Carbon dioxide and water vapor exchange in a warm temperate grassland
Carbon dioxide and water vapor exchange in a warm temperate grassland
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DOI：
10.1007/s00442-003-1388-z
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发表时间：
2003
期刊：
影响因子：
2.7
通讯作者：
K. Novick;P. Stoy;G. Katul;D. S. Ellsworth;M. Siqueira;J. Juang;Ram Oren
中科院分区：
文献类型：
--
作者：
K. Novick;P. Stoy;G. Katul;D. S. Ellsworth;M. Siqueira;J. Juang;Ram Oren
草地覆盖了全球无冰陆地表面的约40%，但它们对当地和区域水和碳通量的贡献以及对干旱等气候扰动的敏感性仍然不确定。在这里，我们评估的方向和幅度的净生态系统碳交换（NEE）及其组成部分，生态系统碳同化（Ac）和生态系统呼吸（RE），在美国东南部的草地生态系统周期性干旱和收获使用涡度协方差测量和模型计算相结合。我们modeledAcand蒸散量（ET）使用一个大叶冠层计划结合生态生理和辐射传输的原则，并应用该模型来评估NEE和ET土壤水分动态和快速漂移的叶面积指数（LAI）草收获后的敏感性。模式结果密切配合涡度协方差通量估计每天，更长的时间步长。模型计算和涡动协方差估计都表明，草原在收获后立即成为大气碳的净来源，但叶面积指数的快速恢复在夏季维持了边际碳汇。然而，当一年中整合时，该草原生态系统是一个净C源（97 g C m−2a−1），这是由于大的Ac（− 1，202 g C m−2a−1）和RE（1，299 g C m−2a−1）通量之间的轻微不平衡。在测量期间，轻度干旱条件导致许多低土壤水分（θ<0.2 m3m−3）的情况，这通过降低气孔导度影响了Ac，从而影响了NEE。对于本实验，低θ对RE的影响较小。因此，气孔对碳的限制是该草地成为碳净源的主要原因。在没有土壤水分限制的情况下，模型计算表明，假设叶面积指数动态和生理特性不变，净碳汇为−65 g C m−2a− 1。这些结果和其他研究的结果表明，扰动的水文循环的C循环在草地生态系统中的关键决定因素。
Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE), in a southeastern United States grassland ecosystem subject to periodic drought and harvest using a combination of eddy-covariance measurements and model calculations. We modeledAcand evapotranspiration (ET) using a big-leaf canopy scheme in conjunction with ecophysiological and radiative transfer principles, and applied the model to assess the sensitivity of NEE and ET to soil moisture dynamics and rapid excursions in leaf area index (LAI) following grass harvesting. Model results closely match eddy-covariance flux estimations on daily, and longer, time steps. Both model calculations and eddy-covariance estimates suggest that the grassland became a net source of carbon to the atmosphere immediately following the harvest, but a rapid recovery in LAI maintained a marginal carbon sink during summer. However, when integrated over the year, this grassland ecosystem was a net C source (97 g C m−2a−1) due to a minor imbalance between largeAc(−1,202 g C m−2a−1) andRE(1,299 g C m−2a−1) fluxes. Mild drought conditions during the measurement period resulted in many instances of low soil moisture (θ<0.2 m3m−3), which influencedAcand thereby NEE by decreasing stomatal conductance. For this experiment, lowθhad minor impact onRE. Thus, stomatal limitations toAcwere the primary reason that this grassland was a net C source. In the absence of soil moisture limitations, model calculations suggest a net C sink of −65 g C m−2a−1assuming the LAI dynamics and physiological properties are unaltered. These results, and the results of other studies, suggest that perturbations to the hydrologic cycle are key determinants of C cycling in grassland ecosystems.