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Marc Aubinet - One of the best experts on this subject based on the ideXlab platform.
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Rotational and continuous grazing does not affect the total Net Ecosystem Exchange of a pasture grazed by cattle but modifies CO2 Exchange dynamics
Agriculture Ecosystems & Environment, 2018Co-Authors: Louis Gourlez De La Motte, Ossénatou Mamadou, Yves Beckers, Bernard Bodson, Bernard Heinesch, Marc AubinetAbstract:Abstract Grassland carbon budgets are known to be greatly dependent on management. In particular, grazing is known to directly affect CO2 Exchange through consumption by plants, cattle respiration, natural fertilisation through excreta, and soil compaction. This study investigates the impact of two grazing methods on the Net Ecosystem Exchange (NEE) dynamics and carbon balance, by measuring CO2 fluxes using eddy covariance in two adjacent pastures located in southern Belgium during a complete grazing season. Rotational (RG) grazing consists of an alternation of rest periods and short high stock density grazing periods. Continuous grazing (CG) consists of uninterrupted grazing with variable stocking rates. To our knowledge, this is the first study to assess the impact of these grazing methods on total Net Ecosystem Exchange and CO2 Exchange dynamics using eddy covariance. The results showed that NEE dynamics were greatly impacted by the grazing method. Following grazing events on the RG parcel, Net CO2 uptake on the RG parcel was reduced compared to the CG parcel. During the following rest periods, this phenomenon progressively shifted towards a higher assimilation for the RG treatment. This behaviour was attributed to sharp biomass changes in the RG treatment and therefore sharp changes in plant photosynthetic capacity. We found that differences in gross primary productivity at high radiation were strongly correlated to differences in standing biomass. In terms of carbon budgets, no significant difference was observed between the two treatments, neither in cumulative NEE, or in terms of estimated biomass production. The results of our study suggest that we should not expect major benefits in terms of CO2 uptake from rotational grazing management when compared to continuous grazing management in intensively managed temperate pastures.
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Impact of CO2 storage flux sampling uncertainty on Net Ecosystem Exchange measured by eddy covariance
Agricultural and Forest Meteorology, 2018Co-Authors: Giacomo Nicolini, Marc Aubinet, Ossénatou Mamadou, Bernard Heinesch, Leonardo Montagnani, Christian Feigenwinter, Anders Lindroth, Uta Moderow, Meelis Mölder, Corinna RebmannAbstract:Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements quantify the Net Ecosystem Exchange (NEE) by summing the flux obtained by EC (FC) and the storage flux (SC). SC is the rate of change of a scalar, CO2 molar fraction in this case, within the control volume underneath the EC measurement level. It is given by the difference in the quasi-instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. The approaches used to estimate SC largely vary, from measurements based on a single sampling point usually located at the EC measurement height, to measurements based on profile sampling. Generally a single profile is used, although multiple profiles can be positioned within the control volume. Measurement accuracy reasonably increases with the spatial sampling intensity, however limited resources often prevent more elaborated measurement systems. In this study we use the experimental dataset collected during the ADVEX campaign in which turbulent and non-turbulent fluxes were measured in three forest sites by the simultaneous use of five towers/profiles. Our main objectives are to evaluate both the uncertainty of SC that derives from an insufficient sampling of CO2 variability, and its impact on concurrent NEE estimates.Results show that different measurement methods may produce substantially different SC flux estimates which in some cases involve a significant underestimation of the actual SC at a half-hourly time scales. A proper measuring system, that uses a single vertical profile of which the CO2 sampled at 3 points (the two closest to the ground and the one at the lower fringe of the canopy layer) is averaged with CO2 sampled at a certain distance and at the same height, improves the horizontal representativeness and reduces this (proportional) bias to 2–10% in such Ecosystems. While the effect of this error is minor on long term NEE estimates, it can produce significant uncertainty on half-hourly NEE fluxes.
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Thermal optimality of Net Ecosystem Exchange of carbon dioxide and underlying mechanisms.
The New Phytologist, 2012Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, David Schimel, Beverly E. Law, Almut Arneth, Wenping Yuan, Christof Ammann, Muhammad Asif Arain, Marc AubinetAbstract:• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of Ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of Net Ecosystem Exchange (NEE), an Ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of Ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed Ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within Ecosystems, and has the potential to significantly regulate Ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of Ecosystems in changing environments and benchmarking global models.
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Latitudinal patterns of magnitude and interannual variability in Net Ecosystem Exchange regulated by biological and environmental variables
Global Change Biology, 2009Co-Authors: Wenping Yuan, Yiqi Luo, Xuhui Zhou, Reinhart Ceulemans, Ram Oren, Ivan A. Janssens, Andrew D. Richardson, Sebastiaan Luyssaert, Thomas Grünwald, Marc AubinetAbstract:Over the last two and half decades, strong evidence showed that the terrestrial Ecosystems are acting as a Net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in Net Ecosystem Exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29°N to ~64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is Ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
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Discriminating Net Ecosystem Exchange between different vegetation plots in a heterogeneous forest
Agricultural and Forest Meteorology, 2005Co-Authors: Marc Aubinet, Bernard Heinesch, Dominique Perrin, Christine MoureauxAbstract:Abstract A model describing the half-hourly evolution of the Net Ecosystem Exchange of a heterogeneous forest was developed. It viewed the forest as a patchwork of three homogeneous vegetation plots whose contribution varied with wind direction. The model was calibrated on eight (1997–2004) years of measurements made at the Vielsalm experimental site in Belgium. The first 6 years were used for model calibration, the last two for validation. The model predicted the eddy flux measured by the system with a degree of performance comparable with those of other models running on the same time scale on homogeneous canopies. The model also allowed the three Ecosystem behaviours to be differentiated: the beech characterised by higher carbon sequestration efficiency during the growth period; but also by a shorter growth period, the Douglas fir and the spruce/silver fir characterised by a longer growth period, with the efficiency of the former higher than the latter. The evolution with wind direction of the beech forest contribution (i.e., the relative contribution of the beech plot to the total measured flux) was also obtained and was found to be in very good agreement with footprint predictions on average. However, on a half-hourly scale the agreement between observed and predicted beech forest contributions was not so good. In particular, it was found that the predictions made by footprint models of the variations due to longitudinal footprint changes were not observed by the experimental system.
Yiqi Luo - One of the best experts on this subject based on the ideXlab platform.
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Direct and indirect effects of climatic variations on the interannual variability in Net Ecosystem Exchange across terrestrial Ecosystems
Tellus B: Chemical and Physical Meteorology, 2016Co-Authors: Junjiong Shao, Yiqi Luo, Xuhui Zhou, Mika Aurela, David P. Billesbach, Peter D. Blanken, Rosvel Bracho, Jiquan Chen, Marc L. FischerAbstract:Climatic variables not only directly affect the interannual variability (IAV) in Net Ecosystem Exchange of CO 2 (NEE) but also indirectly drive it by changing the physiological parameters. Identifying these direct and indirect paths can reveal the underlying mechanisms of carbon (C) dynamics. In this study, we applied a path analysis using flux data from 65 sites to quantify the direct and indirect climatic effects on IAV in NEE and to evaluate the potential relationships among the climatic variables and physiological parameters that represent physiology and phenology of Ecosystems. We found that the maximum photosynthetic rate was the most important factor for the IAV in gross primary productivity (GPP), which was mainly induced by the variation in vapour pressure deficit. For Ecosystem respiration (RE), the most important drivers were GPP and the reference respiratory rate. The biome type regulated the direct and indirect paths, with distinctive differences between forests and non-forests, evergreen needleleaf forests and deciduous broadleaf forests, and between grasslands and croplands. Different paths were also found among wet, moist and dry Ecosystems. However, the climatic variables can only partly explain the IAV in physiological parameters, suggesting that the latter may also result from other biotic and disturbance factors. In addition, the climatic variables related to NEE were not necessarily the same as those related to GPP and RE, indicating the emerging difficulty encountered when studying the IAV in NEE. Overall, our results highlight the contribution of certain physiological parameters to the IAV in C fluxes and the importance of biome type and multi-year water conditions, which should receive more attention in future experimental and modelling research. Keywords: Net Ecosystem Exchange, interannual variability, climatic variations, physiological parameters, direct and indirect effects, relative importance (Published: 2 August 2016) Citation: Tellus B 2016, 68, 30575, http://dx.doi.org/10.3402/tellusb.v68.30575
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Differential Responses of Net Ecosystem Exchange of Carbon Dioxide to Light and Temperature between Spring and Neap Tides in Subtropical Mangrove Forests
TheScientificWorldJournal, 2014Co-Authors: Hui Chen, Yiqi Luo, Guanghui LinAbstract:The eddy flux data with field records of tidal water inundation depths of the year 2010 from two mangroves forests in southern China were analyzed to investigate the tidal effect on mangrove carbon cycle. We compared the Net Ecosystem Exchange (NEE) and its responses to light and temperature, respectively, between spring tide and neap tide inundation periods. For the most time of the year 2010, higher daytime NEE values were found during spring tides than during neap tides at both study sites. Regression analysis of daytime NEE to photosynthetically active radiation (PAR) using the Landsberg model showed increased sensitivity of NEE to PAR with higher maximum photosynthetic rate during spring tides than neap tides. In contrast, the light compensation points acquired from the regression function of the Landsberg model were smaller during spring tides than neap tides in most months. The dependence of nighttime NEE on soil temperature was lower under spring tide than under neap tides. All these results above indicated that Ecosystem carbon uptake rates of mangrove forests were strengthened, while Ecosystem respirations were inhibited during spring tides in comparison with those during neap tides, which needs to be considered in modeling mangrove Ecosystem carbon cycle under future sea level rise scenarios.
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Thermal optimality of Net Ecosystem Exchange of carbon dioxide and underlying mechanisms.
The New Phytologist, 2012Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, David Schimel, Beverly E. Law, Almut Arneth, Wenping Yuan, Christof Ammann, Muhammad Asif Arain, Marc AubinetAbstract:• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of Ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of Net Ecosystem Exchange (NEE), an Ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of Ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed Ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within Ecosystems, and has the potential to significantly regulate Ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of Ecosystems in changing environments and benchmarking global models.
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Seasonal hysteresis of Net Ecosystem Exchange in response to temperature change: patterns and causes
Global Change Biology, 2011Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, Leonardo Montagnani, Gil Bohrer, Ivan A. Janssens, Bert Gielen, Serge Rambal, Eddy Moors, Giorgio MatteucciAbstract:Understanding how Net Ecosystem Exchange (NEE) changes with temperature is central to the debate on climate change-carbon cycle feedbacks, but still remains unclear. Here, we used eddy covariance measurements of NEE from 20 FLUXNet sites (203 site-years of data) in mid- and high-latitude forests to investigate the temperature response of NEE. Years were divided into two half thermal years (increasing temperature in spring and decreasing temperature in autumn) using the maximum daily mean temperature. We observed a parabolic-like pattern of NEE in response to temperature change in both the spring and autumn half thermal years. However, at similar temperatures, NEE was considerably depressed during the decreasing temperature season as compared with the increasing temperature season, inducing a counter-clockwise hysteresis pattern in the NEE–temperature relation at most sites. The magnitude of this hysteresis was attributable mostly (68%) to gross primary production (GPP) differences but little (8%) to Ecosystem respiration (ER) differences between the two half thermal years. The main environmental factors contributing to the hysteresis responses of NEE and GPP were daily accumulated radiation. Soil water content (SWC) also contributed to the hysteresis response of GPP but only at some sites. Shorter day length, lower light intensity, lower SWC and reduced photosynthetic capacity may all have contributed to the depressed GPP and Net carbon uptake during the decreasing temperature seasons. The resultant hysteresis loop is an important indicator of the existence of limiting factors. As such, the role of radiation, LAI and SWC should be considered when modeling the dynamics of carbon cycling in response to temperature change.
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Thermal adaptation of Net Ecosystem Exchange
2011Co-Authors: Wenping Yuan, Shuli Niu, Yiqi Luo, S. Liang, P. Stoy, J. Chen, A. R. Desai, A. Lindroth, C. M. GoughAbstract:Abstract. Thermal adaptation of gross primary production and Ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of Net Ecosystem Exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland Ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (Tb) at which Ecosystem transferring from carbon source to sink and optimal temperature (To) at which carbon uptake is maximized. Tb was strongly correlated with annual mean air temperature. To was strongly correlated with mean temperature during the Net carbon uptake period across the study Ecosystems. Our results suggested that Ecosystem CO2 flux switched from source to sink when air temperature reached annual mean temperature in spring and reached maximum uptake at mean temperature of the Net carbon uptake period. Our results imply that the Net Ecosystem Exchange of carbon adapt to the temperature across the geographical range due to intrinsic connections between vegetation primary production and Ecosystem respiration.
Shuli Niu - One of the best experts on this subject based on the ideXlab platform.
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Thermal optimality of Net Ecosystem Exchange of carbon dioxide and underlying mechanisms.
The New Phytologist, 2012Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, David Schimel, Beverly E. Law, Almut Arneth, Wenping Yuan, Christof Ammann, Muhammad Asif Arain, Marc AubinetAbstract:• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of Ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of Net Ecosystem Exchange (NEE), an Ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of Ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed Ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within Ecosystems, and has the potential to significantly regulate Ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of Ecosystems in changing environments and benchmarking global models.
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Seasonal hysteresis of Net Ecosystem Exchange in response to temperature change: patterns and causes
Global Change Biology, 2011Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, Leonardo Montagnani, Gil Bohrer, Ivan A. Janssens, Bert Gielen, Serge Rambal, Eddy Moors, Giorgio MatteucciAbstract:Understanding how Net Ecosystem Exchange (NEE) changes with temperature is central to the debate on climate change-carbon cycle feedbacks, but still remains unclear. Here, we used eddy covariance measurements of NEE from 20 FLUXNet sites (203 site-years of data) in mid- and high-latitude forests to investigate the temperature response of NEE. Years were divided into two half thermal years (increasing temperature in spring and decreasing temperature in autumn) using the maximum daily mean temperature. We observed a parabolic-like pattern of NEE in response to temperature change in both the spring and autumn half thermal years. However, at similar temperatures, NEE was considerably depressed during the decreasing temperature season as compared with the increasing temperature season, inducing a counter-clockwise hysteresis pattern in the NEE–temperature relation at most sites. The magnitude of this hysteresis was attributable mostly (68%) to gross primary production (GPP) differences but little (8%) to Ecosystem respiration (ER) differences between the two half thermal years. The main environmental factors contributing to the hysteresis responses of NEE and GPP were daily accumulated radiation. Soil water content (SWC) also contributed to the hysteresis response of GPP but only at some sites. Shorter day length, lower light intensity, lower SWC and reduced photosynthetic capacity may all have contributed to the depressed GPP and Net carbon uptake during the decreasing temperature seasons. The resultant hysteresis loop is an important indicator of the existence of limiting factors. As such, the role of radiation, LAI and SWC should be considered when modeling the dynamics of carbon cycling in response to temperature change.
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Thermal adaptation of Net Ecosystem Exchange
2011Co-Authors: Wenping Yuan, Shuli Niu, Yiqi Luo, S. Liang, P. Stoy, J. Chen, A. R. Desai, A. Lindroth, C. M. GoughAbstract:Abstract. Thermal adaptation of gross primary production and Ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of Net Ecosystem Exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland Ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (Tb) at which Ecosystem transferring from carbon source to sink and optimal temperature (To) at which carbon uptake is maximized. Tb was strongly correlated with annual mean air temperature. To was strongly correlated with mean temperature during the Net carbon uptake period across the study Ecosystems. Our results suggested that Ecosystem CO2 flux switched from source to sink when air temperature reached annual mean temperature in spring and reached maximum uptake at mean temperature of the Net carbon uptake period. Our results imply that the Net Ecosystem Exchange of carbon adapt to the temperature across the geographical range due to intrinsic connections between vegetation primary production and Ecosystem respiration.
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Thermal adaptation of Net Ecosystem Exchange
Biogeosciences, 2011Co-Authors: Wenping Yuan, Shuli Niu, Yiqi Luo, S. Liang, P. Stoy, J. Chen, A. R. Desai, A. Lindroth, C. M. Gough, R. CeulemansAbstract:Thermal adaptation of gross primary production and Ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of Net Ecosystem Exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland Ecosystems located at latitudes ranging from similar to 29 degrees N to 64 degrees N. The response curves were used to define two critical temperatures: transition temperature (T(b)) at which Ecosystem transfer from carbon source to sink and optimal temperature (T(o)) at which carbon uptake is maximized. T(b) was strongly correlated with annual mean air temperature. T(o) was strongly correlated with mean temperature during the Net carbon uptake period across the study Ecosystems. Our results imply that the Net Ecosystem Exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and Ecosystem respiration.
Wenping Yuan - One of the best experts on this subject based on the ideXlab platform.
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Thermal optimality of Net Ecosystem Exchange of carbon dioxide and underlying mechanisms.
The New Phytologist, 2012Co-Authors: Shuli Niu, Yiqi Luo, Shenfeng Fei, David Schimel, Beverly E. Law, Almut Arneth, Wenping Yuan, Christof Ammann, Muhammad Asif Arain, Marc AubinetAbstract:• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of Ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of Net Ecosystem Exchange (NEE), an Ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of Ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed Ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within Ecosystems, and has the potential to significantly regulate Ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of Ecosystems in changing environments and benchmarking global models.
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Thermal adaptation of Net Ecosystem Exchange
2011Co-Authors: Wenping Yuan, Shuli Niu, Yiqi Luo, S. Liang, P. Stoy, J. Chen, A. R. Desai, A. Lindroth, C. M. GoughAbstract:Abstract. Thermal adaptation of gross primary production and Ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of Net Ecosystem Exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland Ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (Tb) at which Ecosystem transferring from carbon source to sink and optimal temperature (To) at which carbon uptake is maximized. Tb was strongly correlated with annual mean air temperature. To was strongly correlated with mean temperature during the Net carbon uptake period across the study Ecosystems. Our results suggested that Ecosystem CO2 flux switched from source to sink when air temperature reached annual mean temperature in spring and reached maximum uptake at mean temperature of the Net carbon uptake period. Our results imply that the Net Ecosystem Exchange of carbon adapt to the temperature across the geographical range due to intrinsic connections between vegetation primary production and Ecosystem respiration.
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Thermal adaptation of Net Ecosystem Exchange
Biogeosciences, 2011Co-Authors: Wenping Yuan, Shuli Niu, Yiqi Luo, S. Liang, P. Stoy, J. Chen, A. R. Desai, A. Lindroth, C. M. Gough, R. CeulemansAbstract:Thermal adaptation of gross primary production and Ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of Net Ecosystem Exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland Ecosystems located at latitudes ranging from similar to 29 degrees N to 64 degrees N. The response curves were used to define two critical temperatures: transition temperature (T(b)) at which Ecosystem transfer from carbon source to sink and optimal temperature (T(o)) at which carbon uptake is maximized. T(b) was strongly correlated with annual mean air temperature. T(o) was strongly correlated with mean temperature during the Net carbon uptake period across the study Ecosystems. Our results imply that the Net Ecosystem Exchange of carbon adapts to the temperature across the geographical range due to intrinsic connections between vegetation primary production and Ecosystem respiration.
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Latitudinal patterns of magnitude and interannual variability in Net Ecosystem Exchange regulated by biological and environmental variables
Global Change Biology, 2009Co-Authors: Wenping Yuan, Yiqi Luo, Xuhui Zhou, Reinhart Ceulemans, Ram Oren, Ivan A. Janssens, Andrew D. Richardson, Sebastiaan Luyssaert, Thomas Grünwald, Marc AubinetAbstract:Over the last two and half decades, strong evidence showed that the terrestrial Ecosystems are acting as a Net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in Net Ecosystem Exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29°N to ~64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is Ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
Patrick M. Crill - One of the best experts on this subject based on the ideXlab platform.
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Net Ecosystem Exchange of Carbon dioxide in a Temperate Poor Fen: a Comparison of Automated and Manual Chamber Techniques
Biogeochemistry, 2005Co-Authors: Elizabeth H. Burrows, Jill L. Bubier, Andrew Mosedale, George W. Cobb, Patrick M. CrillAbstract:We used five analytical approaches to compare Net Ecosystem Exchange (NEE) of carbon dioxide (CO_2) from automated and manual static chambers in a peatland, and found the methods comparable. Once per week we sampled manually from 10 collars with a closed chamber system using a LiCor 6200 portable photosynthesis system, and simulated four photosynthetically active radiation (PAR) levels using shrouds. Ten automated chambers sampled CO_2 flux every 3 h with a LiCor 6252 infrared gas analyzer. Results of the five comparisons showed (1) NEE measurements made from May to August, 2001 by the manual and automated chambers had similar ranges: −10.8 to 12.7 μ mol CO_2 m^−2 s^−1 and −17.2 to 13.1 μ mol CO_2 m^−2 s^−1, respectively. (2) When sorted into four PAR regimes and adjusted for temperature (respiration was measured under different temperature regimes), mean NEE did not differ significantly between the chambers ( p
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Net Ecosystem Exchange of Carbon Dioxide in a Temperate Poor Fen: A Comparison of Automated and Manual Chamber Techniques,
Biogeochemistry, 2005Co-Authors: Elizabeth H. Burrows, Jill L. Bubier, Andrew Mosedale, George W. Cobb, Patrick M. CrillAbstract:We used five analytical approaches to compare Net Ecosystem Exchange (NEE) of carbon dioxide (CO2) from automated and manual static chambers in a peatland, and found the methods comparable. Once pe ...