Disentangling drought-induced variation in ecosystem and soil respiration using stable carbon isotopes
Disentangling drought-induced variation in ecosystem and soil respiration using stable carbon isotopes
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DOI：
10.1007/s00442-010-1576-6
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发表时间：
2010-03
期刊：
影响因子：
2.7
通讯作者：
S. Unger;C. Máguas;J. Pereira;Luis M. I. Aires;T. David;C. Werner
中科院分区：
文献类型：
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作者：
S. Unger;C. Máguas;J. Pereira;Luis M. I. Aires;T. David;C. Werner
将碳通量测量与其同位素组成的信息结合起来，可以产生对生态系统碳动态的基于过程的理解。我们研究了在干旱加剧的时期，地中海橡树大草原所有主要成分(树木、林下植物、根和土壤微生物)的呼吸通量及其稳定的碳同位素组成(δ13C)的变化。在土壤、根和叶的呼吸(δ13Cres)的同位素组成中，我们发现了较大的干旱诱导和日动态。土壤呼吸是生态系统呼吸(RECO)的最大贡献者，表现出耗竭的同位素特征，并且没有随着干旱的加剧而显著变化，类似于生态系统呼吸的δ13CO2，这为稳定的碳源提供了证据，并且最近来自植物的光合作用的影响很小。叶片和根的δ13Cres的短期和日变化(分别高达8和4‰)符合：(1)最近关于光合作用后分离过程的假说；(2)随着同化率的下降和呼吸需求的增加，底物的变化；(3)干燥根中磷酸烯醇式丙酮酸羧化酶活性的降低，而光合作用辨别的改变不是观察到的δ13Cres变化的原因。我们应用了基于通量的质量平衡和基于通量的同位素质量平衡，在土壤尺度上产生了很好的一致性，而在生态系统尺度上的同位素质量平衡并不保守。这主要是由于生态系统尺度上的基林样地截获的不确定性造成的，这是由于CO2梯度较小，以及不同组分通量的δ13Cres存在较大差异。总体而言，稳定同位素为与干旱有关的生态系统碳动态变化提供了有价值的新见解，鼓励了未来的研究，但也突显了改进方法学的必要性，以理清Reco同位素组成的短期动态。
Combining C flux measurements with information on their isotopic composition can yield a process-based understanding of ecosystem C dynamics. We studied the variations in both respiratory fluxes and their stable C isotopic compositions (δ13C) for all major components (trees, understory, roots and soil microorganisms) in a Mediterranean oak savannah during a period with increasing drought. We found large drought-induced and diurnal dynamics in isotopic compositions of soil, root and foliage respiration (δ13Cres). Soil respiration was the largest contributor to ecosystem respiration (Reco), exhibiting a depleted isotopic signature and no marked variations with increasing drought, similar to ecosystem respired δ13CO2, providing evidence for a stable C-source and minor influence of recent photosynthate from plants. Short-term and diurnal variations in δ13Cresof foliage and roots (up to 8 and 4‰, respectively) were in agreement with: (1) recent hypotheses on post-photosynthetic fractionation processes, (2) substrate changes with decreasing assimilation rates in combination with increased respiratory demand, and (3) decreased phosphoenolpyruvate carboxylase activity in drying roots, while altered photosynthetic discrimination was not responsible for the observed changes in δ13Cres. We applied a flux-based and an isotopic flux-based mass balance, yielding good agreement at the soil scale, while the isotopic mass balance at the ecosystem scale was not conserved. This was mainly caused by uncertainties in Keeling plot intercepts at the ecosystem scale due to small CO2gradients and large differences in δ13Cresof the different component fluxes. Overall, stable isotopes provided valuable new insights into the drought-related variations of ecosystem C dynamics, encouraging future studies but also highlighting the need of improved methodology to disentangle short-term dynamics of isotopic composition ofReco.