Chair of Tree Physiology, University of Freiburg, Freiburg, Germany.
Plant Biol (Stuttg). 2011 Jan;13(1):115-25. doi: 10.1111/j.1438-8677.2010.00329.x.
Understanding environmental and physiological controls of the variations in δ(13) C of CO(2) respired (δ(13) C(R)) from different compartments of an ecosystem is important for separation of CO(2) fluxes and to assess coupling between assimilation and respiration. In a wheat field, over 3 days we characterised the temporal dynamics of δ(13) C(R) from shoots and roots, from the soil and from the whole agroecosystem. To evaluate the basis of potential variations in δ(13) C(R), we also measured δ(13) C in different organic matter pools, as well as meteorological and gas exchange parameters. We observed strong diel variations up to ca. 6% in shoot, root and soil δ(13) C(R), but not in δ(13) C of the putative organic substrates for respiration, which varied by not more than ca. 1% within 24 h. Whole ecosystem-respired CO(2) was least depleted in (13) C in the afternoon and most negative in the early morning. We assume that temporally variable respiratory carbon isotope fractionation and changes in fluxes through metabolic pathways, rather than photosynthetic carbon isotope fractionation, governs the δ(13) C of respired CO(2) at the diel scale, and thus provides insights into the metabolic processes related to respiration under field conditions.
了解生态系统不同部分 CO₂ 释放（δ¹³C(R)）的环境和生理控制因素的变化，对于分离 CO₂ 通量和评估同化与呼吸之间的耦合关系非常重要。在一个麦田里，我们在 3 天的时间里对来自地上部分和根系、土壤和整个农业生态系统的 δ¹³C(R)的时间动态进行了特征描述。为了评估 δ¹³C(R)潜在变化的基础，我们还测量了不同有机物质库中的 δ¹³C，以及气象和气体交换参数。我们观察到地上部分、根系和土壤 δ¹³C(R)的昼夜变化高达约 6%，但呼吸的潜在有机底物的 δ¹³C 变化不超过 24 小时内约 1%。整个生态系统呼吸的 CO₂ 在下午的碳同位素分馏最少，在清晨的碳同位素分馏最负。我们假设，在时间上变化的呼吸碳同位素分馏和代谢途径通量的变化，而不是光合作用碳同位素分馏，控制着昼夜尺度上呼吸 CO₂ 的 δ¹³C，从而为田间条件下与呼吸相关的代谢过程提供了见解。
