The forest ecosystem plays an important role in the global carbon cycling. A study was conducted to evaluate soil CO2 flux and its seasonal and diurnal variation with the air and soil temperatures by using static clos...The forest ecosystem plays an important role in the global carbon cycling. A study was conducted to evaluate soil CO2 flux and its seasonal and diurnal variation with the air and soil temperatures by using static closed chamber technique in a typical broad-leaved/Korean pine mixed forest area on the northern slope of Changbai Mountain, Jilin Province, China. The experiment was carried out through the day and night in the growing season (from June to September) in situ and sample gas was analyzed by a gas chromatograph. Results showed that the forest floor was a large net source of carbon, and soil CO2 fluxes had an obvi-ous law of seasonal and diel variation. The soil CO2 flux of broad-leaved/Korean pine mixed forest was in the range of 0.302.42 mmol穖-2穝-1 with the mean value of 0.98 mmol穖-2穝-1. An examination on the seasonal pattern of soil CO2 emission suggested that the variability in soil CO2 flux could be correlated with variations in soil temperature, and the maximum of mean CO2 flux occurred in July ((1.27±23%) mmol穖-2穝-1) and the minimum was in September ((0.50±28%) mmol穖-2穝-1). The fluctuations in diel soil CO2 flux were also correlated with changes in soil temperature; however, there existed a factor for a time lag. Soil CO2 flux from the forest floor was strongly related to soil temperature and had the highest correlation with temperature at 6-cm depth of soil. Q10 values based on air temperature and soil temperature of different soil depths were at the ranges of 2.09–3.40.展开更多
Safe and economical disposal of paper mill sludge is a key consideration for forest products industry. A study was conducted to examine the effects of amendments of sludge and nutrients on soil surface CO2 flux （Rs）...Safe and economical disposal of paper mill sludge is a key consideration for forest products industry. A study was conducted to examine the effects of amendments of sludge and nutrients on soil surface CO2 flux （Rs） in northern hardwood forests and to quantify the relationship among Rs, soil temperature, and moisture in these stands. The experiment was a randomized complete block design that included sludge-amended, fertilized, and control treatments in sugar maple （Acer saccharum Marsh） dominated hardwood forests in the Upper Peninsula of Michigan, USA. Results showed that Rs was positively correlated to soil temperature （R^2 = 0.80, p 〈 0.001）, but was poorly correlated to soil moisture. Soil moisture positively affected the Rs only in the sludge-amended treatment. The Rs was significantly greater in the sludge-amended treatment than in the fertilized （p = 0.033） and the control （p = 0.048） treatments. The maximum Rs in the sludge-amended treatment was 8.8 μmol CO2 · m^ 2. s^-1, 91% and 126% greater than those in the fertilized （4.6 μmol CO2 · m^-2· s^-1） and control （3.9 μmol CO2· m^- 2· s^-1） treatments, respectively. The Rs did not differ significantly between the fertilized and control treatments. The difference in Rs between sludge-amended and the other treatments decreased with time following treatment.展开更多
As an important component of ecosystem carbon（C） budgets, soil carbon dioxide（CO2） flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiot...As an important component of ecosystem carbon（C） budgets, soil carbon dioxide（CO2） flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO2 flux（R（total））, its relative importance has never been systematically assessed. In this study, after comparative measurements of CO2 fluxes on sterilized and natural soils, the R（total） was partitioned into biotic flux（R（biotic）） and abiotic flux（R（abiotic）） across a broad range of land-cover types（including eight sampling sites： cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland） in Gurbantunggut Desert, Xinjiang, China. The relative contribution of R（abiotic） to R（total）, as well as the temperature dependency and predominant factors for R（total）, R（biotic） and R（abiotic）, were analyzed. Results showed that R（abiotic） always contributed to R（total） for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of R（abiotic） to R（total） was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R（abiotic） to R（total） logarithmically increased with decreasing R（biotic）, suggesting that R（abiotic） strongly affected R（total） when R（biotic） was low. This pattern confirms that soil CO2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R（abiotic） cannot result in net gain or net loss of CO2, but its effect on transient CO2 flux was significant. Temperature dependency of R（total） varied among the eight sampling sites and was determined by the predominant processes（abiotic or biotic） of CO2 flux. Specifically, R（biotic） was driven by soil temperature while R（abiotic） was regulated by the change in soil temperature（ΔT）. Namely, declining temperature（ΔT0） resulted in positive R（abiotic）（i.e., CO2 released from soil）. Without recognition of R（abiotic）, R（biotic） would be overestimated for the daytime and underestimated for the nighttime. Although R（abiotic） may not change the sum or the net value of daily soil CO2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R（total） exists widely in soils has widespread consequences for the understanding of C cycling.展开更多
Soil CO 2 emission from an arable soil was measured by closed chamber method to quantify year round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil...Soil CO 2 emission from an arable soil was measured by closed chamber method to quantify year round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil moisture content. Soil CO 2 flux, soil temperature, DOC and soil moisture content were determined on selected days during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil, the Chinese Academy of Sciences, in a subtropical region of China. Soil CO 2 fluxes were generally higher in summer and autumn than in winter and spring, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The estimation was 2 23 kgCO 2/(m 2·a) for average annual soil CO 2 flux. Regressed separately, the reasons for soil flux variability were 86 6% from soil temperature, 58 8% from DOC, and 26 3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained approximately 85 2% of the flux variance, however by stepwise regression, soil temperature was the dominant affecting soil flux. Based on the exponential equation developed from soil temperature, the predicted annual flux was 2 49 kgCO 2/(m 2·a), and essentially equal to the measured one. It is suggested the exponential relationship between soil flux and soil temperature could be used for accurately predicting soil CO 2 flux from arable soil in subtropical regions of China.展开更多
The United States continues to be the largest corn producer in the world. How to maximize corn yield and at the same time reduce greenhouse gas emissions, is becoming a challenging effort for growers and researchers. ...The United States continues to be the largest corn producer in the world. How to maximize corn yield and at the same time reduce greenhouse gas emissions, is becoming a challenging effort for growers and researchers. As a result, our understanding of the responses of soil CO2 and CH4 fluxes to agricultural practices in cornfields is still limited. We conducted a 3-yr cornfield experiment to study the responses of soil CO2 and CH4 fluxes to various agricultural practices in middle Tennessee. The agricultural practices included no-tillage + regular applications of urea ammonium nitrate (NT-URAN);no-tillage + regular applications of URAN + denitrification inhibitor (NT-inhi- bitor);no-tillage + regular applications of URAN + biochar (NT-biochar);no-tillage + 20% applications of URAN + chicken litter (NT-litter);no-tillage + split applications of URAN (NT-split);and conventional tillage + regular applications of URAN as a control (CT-URAN). A randomized complete block design was used with six replications. The same amount of fertilizer equivalent to 217 kg·N·ha-1 was applied to all of the experimental plots. The results showed that improved fertilizer and soil management, except the NT-biochar treatment significantly increased soil CO2 flux as compared to the conventional tillage (CT-URAN, 487.05 mg CO2 m-2·h-1). Soil CO2 flux increased exponentially with soil temperature (T 2 flux tended to be positively related to corn yield and/or soil moisture. Soil CH4 flux increased linearly with soil moisture in all treatments. Improved fertilizer and soil management did not alter soil CH4 flux, but significantly affected its moisture sensitivity. Our results indicated that agricultural practices enhancing corn yield may also result in a net increase in carbon emissions from soil, hence reducing the potential of carbon sequestration in croplands.展开更多
We investigated the effects of land-use changes on soil carbon storage and soil CO2 flux by comparing soils from mature cloud forest and 31-year-old secondary forest, both in the Santa Elena Forest Reserve, a municipa...We investigated the effects of land-use changes on soil carbon storage and soil CO2 flux by comparing soils from mature cloud forest and 31-year-old secondary forest, both in the Santa Elena Forest Reserve, a municipallyowned reserve at an elevation of 1600 to 1700 m near the town of Monteverde, and a clear-cut pasture near the reserve. Soils in the mature forest exhibit only weak horizonation but typically thick A horizons;they also consistently yield the highest carbon contents in the upper 30 cm. Soil CO2 flux was the highest in these soils, but also displayed the highest spatial variability. Secondary forest soils contain substantially less soil carbon than mature forest soils, but more than pasture soils. CO2 flux in the secondary forest soils was more similar to that of the mature forest, but displayed lower spatial variability. The pasture soils contain less soil carbon and produced lower CO2 flux levels than either of the forest soils. The pasture soils typically contain a well-defined coarse sandy layer 10 to 20 cm below the surface that we interpret as a sediment layer deposited across much of the landscape following a widespread erosion event, likely a consequence of the clear-cutting. Soil nitrogen concentrations are more than an order of magnitude lower than soil carbon concentrations, and display no trends between the different landscapes examined. Our preliminary results suggest that reforestation does restore soil carbon to clear-cut landscapes, but returning soil carbon levels to pre-land use levels occurs at a time scale of centuries, rather than decades.展开更多
高寒灌丛草甸和草甸均是青藏高原广泛分布的植被类型,在生态系统碳通量和区域碳循环中具有极其重要的作用。然而迄今为止,对其碳通量动态的时空变异还缺乏比较分析,对碳通量的季节和年际变异的主导影响因子认识还不够清晰,不利于深入理...高寒灌丛草甸和草甸均是青藏高原广泛分布的植被类型,在生态系统碳通量和区域碳循环中具有极其重要的作用。然而迄今为止,对其碳通量动态的时空变异还缺乏比较分析,对碳通量的季节和年际变异的主导影响因子认识还不够清晰,不利于深入理解生态系统碳通量格局及其形成机制。该研究选取位于青藏高原东部海北站高寒灌丛草甸和高原腹地当雄站高寒草原化草甸年降水量相近的5年(2004–2008年)的涡度相关CO_2通量连续观测数据,对生态系统净初级生产力(NEP)及其组分,包括总初级生产力(GPP)和生态系统呼吸的季节、年际动态及其影响因子进行了对比分析。结果表明:灌丛草甸的CO_2通量无论是季节还是年际累积量均高于草原化草甸,并且连续5年表现为"碳汇",平均每年NEP为70 g C·m^(–2)·a^(–1),高寒草原化草甸平均每年NEP为–5 g C·m^(–2)·a^(–1),几乎处于碳平衡状态,但其源/汇动态极不稳定,在2006年–88 g C·m^(–2)·a^(–1)的"碳源"至2008年54 g C·m^(–2)·a^(–1)的"碳汇"之间转换,具有较大的变异性。这两种高寒生态系统源/汇动态的差异主要源于归一化植被指数(NDVI)的差异,因为NDVI无论在年际水平还是季节水平都是NEP最直接的影响因子;其次,灌丛草甸还具有较高的碳利用效率(CUE,CUE=NEP/GPP),而年降水量和NDVI是决定两生态系统CUE大小的关键因子。两地区除了CO_2通量大小的差异外,其环境影响因子也有所不同。采用结构方程模型进行的通径分析表明,灌丛草甸生长季节CO_2通量的主要限制因子是温度,NEP和GPP主要受气温控制,随着气温升高而增加;而草原化草甸的CO_2通量多以季节性干旱导致的水分限制为主,其次才是气温的影响,受二者的共同限制。此外,两生态系统生长季节生态系统呼吸主要受GPP和5 cm土壤温度的直接影响,其中GPP起主导作用,非生长季节生态系统呼吸主要受5 cm土壤温度影响。该研究还表明,水热因子的协调度是决定青藏高原高寒草地GPP和NEP的关键要素。展开更多
Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was ...Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was used to investigate the differences in soil carbon dioxide （CO2） emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems （P〉0.05）. However, significant differences in CO2 emissions from soils were observed among the three cropping systems （P〈0.05）. Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order： continuous maize （（829±10） g CO2 m2）〉continuous wheat （（629±22） g CO2 m^2）〉continuous soybean （（474±30） g CO2 m-2）. Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature （T, ~C） and water-filled pore space （W, %）, log（]）=a＋bT log（W）, was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.展开更多
Understanding the effects of warming on greenhouse gas（GHG, such as N2O, CH4 and CO2 ）feedbacks to climate change represents the major environmental issue. However, little information is available on how warming eff...Understanding the effects of warming on greenhouse gas（GHG, such as N2O, CH4 and CO2 ）feedbacks to climate change represents the major environmental issue. However, little information is available on how warming effects on GHG fluxes in farmland of North China Plain（NCP）. An infrared warming simulation experiment was used to assess the responses of N2O, CH4 and CO2 to warming in wheat season of 2012–2014 from conventional tillage（CT） and no-tillage（NT） systems. The results showed that warming increased cumulative N2O emission by 7.7% in CT but decreased it by 9.7% in NT fields（p 〈 0.05）. Cumulative CH4 uptake and CO2 emission were increased by 28.7%–51.7% and 6.3%–15.9% in both two tillage systems,respectively（p 〈 0.05）. The stepwise regressions relationship between GHG fluxes and soil temperature and soil moisture indicated that the supply soil moisture due to irrigation and precipitation would enhance the positive warming effects on GHG fluxes in two wheat seasons.However, in 2013, the long-term drought stress due to infrared warming and less precipitation decreased N2O and CO2 emission in warmed treatments. In contrast, warming during this time increased CH4 emission from deep soil depth. Across two years wheat seasons, warming significantly decreased by 30.3% and 63.9% sustained-flux global warming potential（SGWP） of N2O and CH4 expressed as CO2 equivalent in CT and NT fields, respectively. However, increase in soil CO2 emission indicated that future warming projection might provide positive feedback between soil C release and global warming in NCP.展开更多
Global food demand requires that soils be used intensively for agriculture, but how these soils are managed greatly impacts soil fluxes of carbon dioxide (CO2). Soil management practices can cause carbon to be either ...Global food demand requires that soils be used intensively for agriculture, but how these soils are managed greatly impacts soil fluxes of carbon dioxide (CO2). Soil management practices can cause carbon to be either sequestered or emitted, with corresponding uncertain influence on atmospheric CO2 concentrations. The situation is further complicated by the lack of CO2 flux measurements for African subsistence farms. For widespread application in remote areas, a simple experimental methodology is desired. As a first step, the present study investigated the use of Bowen Ratio Energy Balance (BREB) instrumentation to measure the energy balance and CO2 fluxes of two contrasting crop management systems, till and no-till, in the lowlands within the mountains of Lesotho. Two BREB micrometeorological systems were established on 100-m by 100-m sites, both planted with maize (Zea mays) but under either conventional (plow, disk-disk) or no-till soil mangement systems. The results demonstrate that with careful maintenance of the instruments by appropriately trained local personnel, the BREB approach offers substantial benefits in measuring real time changes in agroecosystem CO2 flux. The periods where the two treatments could be compared indicated greater CO2 sequestration over the no-till treatments during both the growing and non-growing seasons.展开更多
基金This research was supported by National Natural Science Foundation of China (Grant No. 40171092).
文摘The forest ecosystem plays an important role in the global carbon cycling. A study was conducted to evaluate soil CO2 flux and its seasonal and diurnal variation with the air and soil temperatures by using static closed chamber technique in a typical broad-leaved/Korean pine mixed forest area on the northern slope of Changbai Mountain, Jilin Province, China. The experiment was carried out through the day and night in the growing season (from June to September) in situ and sample gas was analyzed by a gas chromatograph. Results showed that the forest floor was a large net source of carbon, and soil CO2 fluxes had an obvi-ous law of seasonal and diel variation. The soil CO2 flux of broad-leaved/Korean pine mixed forest was in the range of 0.302.42 mmol穖-2穝-1 with the mean value of 0.98 mmol穖-2穝-1. An examination on the seasonal pattern of soil CO2 emission suggested that the variability in soil CO2 flux could be correlated with variations in soil temperature, and the maximum of mean CO2 flux occurred in July ((1.27±23%) mmol穖-2穝-1) and the minimum was in September ((0.50±28%) mmol穖-2穝-1). The fluctuations in diel soil CO2 flux were also correlated with changes in soil temperature; however, there existed a factor for a time lag. Soil CO2 flux from the forest floor was strongly related to soil temperature and had the highest correlation with temperature at 6-cm depth of soil. Q10 values based on air temperature and soil temperature of different soil depths were at the ranges of 2.09–3.40.
基金The research was funded by a NCASI grant to S.T. Gower. Wang CK was supported by Innovated Talent Program of Northeast Forestry University (2004-07)
文摘Safe and economical disposal of paper mill sludge is a key consideration for forest products industry. A study was conducted to examine the effects of amendments of sludge and nutrients on soil surface CO2 flux （Rs） in northern hardwood forests and to quantify the relationship among Rs, soil temperature, and moisture in these stands. The experiment was a randomized complete block design that included sludge-amended, fertilized, and control treatments in sugar maple （Acer saccharum Marsh） dominated hardwood forests in the Upper Peninsula of Michigan, USA. Results showed that Rs was positively correlated to soil temperature （R^2 = 0.80, p 〈 0.001）, but was poorly correlated to soil moisture. Soil moisture positively affected the Rs only in the sludge-amended treatment. The Rs was significantly greater in the sludge-amended treatment than in the fertilized （p = 0.033） and the control （p = 0.048） treatments. The maximum Rs in the sludge-amended treatment was 8.8 μmol CO2 · m^ 2. s^-1, 91% and 126% greater than those in the fertilized （4.6 μmol CO2 · m^-2· s^-1） and control （3.9 μmol CO2· m^- 2· s^-1） treatments, respectively. The Rs did not differ significantly between the fertilized and control treatments. The difference in Rs between sludge-amended and the other treatments decreased with time following treatment.
基金supported by the National Natural Science Foundation of China (41301279, 41201041)the International Science & Technology Cooperation Program of China (2010DFA92720)the Knowledge Innovation Project of the Chinese Academy of Sciences (KZCX2-YW-T09)
文摘As an important component of ecosystem carbon（C） budgets, soil carbon dioxide（CO2） flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO2 flux（R（total））, its relative importance has never been systematically assessed. In this study, after comparative measurements of CO2 fluxes on sterilized and natural soils, the R（total） was partitioned into biotic flux（R（biotic）） and abiotic flux（R（abiotic）） across a broad range of land-cover types（including eight sampling sites： cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland） in Gurbantunggut Desert, Xinjiang, China. The relative contribution of R（abiotic） to R（total）, as well as the temperature dependency and predominant factors for R（total）, R（biotic） and R（abiotic）, were analyzed. Results showed that R（abiotic） always contributed to R（total） for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of R（abiotic） to R（total） was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R（abiotic） to R（total） logarithmically increased with decreasing R（biotic）, suggesting that R（abiotic） strongly affected R（total） when R（biotic） was low. This pattern confirms that soil CO2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R（abiotic） cannot result in net gain or net loss of CO2, but its effect on transient CO2 flux was significant. Temperature dependency of R（total） varied among the eight sampling sites and was determined by the predominant processes（abiotic or biotic） of CO2 flux. Specifically, R（biotic） was driven by soil temperature while R（abiotic） was regulated by the change in soil temperature（ΔT）. Namely, declining temperature（ΔT0） resulted in positive R（abiotic）（i.e., CO2 released from soil）. Without recognition of R（abiotic）, R（biotic） would be overestimated for the daytime and underestimated for the nighttime. Although R（abiotic） may not change the sum or the net value of daily soil CO2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R（total） exists widely in soils has widespread consequences for the understanding of C cycling.
文摘Soil CO 2 emission from an arable soil was measured by closed chamber method to quantify year round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil moisture content. Soil CO 2 flux, soil temperature, DOC and soil moisture content were determined on selected days during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil, the Chinese Academy of Sciences, in a subtropical region of China. Soil CO 2 fluxes were generally higher in summer and autumn than in winter and spring, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The estimation was 2 23 kgCO 2/(m 2·a) for average annual soil CO 2 flux. Regressed separately, the reasons for soil flux variability were 86 6% from soil temperature, 58 8% from DOC, and 26 3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained approximately 85 2% of the flux variance, however by stepwise regression, soil temperature was the dominant affecting soil flux. Based on the exponential equation developed from soil temperature, the predicted annual flux was 2 49 kgCO 2/(m 2·a), and essentially equal to the measured one. It is suggested the exponential relationship between soil flux and soil temperature could be used for accurately predicting soil CO 2 flux from arable soil in subtropical regions of China.
文摘The United States continues to be the largest corn producer in the world. How to maximize corn yield and at the same time reduce greenhouse gas emissions, is becoming a challenging effort for growers and researchers. As a result, our understanding of the responses of soil CO2 and CH4 fluxes to agricultural practices in cornfields is still limited. We conducted a 3-yr cornfield experiment to study the responses of soil CO2 and CH4 fluxes to various agricultural practices in middle Tennessee. The agricultural practices included no-tillage + regular applications of urea ammonium nitrate (NT-URAN);no-tillage + regular applications of URAN + denitrification inhibitor (NT-inhi- bitor);no-tillage + regular applications of URAN + biochar (NT-biochar);no-tillage + 20% applications of URAN + chicken litter (NT-litter);no-tillage + split applications of URAN (NT-split);and conventional tillage + regular applications of URAN as a control (CT-URAN). A randomized complete block design was used with six replications. The same amount of fertilizer equivalent to 217 kg·N·ha-1 was applied to all of the experimental plots. The results showed that improved fertilizer and soil management, except the NT-biochar treatment significantly increased soil CO2 flux as compared to the conventional tillage (CT-URAN, 487.05 mg CO2 m-2·h-1). Soil CO2 flux increased exponentially with soil temperature (T 2 flux tended to be positively related to corn yield and/or soil moisture. Soil CH4 flux increased linearly with soil moisture in all treatments. Improved fertilizer and soil management did not alter soil CH4 flux, but significantly affected its moisture sensitivity. Our results indicated that agricultural practices enhancing corn yield may also result in a net increase in carbon emissions from soil, hence reducing the potential of carbon sequestration in croplands.
文摘We investigated the effects of land-use changes on soil carbon storage and soil CO2 flux by comparing soils from mature cloud forest and 31-year-old secondary forest, both in the Santa Elena Forest Reserve, a municipallyowned reserve at an elevation of 1600 to 1700 m near the town of Monteverde, and a clear-cut pasture near the reserve. Soils in the mature forest exhibit only weak horizonation but typically thick A horizons;they also consistently yield the highest carbon contents in the upper 30 cm. Soil CO2 flux was the highest in these soils, but also displayed the highest spatial variability. Secondary forest soils contain substantially less soil carbon than mature forest soils, but more than pasture soils. CO2 flux in the secondary forest soils was more similar to that of the mature forest, but displayed lower spatial variability. The pasture soils contain less soil carbon and produced lower CO2 flux levels than either of the forest soils. The pasture soils typically contain a well-defined coarse sandy layer 10 to 20 cm below the surface that we interpret as a sediment layer deposited across much of the landscape following a widespread erosion event, likely a consequence of the clear-cutting. Soil nitrogen concentrations are more than an order of magnitude lower than soil carbon concentrations, and display no trends between the different landscapes examined. Our preliminary results suggest that reforestation does restore soil carbon to clear-cut landscapes, but returning soil carbon levels to pre-land use levels occurs at a time scale of centuries, rather than decades.
文摘高寒灌丛草甸和草甸均是青藏高原广泛分布的植被类型,在生态系统碳通量和区域碳循环中具有极其重要的作用。然而迄今为止,对其碳通量动态的时空变异还缺乏比较分析,对碳通量的季节和年际变异的主导影响因子认识还不够清晰,不利于深入理解生态系统碳通量格局及其形成机制。该研究选取位于青藏高原东部海北站高寒灌丛草甸和高原腹地当雄站高寒草原化草甸年降水量相近的5年(2004–2008年)的涡度相关CO_2通量连续观测数据,对生态系统净初级生产力(NEP)及其组分,包括总初级生产力(GPP)和生态系统呼吸的季节、年际动态及其影响因子进行了对比分析。结果表明:灌丛草甸的CO_2通量无论是季节还是年际累积量均高于草原化草甸,并且连续5年表现为"碳汇",平均每年NEP为70 g C·m^(–2)·a^(–1),高寒草原化草甸平均每年NEP为–5 g C·m^(–2)·a^(–1),几乎处于碳平衡状态,但其源/汇动态极不稳定,在2006年–88 g C·m^(–2)·a^(–1)的"碳源"至2008年54 g C·m^(–2)·a^(–1)的"碳汇"之间转换,具有较大的变异性。这两种高寒生态系统源/汇动态的差异主要源于归一化植被指数(NDVI)的差异,因为NDVI无论在年际水平还是季节水平都是NEP最直接的影响因子;其次,灌丛草甸还具有较高的碳利用效率(CUE,CUE=NEP/GPP),而年降水量和NDVI是决定两生态系统CUE大小的关键因子。两地区除了CO_2通量大小的差异外,其环境影响因子也有所不同。采用结构方程模型进行的通径分析表明,灌丛草甸生长季节CO_2通量的主要限制因子是温度,NEP和GPP主要受气温控制,随着气温升高而增加;而草原化草甸的CO_2通量多以季节性干旱导致的水分限制为主,其次才是气温的影响,受二者的共同限制。此外,两生态系统生长季节生态系统呼吸主要受GPP和5 cm土壤温度的直接影响,其中GPP起主导作用,非生长季节生态系统呼吸主要受5 cm土壤温度影响。该研究还表明,水热因子的协调度是决定青藏高原高寒草地GPP和NEP的关键要素。
基金supported by the Key Research Program of the Chinese Academy of Sciences (KZZD-EW-TZ-16-02)the Foundation for Young Talents of the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences (DLSYQ13001)the National Natural Science Foundation of China (41101283)
文摘Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was used to investigate the differences in soil carbon dioxide （CO2） emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems （P〉0.05）. However, significant differences in CO2 emissions from soils were observed among the three cropping systems （P〈0.05）. Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order： continuous maize （（829±10） g CO2 m2）〉continuous wheat （（629±22） g CO2 m^2）〉continuous soybean （（474±30） g CO2 m-2）. Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature （T, ~C） and water-filled pore space （W, %）, log（]）=a＋bT log（W）, was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.
基金supported by the National Natural Science Foundation of China(No.31170414)the 100 Talents Program of Chinese Academy of Science(No.2009)
文摘Understanding the effects of warming on greenhouse gas（GHG, such as N2O, CH4 and CO2 ）feedbacks to climate change represents the major environmental issue. However, little information is available on how warming effects on GHG fluxes in farmland of North China Plain（NCP）. An infrared warming simulation experiment was used to assess the responses of N2O, CH4 and CO2 to warming in wheat season of 2012–2014 from conventional tillage（CT） and no-tillage（NT） systems. The results showed that warming increased cumulative N2O emission by 7.7% in CT but decreased it by 9.7% in NT fields（p 〈 0.05）. Cumulative CH4 uptake and CO2 emission were increased by 28.7%–51.7% and 6.3%–15.9% in both two tillage systems,respectively（p 〈 0.05）. The stepwise regressions relationship between GHG fluxes and soil temperature and soil moisture indicated that the supply soil moisture due to irrigation and precipitation would enhance the positive warming effects on GHG fluxes in two wheat seasons.However, in 2013, the long-term drought stress due to infrared warming and less precipitation decreased N2O and CO2 emission in warmed treatments. In contrast, warming during this time increased CH4 emission from deep soil depth. Across two years wheat seasons, warming significantly decreased by 30.3% and 63.9% sustained-flux global warming potential（SGWP） of N2O and CH4 expressed as CO2 equivalent in CT and NT fields, respectively. However, increase in soil CO2 emission indicated that future warming projection might provide positive feedback between soil C release and global warming in NCP.
文摘Global food demand requires that soils be used intensively for agriculture, but how these soils are managed greatly impacts soil fluxes of carbon dioxide (CO2). Soil management practices can cause carbon to be either sequestered or emitted, with corresponding uncertain influence on atmospheric CO2 concentrations. The situation is further complicated by the lack of CO2 flux measurements for African subsistence farms. For widespread application in remote areas, a simple experimental methodology is desired. As a first step, the present study investigated the use of Bowen Ratio Energy Balance (BREB) instrumentation to measure the energy balance and CO2 fluxes of two contrasting crop management systems, till and no-till, in the lowlands within the mountains of Lesotho. Two BREB micrometeorological systems were established on 100-m by 100-m sites, both planted with maize (Zea mays) but under either conventional (plow, disk-disk) or no-till soil mangement systems. The results demonstrate that with careful maintenance of the instruments by appropriately trained local personnel, the BREB approach offers substantial benefits in measuring real time changes in agroecosystem CO2 flux. The periods where the two treatments could be compared indicated greater CO2 sequestration over the no-till treatments during both the growing and non-growing seasons.
