Carbon Flux Data Research Articles

Potential of constructing all‐encompassing soil–plant‐atmosphere‐continuum stations and datasets from meteorological, flux, soil moisture station networks and plant‐relevant observations

AbstractThe establishment of SPAC (soil–plant‐atmosphere continuum) stations is essential for comprehensive monitoring of land‐atmosphere interactions and ecological and hydrological processes. This paper addresses the critical limitations of existing observation networks, which often rely on single‐aspect observations, resulting in insufficient data for a holistic understanding of SPAC dynamics. Specifically, SPAC stations provide critical multi‐variable observations that enhance process‐based model calibration and physical constraints and improve the empirical basis of data‐driven models. Advanced technologies such as machine learning and remote sensing are proposed to transform current weather and soil moisture stations into quasi‐SPAC sites capable of estimating carbon and water flux data. Additionally, the strategic placement of new SPAC sites in regions projected to be sensitive to future climate change and climate risks, as indicated by models such as CMIP6, is recommended. Furthermore, promoting comprehensive observational systems like Europe's Integrated Carbon Observation System (ICOS) in other regions, establishing a unified management framework and coordinating the upgrading of existing global observation networks are essential steps. Ultimately, the proposed enhancements will advance global ecological and hydrological studies, providing a more integrated and accurate understanding of the SPAC system and its responses to climate variability.

Snow cover duration delays spring green-up in the northern hemisphere the most for grasslands

Snow is an important factor controlling vegetation functions in high latitudes/altitudes. However, due to the lack of reliable in-situ measurements, the effects of snow on vegetation phenology remains poorly understood. Here, we examine the effects of snow cover duration (SCD) on the start of growing season (SOS) for different vegetation types. SOS and SCD were extracted from in-situ carbon flux and albedo data, respectively, at 51 eddy covariance flux sites in the northern mid-high latitudes. The effects of SCD on SOS vary substantially among different vegetation types. For grassland, preseason SCD outperforms other factors controlling grassland SOS. However, for forests and cropland, the preseason air temperature is the dominant factor in controlling SOS. Preseason SCD mainly influences the SOS by regulating preseason air and soil temperature rather than soil moisture. The CMIP6 Earth system models (ESMs) fail to capture the effect of SCD on SOS. Thus, Random Forest (RF) models were established to predict future SOS changing trends considering the effect of SCD. For grassland and evergreen needleleaf forest, the projected SOS advance rate is slower when SCD is considered. These findings can help us better understand impacts of snow on vegetation phenology and carbon-climate feedbacks in the warming world.

The influence patterns of carbon flux in different climatic zones in China —Based on the complex network approach

Research on ecosystem carbon flux can provide important methodological and strategic support for climate change mitigation. The existing studies focus on the calculation of carbon flux, ignoring the intertwined effects between regions. The quantification and analysis of the interaction patterns of carbon flux is crucial for understanding the global carbon cycle process, forecasting and coping with climate change. In this study, carbon flux network model sequences are established based on complex network theory using carbon flux data spanning from December 1, 2005, to November 30, 2020. The time delay effect is introduced to accurately quantify the influence patterns of carbon flux within climate zones across China. The findings indicate that the probability distribution function of the link weights during the various seasons of each year exhibits a bimodal distribution with distinct positive and negative components. The delay probability distribution function reveals the significant impact of delay effects, which are especially pronounced and mostly significant long-term lag effects in nodes with negative weights. Further, the results of the interactions of carbon flux among climate zones demonstrate that changes in carbon flux in the plateau and southern temperate regions have either positive or negative impacts on other climate zones. Therefore, controlling carbon flux changes in these climatic zones can effectively optimize the distribution of carbon flux. The modeling framework and results presented in this paper provide useful insights for the regulation and distribution optimization of carbon flux in China.

Using Free Air CO2 Enrichment data to constrain land surface model projections of the terrestrial carbon cycle

Abstract. Predicting the responses of terrestrial ecosystem carbon to future global change strongly relies on our ability to model accurately the underlying processes at a global scale. However, terrestrial biosphere models representing the carbon and nitrogen cycles and their interactions remain subject to large uncertainties, partly because of unknown or poorly constrained parameters. Parameter estimation is a powerful tool that can be used to optimise these parameters by confronting the model with observations. In this paper, we identify sensitive model parameters from a recent version of the ORgainzing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) land surface model that includes the nitrogen cycle. These sensitive parameters include ones involved in parameterisations controlling the impact of the nitrogen cycle on the carbon cycle and, in particular, the limitation of photosynthesis due to leaf nitrogen availability. We optimise these ORCHIDEE parameters against carbon flux data collected on sites from the FLUXNET network. However, optimising against present-day observations does not automatically give us confidence in future projections of the model, given that environmental conditions are likely to shift compared to the present day. Manipulation experiments give us a unique look into how the ecosystem may respond to future environmental changes. One such type of manipulation experiment, the Free Air CO2 Enrichment (FACE) experiment, provides a unique opportunity to assess vegetation response to increasing CO2 by providing data under ambient and elevated CO2 conditions. Therefore, to better capture the ecosystem response to increased CO2, we add the data from two FACE sites to our optimisations, in addition to the FLUXNET data. We use data from both CO2 conditions of FACE, which allows us to gain extra confidence in the model simulations using this set of parameters. We find that we are able to improve the magnitude of modelled productivity. Although we are unable to correct the interannual variability fully, we start to simulate possible progressive nitrogen limitation at one of the sites. Using an idealised simulation experiment based on increasing atmospheric CO2 by 1 % yr−1 over 100 years, we find that optimising against only FLUXNET data tends to imply a large fertilisation effect, whereas optimising against FLUXNET and FACE data (with information about nutrient limitation and acclimation of plants) decreases it significantly.

Projected decline in the strength of vegetation carbon sequestration under climate change in India

Tropical vegetation plays a critical role in terrestrial carbon budget and supply many ecological functions such as carbon sequestration. In recent decades, India has witnessed an increase in net primary productivity (NPP), an important measure of carbon sequestration. However, uncertainties persist regarding the sustainability of these land carbon sinks in the face of climate change. The enhanced NPP is driven by the strong CO2 fertilization effect (CFE), but the temporal patterns of this feedback remain unclear. Using the carbon flux data from the Earth System Models (ESMs), an increasing trend in NPP was observed, with projections of NPP to 2.00 ± 0.12 PgCyr-1 (25 % increase) during 2021-2049, 2.36 ± 0.12 PgCyr-1 (18 % increase) during 2050-2079, and 2.67 ± 0.07 PgCyr-1 (13 % increase) during 2080-2099 in Indian vegetation under SSP585 scenario. This suggests a significant decline in the NPP growth rate. To understand the feedback mechanisms driving NPP, the relative effects of CFE and warming were analyzed. Comparing simulations from the biogeochemically coupled model (BGC) with the fully coupled model, the BGC model projected a 74.7 % increase in NPP, significantly higher than the 55.9 % increase projected by the fully coupled model by the end of the century. This indicates that the consistent increase in NPP was associated with CO2 fertilization. More importantly, results reveal that the decrease in the NPP growth rate was due to the declining contribution of CFE at a rate of -0.62 % per 100 ppm CO2 increase. This decline could be attributed to factors such as nutrient limitations and high temperatures. Additionally, significant shifts in the strength of carbon sinks in offsetting the CO2 emissions were identified, decreasing at a rate of -1.15 % per decade. This decline in the strength of vegetation carbon sequestration may increase the societal dependence on mitigation measures to address climate change.

2019–2021年黄土高原典型粮草复合生态系统日通量数据集

As a typical ecosystem type on the Loess Plateau, the grain and grass complex ecosystem plays a vital role in maintaining regional food production and animal husbandry development. Understanding the characteristics of carbon water flux and energy partitioning in the grain and grass complex ecosystem on the Loess Plateau is of great significance for understanding the regional climate, carbon water cycle and its coupling process on the Loess Plateau. The dataset contains the carbon and water flux data accumulated by the National Field Scientific Observation and Research Station of Qingyang Grassland Agricultural Ecosystem, Lanzhou University, from January 2019 to December 2021. The data indexes include net ecosystem exchannge (NEE) of CO2, total ecosystem productivity (GEP), ecosystem respiration (RE), evapotranspiration (ET), latent heat flux (H), net radiation (Rn), and rainfall (P). The studied ecosystem is a grain and grass complex ecosystem, which belongs to the typical agricultural production type of the Loess Plateau and has strong regional representation. The dataset was prepared in strict accordance with international flux observation technical standards from field observation, data warehousing, and quality control to flux calculation. The comprehensive and high-quality data in this dataset can provide a foundation for research on crop production, efficient use of water resources, carbon source and sink management, and response to global climate change in the Loess Plateau.

Warming, rather than drought, remains the primary factor limiting carbon sequestration

Steppe ecosystems in arid and semiarid regions are particularly sensitive to climate change and strongly regulate the global carbon balance. However, carbon fluxes respond differently to climate change in different growing seasons, and the mechanism of this control is not yet clear. Therefore, we (i) obtained carbon flux data observed by a field eddy station in Inner Mongolia from 2006 to 2021; (ii) investigated the constraint effects of climatic factors on carbon fluxes; (iii) explored the response mechanisms of carbon fluxes to coupled changes in temperature and moisture; (iv) investigated the adaptation of steppe ecosystem to changes in temperature and drought. The results showed that (i) the steppe ecosystem was a carbon sink, with an average annual carbon fixation of 73.55 g C m−2 yr−1 and a roughly N-shaped carbon sink accumulation process within one year. (ii) The constraint effect of temperature and Vapor Pressure Deficit (VPD) on Net Ecosystem Productivity (NEP) and Gross Primary Productivity (GPP) was parabolic, with a clear optimum point. (iii) Temperature and moisture in the soil played a greater role in ecosystem carbon sequestration. Soil Water Content (SWC) could alleviate the inhibitory effect of temperature changes on the carbon sequestration of ecosystem. (iv) This ecosystem was capable of adapting well to changes in temperature and drought. However, warming, rather than drought, remains the primary factor limiting carbon sequestration. Specifically, it was GPP that drives the adaptation of ecosystem carbon sequestration to changes in temperature and drought, rather than Ecosystem Respiration (RECO). Although the steppe ecosystem has a good adaptation to changes in temperature and drought, it is still in the boundary region of warming. We hope that our study will deepen our comprehensive understanding of the relationship between temperature and moisture and ecosystem carbon fluxes and provide evidence for steppe ecosystem adaptation to climate change.

A dataset of soil carbon flux in Xishuangbanna tropical rainforest ecosystem from 2003 to 2008

Long-term and large-scale carbon flux data supports research on key processes of the global carbon and water cycle. Soil is the largest carbon pool in the terrestrial ecosystem. Small variations in soil carbon can significantly impact the carbon budgets of terrestrial ecosystems. Tropical forest is a crucial carbon sink in the world. However, there have been some reports indicating a decrease in soli carbon levels, potentially approaching neutrality, as a result of soil carbon degradation caused by global changing. Thus, the long-term and continuous observation of soil carbon flux is of great significance for evaluating the role of soil carbon in the tropical carbon cycle. ChinaFLUX Observation and Research Network (ChinaFLUX) has not only conducted the observation and research on carbon flux by using vorticity correlation technology, but also carried out the long-term observation and research on surface CO2 flux by using the box method. In this dataset, we collected and sorted out the soil CO2 emission flux data and conventional meteorological data of Xishuangbanna tropical rain forest ecosystem from January 2003 to August 2008 according to the static box observation method and data quality control management of greenhouse gas emissions. The dataset consists of three types of files at daily, monthly and yearly scales, covering surface CO2 flux, pressure, atmospheric temperature, soil temperature (5 cm) and soil water content (5 cm). It is expected to provide essential data for estimating carbon balance and understanding carbon cycle processes at both tropical and global scales.

Long‐term herbivore removal experiments reveal how geese and reindeer shape vegetation and ecosystem CO2‐fluxes in high‐Arctic tundra

Abstract Given the current rates of climate change, with associated shifts in herbivore population densities, understanding the role of different herbivores in ecosystem functioning is critical for predicting ecosystem responses. Here, we examined how migratory geese and resident, non‐migratory reindeer—two dominating yet functionally contrasting herbivores—control vegetation and ecosystem processes in rapidly warming Arctic tundra. We collected vegetation and ecosystem carbon (C) flux data at peak plant growing season in the two longest running, fully replicated herbivore removal experiments found in high‐Arctic Svalbard. Experiments had been set up independently in wet habitat utilised by barnacle geese Branta leucopsis in summer and in moist‐to‐dry habitat utilised by wild reindeer Rangifer tarandus platyrhynchus year‐round. Excluding geese induced vegetation state transitions from heavily grazed, moss‐dominated (only 4 g m−2 of live above‐ground vascular plant biomass) to ungrazed, graminoid‐dominated (60 g m−2 after 4‐year exclusion) and horsetail‐dominated (150 g m−2 after 15‐year exclusion) tundra. This caused large increases in vegetation C and nitrogen (N) pools, dead biomass and moss‐layer depth. Alterations in plant N concentration and CN ratio suggest overall slower plant community nutrient dynamics in the short‐term (4‐year) absence of geese. Long‐term (15‐year) goose removal quadrupled net ecosystem C sequestration (NEE) by increasing ecosystem photosynthesis more than ecosystem respiration (ER). Excluding reindeer for 21 years also produced detectable increases in live above‐ground vascular plant biomass (from 50 to 80 g m−2; without promoting vegetation state shifts), as well as in vegetation C and N pools, dead biomass, moss‐layer depth and ER. Yet, reindeer removal did not alter the chemistry of plants and soil or NEE. Synthesis. Although both herbivores were key drivers of ecosystem structure and function, the control exerted by geese in their main habitat (wet tundra) was much more pronounced than that exerted by reindeer in their main habitat (moist‐to‐dry tundra). Importantly, these herbivore effects are scale dependent, because geese are more spatially concentrated and thereby affect a smaller portion of the tundra landscape compared to reindeer. Our results highlight the substantial heterogeneity in how herbivores shape tundra vegetation and ecosystem processes, with implications for ongoing environmental change.

The Divergent Resistance and Resilience of Forest and Grassland Ecosystems to Extreme Summer Drought in Carbon Sequestration

It is projected that extreme drought events will become more frequent and more severe across many regions of the globe by the end of the 21st century. Despite the substantial efforts that have been made to explore the impacts of droughts on terrestrial ecosystems, our understanding of the response of diverse ecosystems, including resistance and resilience, remains unclear. A total of 16 site years of eddy covariance-based carbon flux data were used to reveal the different responses of forest and grassland ecosystems to two extreme summer droughts. We found that the carbon fluxes of the forest, namely gross primary productivity (GPP), ecosystem respiration (Re), and the net ecosystem carbon exchange (NEE), exhibited distinct seasonal patterns with a single peak. However, GPP and NEE of grassland showed multiple peaks owing to hay harvesting throughout one year. Meanwhile, all climate factors jointly affected the seasonal dynamics in the NEE of the forest, whereas solar radiation only dominated the variability in the NEE of grassland. Moreover, the optimal response relationship was quadratic between the vapor pressure deficit (VPD) and the NEE, with the thresholds being 5.46 and 5.84 for forest and grassland, respectively. Owing to the large increase in VPD during the droughts of 2003 and 2018, the carbon sequestration of forest and grassland reduced sharply and even altered from carbon sink to carbon source. Compared with grassland, forest GPP showed stronger resistance with weaker resilience to droughts. However, larger resilience appeared for both forest and grassland NEE relative to their resistance. All analyses reflect the different adaptive strategies among plant functional types, which is crucial to evaluate ecosystem carbon sequestration to overcome future climate change.

New data‐driven method for estimation of net ecosystem carbon exchange at meteorological stations effectively increases the global carbon flux data

Abstract The eddy covariance (EC) flux stations have great limitations in the evaluation of the global net ecosystem carbon exchange (NEE) and in the uncertainty reduction due to their sparse and uneven distribution and spatial representation. If the EC stations are linked with widely distributed meteorological stations using machine learning (ML) and remote sensing, it will play a big role in effectively improving the accuracy of the global NEE assessment and reducing uncertainty. In this study, we developed a framework for estimating NEE at meteorological stations. We first optimized the hyperparameters and input variables of the ML model based on the optimization method called an adaptive genetic algorithm. Then, we developed 566 random forest (RF)‐based NEE estimation models by the strategy of spatial leave‐out‐one cross‐validation. We innovatively established the Euclidean distance‐based accuracy projection algorithm of the R square (R2), which could test the accuracy of each model to estimate the NEE of the specific flux at the weather station. Only the model with the highest R2 was selected from the models with a prediction accuracy of R2 > 0.5 for the specific meteorological stations to estimate its NEE. 4674 out of 10,289 weather stations around the world might match at least one of the 566 NEE estimation models with a projected accuracy of R2 > 0.5. The NEE estimation models we screened for the meteorological stations showed a reliable performance and a higher accuracy than the former studies. The NEE values of the most (96.9%) screened meteorological stations around the world are negative (carbon sink) and most (65.3%) of those showed an increasing trend in the mean annual NEE (carbon sink). The NEE dataset produced at the meteorological stations could be used as a supplement to the EC observations and quasi‐observation data to assess the NEE products of the global grid. The NEE dataset is publicly available via the figshare with https://doi.org/10.6084/m9.figshare.20485563.v1.

Fluxbots: A Method for Building, Deploying, Collecting and Analyzing Data From an Array of Inexpensive, Autonomous Soil Carbon Flux Chambers

AbstractSoil carbon flux rates are a crucial metric of carbon cycling that contribute to calculating an ecosystem's carbon budget, and thus whether it is a source or sink of atmospheric carbon dioxide. However, soil carbon flux datasets are frequently low‐resolution across either space or time, limiting our abilities to identify small‐scale ecological contexts that influence soil carbon dynamics. Existing datasets are distributed unevenly, with some soil carbon‐rich regions (like tropical grasslands) significantly understudied. We developed an autonomous, inexpensive, do‐it‐yourself (DIY) soil carbon flux chamber (a “fluxbot”) and data processing software. We deployed a distributed array of 12 fluxbots in a long‐term experiment in a central Kenyan savanna where it has been logistically impossible to collect high‐resolution soil carbon flux data. With this array we collected over 10,000 individual flux estimates over almost two months, spanning the end of a dry season and the start of a wet season. With our successful deployment in situ, we demonstrate the potential for low‐cost, autonomous, DIY sensors in improving resolution of soil carbon flux datasets (particularly in under‐studied or logistically challenging systems). If implemented widely, such an improvement in data collection capacities could improve our understanding of ecological and climatic drivers of soil carbon flux dynamics on the local to global scale.

Carbon exchange of forest plantations: global patterns and biophysical drivers

Plantation has large carbon sequestration potential, and it plays an important role in mitigating global warming. However, the responses of carbon fluxes to biophysical factors across plantation sites are still not clear. We synthesized carbon flux data measured by the eddy covariance method over the plantations at the global scale to explore the shifts of carbon exchange with latitude, discuss the link of carbon fluxes with biophysical variables, and compare the difference in carbon sequestration between needleleaf and broadleaf plantations. Annual net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (ER) across all plantations were 353±27, 1762±60 and 1385±46 g C m−2 yr−1, respectively. The mean annual NEP of needleleaf biomes was similar to that of broadleaf biomes. GPP and ER were 48% and 64% larger at needleleaf forests than at broadleaf forests. Annual NEP, GPP and ER decreased with the increase of latitude significantly. At the half-hourly scale, the increase of diffuse radiation enhanced carbon assimilation of needleleaf and broadleaf biomes remarkably. On the annual scale, both GPP and NEP were sensitive to mean annual temperature (MAT) and leaf area index (LAI). Annual precipitation was the dominant factor regulating the variability of GPP and ER, and it explained 34% and 47% of the variation in GPP and ER, respectively. The extension in growing season length (GSL) and rising soil water content (SWC) enhanced ecosystem photosynthesis and respiration of planted forests. However, the effect of GSL and SWC on net carbon uptake was not remarkable. These results highlight the importance of biophysical factors in regulating carbon dynamics of the plantations, and contribute to understanding of the differences in carbon sequestration between needleleaf and broadleaf biomes.

Study of a calibration system for soil respiration measurement chambers

Purpose. Soil respiration measurement is an important component of the global carbon cycle assessment. To effectively validate the measurement performance of the monitoring instruments and provide accurate carbon flux data, a new flux-monitoring gas-chamber calibration system was investigated. Method. In an environmentally controlled laboratory, a concentration calculation calibration system, mass calculation calibration system, and flow calculation calibration system were used to quantify soil CO2 emissions. The measurement performance of the soil-respiration monitoring gas chamber was investigated, and the strengths and weaknesses of each calibration system were examined. Results. The unsteady-state flow chamber and steady-state chamber measurements had fewer errors and provided better results than the unsteady-state nonflow chamber. The measured values of the closed chamber were low, whereas the measured values of the open chamber were occasionally high and low. For calibration systems, the concentration calculation system is easy to operate; however, the reference flux values are unstable, and the mass calculation system allows for different gas transport mechanisms. However, it is complex to operate and it is difficult to control the air pressure in the diffusion chamber. The calibration process of the flow calculation system was stable and easy to operate; however, the experimental time was long, and the CO2 gas consumption was high. However, for the calibration effect, the optimal calibration system was the flow-meter algorithm. Conclusion. This study proposes a better calibration method for the soil CO2 flux gas chamber, which is conducive to improving the measurement accuracy of the instrument, and provides new ideas for the calibration of other environmental gas monitoring instruments.

Environmental controls on water use efficiency in a hilly tea plantation in southeast China

Knowledge of water use efficiency (WUE) at the ecosystem level is imperative as it is a critical ecophysiological index reflecting the coupling processes between carbon sequestration and water consumption. However, the temporal patterns of WUE and their underlying regulating factors during different seasons in tea plantations, which are under intense pruning practice, remain poorly understood. Based on carbon and water vapor flux data obtained by the eddy covariance technique in a subtropical hilly tea plantation in southeast China during 2014–2018, this study analyzed the seasonal variations in gross primary productivity (GPP), evapotranspiration (ET) and ecosystem WUE, and discussed the response of GPP, ET and WUE to environmental variables during different seasons. The results showed that the mean annual GPP, ET and WUE ranged from 1426.61 ~ 1896.05 g C m−2, 607.05 ~ 805.83 mm and 2.22 ~ 2.68 g C kg−1 H2O, respectively. At the daily time scale, GPP and ET responded significantly and positively to variations in air temperature (Ta), water vapor pressure deficit (VPD), and net radiation (Rn) in both the pruning season and late growing season, but daily WUE had a significantly negative response to variations in Ta, VPD and Rn. Rn was identified as the dominant factor in regulating GPP and ET during both the pruning season and late growing season, while the dominant factor controlling daily variations in WUE was VPD during the pruning season and Ta during the late growing season. Such results were mainly due to the divergent responses of carbon assimilation and water loss to different environmental variations and management strategies. These findings highlighted the importance of understanding the coupled processes between carbon assimilation and water loss in tea plantations.

Weakening of carbon sink on the Qinghai–Tibet Plateau

Cold regions contain a large amount of soil organic carbon, and the warming-accelerated loss of this carbon pool could cause important feedback to climatic change. The changes of carbon budgets in cold regions are poorly quantified especially for the Qinghai–Tibet Plateau (QTP) due to limited field observation data. By considering the soil freeze–thaw process and establishing new plant functional types with localized parameters, we used the Integrated Biosphere Simulator (IBIS) model to simulate the changes of carbon budget on the QTP during 1980–2016. The model was calibrated and validated using carbon flux data from eddy covariance observations at 16 sites. The results showed that the QTP has assimilated 43.16 Tg C/yr during 1980–2016, with permafrost and non-permafrost regions accounting for approximately 15% and 85% of the carbon sink, respectively. During the past four decades, the gross primary production and ecosystem respiration have increased by 1.74 and 2.04 Tg C/yr2, resulting in that the carbon sink on the QTP has weakened during 1980–2016. Moreover, the weakening of carbon sink is more pronounced in the non-permafrost regions. We project that the ecosystems will release 12.30 and 24.40 Tg C by 2080–2100 under the moderate and high shared socio-economic pathways (SSP 370 and SSP 585), respectively. This could largely offset the carbon sink and even shift the carbon sink to carbon source on the QTP.

大气气溶胶对北京杨树人工林生态系统生产力的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 大气气溶胶对北京杨树人工林生态系统生产力的影响 DOI: 10.5846/stxb202005281383 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31872711） Effects of atmospheric aerosols on the ecosystem productivity of a poplar plantation in Beijing Author: Affiliation: Fund Project: Impact Mechanisms of Atmospheric Aerosols on Forest Ecosystem Carbon and Water Coupling 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大气气溶胶可以影响到达地面的太阳辐射，进而影响植物光合作用和生态系统生产力，乃至区域上的碳收支。为探究北京地区气溶胶对杨树人工林生态系统生产力的影响，利用2006-2009年北京大气气溶胶数据结合北京大兴杨树人工林涡度相关系统监测的辐射、碳通量等数据，分析了气溶胶对散射辐射、光能利用效率（LUE）、生态系统初级生产力（GPP）的影响，并利用通径分析方法探究了气溶胶和生态环境因子对GPP的直接和间接影响。结果表明，北京市气溶胶光学厚度（AOD）具有明显的季节变化特征：春、夏两季大于秋、冬季，夏季气溶胶光化学厚度最大。大气气溶胶显著影响了地表辐射组分以及温度、湿度环境因子，随着AOD从0增大到3，总辐射减小了43.63%，散射辐射增加132.26%，散射辐射比例增大了2.55倍，而相对湿度增大48.52%，日温差增大3℃左右。当生态系统受水分胁迫时，气溶胶对生态系统生产力无显著影响，当生态系统处于非水分胁迫时，杨树人工林生态系统光能利用效率和生产力随着气溶胶浓度增大先增大后减小，当AOD为1.0-1.6时，GPP维持在较高的水平，当AOD>2.5时，GPP显著减小且小于背景气溶胶（AOD<0.4）的GPP。通径分析表明，水分胁迫条件下，气溶胶对杨树人工林生态系统生产力的间接影响很小；非水分条件下，散射辐射对生态系统生产力影响最大，气溶胶可以通过增大散射光施肥效应来增大生态系统生产力。不同的水分条件下气溶胶对杨树人工林生态系统的影响不同，非水分胁迫条件下适宜的气溶胶增大杨树人工林生态系统的生产力，严重的气溶胶污染（AOD>1.5）则导致杨树生态系统生产力下降。 Abstract:Atmospheric aerosols can affect the solar radiation reaching the ground, which in turn affects plant photosynthesis and ecosystem productivity, and even regional carbon balance. With the further development of global change, atmospheric aerosols pollution and drought stress coexist in some regions, and the high frequency and long duration of drought stress may lead to the conversion of ecosystems from carbon sinks to carbon sources. However, little is known about whether atmospheric aerosols can increase ecosystem productivity when the ecosystem are under water stress. Therefore, in this study we investigated the effects of atmospheric aerosols on diffuse radiation, light utilization efficiency (LUE) and the gross primary productivity (GPP) of poplar plantation under different water conditions in Beijing. The direct and indirect effects of atmospheric aerosols and ecological factors on GPP were explored by the path analysis method, which used the atmospheric aerosols data from 2006 to 2009 and combined with the radiation and carbon flux data monitored by Eddy covariance system in Daxing poplar in Beijing. The results showed that Beijing's atmospheric optical depth (AOD) had obviously seasonal change characteristics. The AOD was higher in spring and summer than that in autumn and winter, and the AOD was the largest in summer. The atmospheric aerosols had significant effects on radiation and micrometeorological factors. With the increase of AOD from 0 to 3, photosynthetically active radiation (PAR) decreased by 43.63%, diffuse radiation increased by 170%, and the fraction of diffuse radiation increased by 2.55 times, while the relative humidity increased by 48.52% and daily temperature difference increased about 3℃. When the ecosystem was under moisture stress, the atmospheric aerosols had no effect on the GPP. When the ecosystem was under non-moisture stress, the LUE and GPP of poplar plantation ecosystem increased first and then decreased with the increase of aerosol concentration. When the AOD was 1.0-1.6, the GPP was maintained at a high level. When the AOD>2.5, the GPP significantly decreased and less than the GPP of the background atmospheric aerosol (AOD<0.4). The path analysis showed that the indirect effect of atmospheric aerosols on ecosystem productivity of poplar plantation was not significant under water stress, the diffuse radiation had the greatest influence on the GPP, and the atmospheric aerosols could increase the ecosystem productivity by increasing diffuse fertilization effect under non-moisture stress. Overall, the atmospheric aerosols had different effects on poplar plantation ecosystem under different water conditions. The suitable atmospheric aerosols could increase the productivity of poplar plantation ecosystems, while severe atmospheric aerosols pollution (AOD>1.5) led to a decrease in poplar ecosystem productivity under non-water stress conditions. 参考文献 相似文献 引证文献

Quantifying the variability in water use efficiency from the canopy to ecosystem scale across main croplands

Current, how to use limited water resources efficiently and improve agricultural water use efficiency, has become one of the greatest challenges for global food security. In this study, multiple site-years of carbon and water flux data across the major crops including maize, winter wheat and soybean, were used to quantify the variability in canopy-scale transpiration (T), ecosystem-scale evapotranspiration (ET) as well as the associated water use efficiencies (WUET and WUEET). On the basis of ET partitioning, the results indicated that the transpiration ratio–T/ET as well as T and ET exhibited an obvious single-peak seasonal pattern across the typical croplands. However, at the early and late growing stages, there existed large discrepancies in T and ET owing to low vegetation coverage, while T and ET were very close during the peak period. Among them, maize exhibited the largest T/ET by 0.50 ± 0.12, followed by soybean of 0.43 ± 0.08 and winter wheat of 0.38 ± 0.09, respectively. Furthermore, the coupling relationships between gross primary productivity (GPP) and water fluxes including T and ET changed from linear to nonlinear. The study also found that the variability in WUET and WUEET were not consistent. Specifically, WUEET showed distinct seasonal characteristic whereas WUET kept constant as a plateau almost throughout the growth period, which reflected the inherent physiological property controlled by plant stomata at the canopy scale. Among these crops, maize exhibited the largest WUET and WUEET (5.30 ± 0.89 and 2.48 ± 1.14 g C kg−1 H2O), followed by winter wheat (4.97 ± 1.52 and 2.35 ± 0.64 g C kg−1 H2O) and soybean (4.88 ± 1.59 and 1.89 ± 0.99 g C kg−1 H2O), respectively.

Drought occurrence and time‐dominated variations in water use efficiency in an alpine meadow on the Tibetan Plateau

AbstractUnder global climate change, more frequent and widespread droughts have dramatic impacts on the water and carbon cycles. Water use efficiency (WUE) is a commonly used indicator reflecting the trade‐off relationship between carbon sequestration and water consumption. Therefore, this study aims to clarify the variations in WUE and the effects of drought on WUE in sensitive alpine meadows on the Tibetan Plateau. Based on 6‐year (2013–2018) continuous carbon and water flux data observed by the eddy covariance system, WUE was calculated by gross ecosystem productivity (GEP)/evapotranspiration (ET). WUE followed a unimodal variation with time during growing seasons in the years without droughts. However, drought disrupted this pattern by its effects on the coupled relationship between carbon and water fluxes. Specifically, droughts showed divergent effects on WUE variations in different periods of the growing seasons. In the early‐growing seasons, droughts induced an increase in WUE. During this period, WUE was mainly regulated by temperature and leaf area index (LAI), and the GEP was low due to the smaller LAI. Therefore, the drought‐induced reduction in GEP was less than that in ET; thus, WUE increased. In the mid‐growing seasons, droughts depressed WUE. WUE was dominated by water conditions and the LAI during this period. When drought occurred, GEP decreased faster than ET, and hence, WUE decreased. In the late‐growing season, WUE was mainly driven by temperature and the LAI, but short‐term drought slightly enhanced WUE. These results are helpful in understanding the responses of fragile alpine ecosystems to future climate change.

Joint Influence Mechanism of Phenology and Climate on the Dynamics of Gross Primary Productivity: Insights From Temperate Deciduous Broadleaf Forests in North America

AbstractUnderstanding the influence mechanism of biotic and abiotic factors on the dynamics of gross primary productivity (GPP) is crucial to accurately simulate the terrestrial carbon cycle. Based on the carbon flux data, meteorological data (i.e., temperature, precipitation, vapor pressure deficit, and radiation) and phenological metrics (i.e., the date of greenup, maturity, senescence, and dormancy) collected from six North America temperate deciduous broadleaf forests (NAT‐DBF) sites, this study investigated the joint influence mechanism of phenology and climate on the dynamics of GPP by using commonality analysis and structural equation modeling. The results showed that precipitation, the date of maturity and senescence jointly dominated the dynamics of annual GPP in NAT‐DBF. The date of maturity and senescence rather than the date of greenup and dormancy were crucial phenological metrics that directly influenced the dynamics of annual GPP. There existed an important indirect influence path of temperature on the dynamics of annual GPP through regulating the date of maturity, while the direct influence of temperature on the dynamics of annual GPP was negligible. Precipitation not only directly influenced the dynamics of annual GPP, but also indirectly influenced the dynamics of annual GPP through regulating the date of senescence. Our study provides a process‐based understanding for the joint influence mechanism of meteorological factors and phenology on the dynamics of annual GPP, which is helpful for understanding the vegetation responses to climate change and improving the process‐based ecosystem models.