence on the final CO2 concentrations. Our scenario experiments highlight the importance of a proper parameterisation of feedback processes, C-cycle and land use in determining the future states of the climate system.展开更多
Soil respiration is a key component of the global carbon cycle, and even small changes in soil respiration rates could result in significant changes in atmospheric CO_2 levels. The conversion of tropical forests to ru...Soil respiration is a key component of the global carbon cycle, and even small changes in soil respiration rates could result in significant changes in atmospheric CO_2 levels. The conversion of tropical forests to rubber plantations in SE Asia is increasingly common, and there is a need to understand the impacts of this land-use change on soil respiration in order to revise CO_2 budget calculations. This study focused on the spatial variability of soil respiration along a slope in a natural tropical rainforest and a terraced rubber plantation in Xishuangbanna, Southwest(SW) China. In each land-use type, we inserted 105 collars for soil respiration measurements.Research was conducted over one year in Xishuangbanna during May, June, July and October 2015(wet season) and January and March 2016(dry season). The mean annual soil respiration rate was 30% higher in natural forest than in rubber plantation and mean fluxes in the wet and dry season were 15.1 and 9.5 Mg C ha^(-1) yr^(-1) in natural forest and 11.7 and 5.7 Mg C ha^(-1) yr^(-1) in rubber plantation. Using a linear mixedeffects model to assess the effect of changes in soil temperature and moisture on soil respiration, we found that soil temperature was the main driver of variation in soil respiration, explaining 48% of its seasonal variation in rubber plantation and 30% in natural forest. After including soil moisture, the model explained 70% of the variation in soil respiration in natural forest and 76% in rubber plantation. In the natural forest slope position had a significant effect on soil respiration, and soil temperature and soil moisture gradients only partly explained this correlation. In contrast, soil respiration in rubber plantation was not affected by slope position, which may be due to the terrace structure that resulted in more homogeneous environmental conditions along the slope. Further research is needed to determine whether or not these findings hold true at a landscape level.展开更多
Microbial carbon use efficiency(CUE)affects the soil C cycle to a great extent,but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood.In the current s...Microbial carbon use efficiency(CUE)affects the soil C cycle to a great extent,but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood.In the current study,microcosms were used to investigate how microbial respiration,biomass,and CUE responded to biotic and abiotic factors in natural tropical,subtropical,and temperate forests.Soil samples from the forests were collected,sterilized,and populated with one or a combination of three types of soil organisms(the fungus Botrytis cinerea,the bacterium Escherichia coli,and the nematode Caenorhabditis elegans).The microcosms were then kept at the mean soil temperatures of the corresponding forests.Microbial respiration,biomass,and CUE were measured over one-month incubation period.The results showed that microbial biomass and CUE were significantly higher,but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil.Biotic factors mainly affected CUE by their effect on microbial biomass,while temperature affected CUE by altering respiration.Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass,respiration,and CUE,which would provide a basis for understanding the soil C cycle in forest ecosystems.展开更多
1 Background THE C<sub>i</sub>/C<sub>a</sub>, the ratio of intercellular and ambient C0<sub>2</sub> partial pressure, is internally controlled by thestomatal conductance and assimil...1 Background THE C<sub>i</sub>/C<sub>a</sub>, the ratio of intercellular and ambient C0<sub>2</sub> partial pressure, is internally controlled by thestomatal conductance and assimilation rate, and is externally affected by the atmospheric CO<sub>2</sub> concentration and climate changes. C<sub>i</sub>/C<sub>a</sub> can be only estimated by the isotopic fractionation equation of Farquchar. However, this method is limited by the very little observation of atmospheric δ<sup>13</sup> C before1980. Leavitt had to interpolate the atmospheric δ<sup>13</sup> C by means of the polynomial. A geochemicalmethod to model C<sub>i</sub>/C<sub>a</sub> by tree-ring δ<sup>13</sup>C has been developed to reduce the dependence. By the estimated tree-ring C<sub>i</sub>/ C<sub>a</sub>, the authors here discuss C0<sub>2</sub> and water exchanges between the atmosphere and biosphere that greatly influence the climate展开更多
It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn.However,this study challenges this consensus by comparing photosynthetic capability of terre...It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn.However,this study challenges this consensus by comparing photosynthetic capability of terrestrial vegetation between the spring and autumn seasons based on measurements of 100 in situ eddy covariance towers over global extratropical ecosystems.At the majority of these sites,photosynthetic capability,indicated by light use efficiency(LUE)and apparent quantum efficiency,is significantly higher in autumn than in spring,due to lower atmosphere vapor pressure deficit(VPD)at the same air temperature.Seasonal VPD differences also substantially explain the interannual variability of the differences in photosynthetic capability between spring and autumn.We further reveal that VPD in autumn is significantly lower than in spring over 74.14% of extratropical areas,based on a global climate dataset.In contrast,LUE derived from a data-driven vegetation production dataset is significantly higher in autumn in over 61.02% of extratropical vegetated areas.Six Earth system models consistently projected continuous larger VPD values in spring compared with autumn,which implies that the impacts on vegetation growth will long exist and should be adequately considered when assessing the seasonal responses of terrestrial ecosystems to future climate conditions.展开更多
Environmental changes significantly alter the structure,diversity and activity of soil microbial communities during spring freezing-thawing period,leading to changes in the soil microbial nitrogen cycle.Changes in N_(...Environmental changes significantly alter the structure,diversity and activity of soil microbial communities during spring freezing-thawing period,leading to changes in the soil microbial nitrogen cycle.Changes in N_(2)O fluxes after land use conversion from primary forest to secondary forest,Korean pine plantation and cropland in northeast China have not been quantified.Field experiments were conducted to measure soil N_(2)O fluxes in a primary forest,two secondary forests,a Korean pine plantation,and one maize field in a temperate region in northeast China from 2017-03-06 to 2017-05-28.During the experimental period,the soil was exclusively a nitrogen source for all land uses.We found that N_(2)O emissions ranged from 15.63 to 68.74μg m^(-2) h^(-1),and cumulative N_(2)O emissions ranged from 0.33 to 2.10 kg ha^(-1) during the period.Cumulative N_(2)O emissions from the maize field were significantly higher than that from primary forest,Korean pine plantation,hardwood forest,and Betula platyphylla forest by 262.1% to 536.4%.Compared with other ecosystems in similar studies,the N_(2)O emission rates of all ecosystem types in this study were low during the spring thaw period.Stepwise multiple linear regression indicated that there were significant correlations between N_(2)O emissions and environmental factors(air temperature and soil temperature,soil water content,soil p H,NH_(4)^(+)-N,NO_(3)^(-)-N,and soil organic carbon).The results showed that conversion of land use from primary forest to hardwood forest,Korean pine plantation or maize field greatly increased soil N_(2)O emissions during spring freezing-thawing period,and N_(2)O emissions from primary forest were almost the same as those from Betula platyphylla forest.展开更多
基金National Natural Science Foundation of China, No.41301090, No.41271117 Key Program for Strategic Science and Technology, Chinese Academy of Sciences, No.2014SJCB006
文摘Swidden agriculture is an age-old, widespread but controversial farming practice in Montane Mainland Southeast Asia （MMSEA）. In the uplands of northern Laos, swidden ag- riculture has remained a predominant human-dominated land-use type for centuries. However swidden system has undergone dramatic transformations since the mid-1990s. Debates on changes in swidden cultivation are linked to globally critical issues, such as land use/cover changes （LUCC）, biodiversity loss and environmental degradation. Since the implementation of Reducing Emissions from Deforestation and Forest Degradation （REDD）, much attention has been paid nationally and internationally to swidden agriculture in the tropics. However, knowledge of the explicitly spatial characteristics of swidden agriculture and the conse- quences of these transitions at macroscopic scale is surprisingly scarce. In this study, the intensity of swidden use and fallow forest recovery in northern Laos in 1990, 2002, and 2011 were delineated by means of Landsat Thematic Mapper （TM） and Enhanced Thematic Mapper plus （ETM＋） imagery （30 m） using a decision tree classification approach, followed by an analysis of the spatio-temporal changes in swidden agriculture. Next, annual successive TM/ETM＋ images during 2000-2010 were used to delineate the dynamics of the burning and cropping phase. Subsequently, the burned pixels identified in 2000 were compared respectively with their counterparts in the following years （2001-2011） to investigate temporal trends, land-use frequency, and the swidden cycle using time-series Landsat-based Normalized Difference Vegetation Index （NDVI） data. Finally, as the swidden cycle changed from 1 to 11 years, the fallow vegetation recovery process was studied. The results showed that： （1） from 1990 to 2011, the area of swidden agriculture increased by 54.98%, from 1.54× 10^5 ha to 2.38×10^5 ha in northern Laos. The increased swidden cultivation area was mainly distributed in Luang Prabang and southern B
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2019QZKK0206)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA20100300)+2 种基金the Youth Innovation Promotion Association CAS (2021073)the National Key Scientific and Technological Infrastructure project “Earth System Science Numerical Simulator Facility ” (EarthLab), the Natural Science Foundation of Hunan Province (Grant No. 2020JJ4074)the Open Fund Project of Key Lab of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education (2021VGE04)
文摘Terrestrial ecosystem water use efficiency(WUE)is an important indicator for coupling plant photosynthesis and transpiration,and is also a key factor linking the carbon and water cycles between the land and atmosphere.However,under the combination of climate change and human intervention,the change in WUE is still unclear,especially on the Tibetan Plateau(TP).Therefore,satellite remote sensing data and process-based terrestrial biosphere models(TBMs)are used in this study to investigate the spatiotemporal variations of WUE over the TP from 2001 to 2010.Then,the effects of land use and land cover change(LULCC)and CO_(2) fertilization on WUE from 1981-2010 are assessed using TBMs.Results show that climate change is the leading contributor to the change in WUE on the TP,and temperature is the most important factor.LULCC makes a negative contribution to WUE(-20.63%),which is greater than the positive contribution of CO_(2) fertilization(11.65%).In addition,CO_(2) fertilization can effectively improve ecosystem resilience on the TP.On the northwest plateau,the effects of LULCC and CO_(2) fertilization on WUE are more pronounced during the driest years than the annual average.These findings can help researchers understand the response of WUE to climate change and human activity and the coupling of the carbon and water cycles over the TP.
文摘The IPCC SRES narratives were implemented in IMAGE 2.2 to evaluate thefuture condition of the climate system (including the biosphere). A series of scenario experiments was used to assess possible ranges in emissions and concentrations of greenhouse gases, climate change and impacts. These experiments focussed on the role of the terrestrial carbon cycle. The experiments show that the SRES narratives dominate human emissions and not natural processes. In contrary, atmospheric CO2 concentration strongly differs between the experiments. Atmospheric CO2 concentrations range for A1B from 714 to 1009 ppmv CO2 in 2100. The spread of this range is comparable with the full SRES range as implemented in IMAGE 2.2 (515-895 μmol/mol CO2). The most important negative and positive feedback processes in IMAGE 2.2 on the build-up of CO2 concentrations are CO2 fertilisation and soil respiration respectively. Indirect effects of these processes furtherchange land-use patterns, deforestation rates and alter the natural C fluxes. The cumulative effects of these changes have a pronounced influence on the final CO2 concentrations. Our scenario experiments highlight the importance of a proper parameterisation of feedback processes, C-cycle and land use in determining the future states of the climate system.
基金the BMZ/GIZ “Green Rubber” (Project No. Project No. 13.1432.7-001.00)the CGIAR (Consultative Group for International Agricultural Research) Research Program 6: Forests, Trees and Agroforestry+2 种基金financially supported by the Federal Ministry for Economic Cooperation and Development, Germanyfunded by the National Natural Science Foundation of China (Grant No. 31450110067) the Chinese Academy of Science funded the Chinese Academy of Science funded the post-doc fellowship for Stefanie Goldberg (Grant No. 2013Y2SB0007)
文摘Soil respiration is a key component of the global carbon cycle, and even small changes in soil respiration rates could result in significant changes in atmospheric CO_2 levels. The conversion of tropical forests to rubber plantations in SE Asia is increasingly common, and there is a need to understand the impacts of this land-use change on soil respiration in order to revise CO_2 budget calculations. This study focused on the spatial variability of soil respiration along a slope in a natural tropical rainforest and a terraced rubber plantation in Xishuangbanna, Southwest(SW) China. In each land-use type, we inserted 105 collars for soil respiration measurements.Research was conducted over one year in Xishuangbanna during May, June, July and October 2015(wet season) and January and March 2016(dry season). The mean annual soil respiration rate was 30% higher in natural forest than in rubber plantation and mean fluxes in the wet and dry season were 15.1 and 9.5 Mg C ha^(-1) yr^(-1) in natural forest and 11.7 and 5.7 Mg C ha^(-1) yr^(-1) in rubber plantation. Using a linear mixedeffects model to assess the effect of changes in soil temperature and moisture on soil respiration, we found that soil temperature was the main driver of variation in soil respiration, explaining 48% of its seasonal variation in rubber plantation and 30% in natural forest. After including soil moisture, the model explained 70% of the variation in soil respiration in natural forest and 76% in rubber plantation. In the natural forest slope position had a significant effect on soil respiration, and soil temperature and soil moisture gradients only partly explained this correlation. In contrast, soil respiration in rubber plantation was not affected by slope position, which may be due to the terrace structure that resulted in more homogeneous environmental conditions along the slope. Further research is needed to determine whether or not these findings hold true at a landscape level.
基金the National Natural Science Foundation of China(No.31971497)by“Young Scholar"funding from Yunnan Province.
文摘Microbial carbon use efficiency(CUE)affects the soil C cycle to a great extent,but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood.In the current study,microcosms were used to investigate how microbial respiration,biomass,and CUE responded to biotic and abiotic factors in natural tropical,subtropical,and temperate forests.Soil samples from the forests were collected,sterilized,and populated with one or a combination of three types of soil organisms(the fungus Botrytis cinerea,the bacterium Escherichia coli,and the nematode Caenorhabditis elegans).The microcosms were then kept at the mean soil temperatures of the corresponding forests.Microbial respiration,biomass,and CUE were measured over one-month incubation period.The results showed that microbial biomass and CUE were significantly higher,but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil.Biotic factors mainly affected CUE by their effect on microbial biomass,while temperature affected CUE by altering respiration.Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass,respiration,and CUE,which would provide a basis for understanding the soil C cycle in forest ecosystems.
文摘1 Background THE C<sub>i</sub>/C<sub>a</sub>, the ratio of intercellular and ambient C0<sub>2</sub> partial pressure, is internally controlled by thestomatal conductance and assimilation rate, and is externally affected by the atmospheric CO<sub>2</sub> concentration and climate changes. C<sub>i</sub>/C<sub>a</sub> can be only estimated by the isotopic fractionation equation of Farquchar. However, this method is limited by the very little observation of atmospheric δ<sup>13</sup> C before1980. Leavitt had to interpolate the atmospheric δ<sup>13</sup> C by means of the polynomial. A geochemicalmethod to model C<sub>i</sub>/C<sub>a</sub> by tree-ring δ<sup>13</sup>C has been developed to reduce the dependence. By the estimated tree-ring C<sub>i</sub>/ C<sub>a</sub>, the authors here discuss C0<sub>2</sub> and water exchanges between the atmosphere and biosphere that greatly influence the climate
基金supported by the National Science Fund for Distinguished Young Scholars(41925001)National Youth Top-notch Talent Support Program(2015-48)+2 种基金Changjiang Young Scholars Programme of China(Q2016161)Fundamental Research Funds for the Central Universities(19lgjc02)the National Natural Science Foundation of China(41971018 and 31930072).
文摘It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn.However,this study challenges this consensus by comparing photosynthetic capability of terrestrial vegetation between the spring and autumn seasons based on measurements of 100 in situ eddy covariance towers over global extratropical ecosystems.At the majority of these sites,photosynthetic capability,indicated by light use efficiency(LUE)and apparent quantum efficiency,is significantly higher in autumn than in spring,due to lower atmosphere vapor pressure deficit(VPD)at the same air temperature.Seasonal VPD differences also substantially explain the interannual variability of the differences in photosynthetic capability between spring and autumn.We further reveal that VPD in autumn is significantly lower than in spring over 74.14% of extratropical areas,based on a global climate dataset.In contrast,LUE derived from a data-driven vegetation production dataset is significantly higher in autumn in over 61.02% of extratropical vegetated areas.Six Earth system models consistently projected continuous larger VPD values in spring compared with autumn,which implies that the impacts on vegetation growth will long exist and should be adequately considered when assessing the seasonal responses of terrestrial ecosystems to future climate conditions.
基金financial assistance and support from the Hubei Key Laboratory of Construction and Management in Hydropower Engineering,China Three Gorges University(No.2020KSD09)the National Key Research and Development Program of China(2017YFC0504102)+1 种基金the National Natural Science Foundation of China(51979147)the Ministry of Finance,the Ministry of Industry and Information Technology,and the Ministry of Science and Technology for support of the High Tech Zone in Yichang in creating a special project for highly talented research(No.B19-004)。
文摘Environmental changes significantly alter the structure,diversity and activity of soil microbial communities during spring freezing-thawing period,leading to changes in the soil microbial nitrogen cycle.Changes in N_(2)O fluxes after land use conversion from primary forest to secondary forest,Korean pine plantation and cropland in northeast China have not been quantified.Field experiments were conducted to measure soil N_(2)O fluxes in a primary forest,two secondary forests,a Korean pine plantation,and one maize field in a temperate region in northeast China from 2017-03-06 to 2017-05-28.During the experimental period,the soil was exclusively a nitrogen source for all land uses.We found that N_(2)O emissions ranged from 15.63 to 68.74μg m^(-2) h^(-1),and cumulative N_(2)O emissions ranged from 0.33 to 2.10 kg ha^(-1) during the period.Cumulative N_(2)O emissions from the maize field were significantly higher than that from primary forest,Korean pine plantation,hardwood forest,and Betula platyphylla forest by 262.1% to 536.4%.Compared with other ecosystems in similar studies,the N_(2)O emission rates of all ecosystem types in this study were low during the spring thaw period.Stepwise multiple linear regression indicated that there were significant correlations between N_(2)O emissions and environmental factors(air temperature and soil temperature,soil water content,soil p H,NH_(4)^(+)-N,NO_(3)^(-)-N,and soil organic carbon).The results showed that conversion of land use from primary forest to hardwood forest,Korean pine plantation or maize field greatly increased soil N_(2)O emissions during spring freezing-thawing period,and N_(2)O emissions from primary forest were almost the same as those from Betula platyphylla forest.
