Ecological relevance of carbon isotope fractionation during dark respiration

对生物圈/大气CO2交换的功能理解对于全球气候变化具有重要意义。因此，生态系统吸收通量和呼吸通量及其相关碳库的研究已成为全球生态系统研究的主要目标。稳定的碳同位素δ13C比值为确定驱动生态系统呼吸过程的潜在机制提供了强有力的诊断工具。在生理尺度上，对植物暗呼吸过程中的同位素分馏已经有了透彻的了解，但对其在更大尺度上的影响知之甚少。很明显，这种分离的程度在不同的功能植物群之间存在很大差异，但关于其机制的实验证据仍然缺乏。本项目旨在通过结合代谢、全植物和生态系统方法，缩小暗呼吸过程中分馏机制的最新进展与其生态意义之间的差距。本研究将考虑叶片、芽和根代谢产物库的日动态，重点分析选定功能组呼吸δ13Cres的短期变化。在更大尺度上，δ 13cre的日动态可能的含义将通过评估叶片、全植物和生态系统尺度上的过程来评估，并使用成分质量平衡方法在自然地中海生态系统中进行评估。了解生态系统呼吸δ13C动态背后的过程对评估生态系统对全球变化的响应具有重要意义。

A functional understanding of biosphere/atmosphere CO2 exchange is important regarding global climate change. Investigation of ecosystem assimilatory and respiratory fluxes and associated carbon pools has thus, become a major goal in ecosystem research world-wide. Stable carbon isotope ratios δ13C provide a powerful diagnostic tool to identify the underiying mechanisms driving ecosystem respiratory processes. A thorough understanding of isotopic fractionation during dark respiration in plants has been achieved on the physiological scale, however much iess is known about its impact at larger scales. It has become evident that the extent of this fractionation varies substantially among different functional plant groups but experimental proof on the mechanisms is still lacking. This project aims to close the gap between recent advances on,mechanisms of fractionation during dark respiration and its ecological significance by combining metabolic, whole-plant and ecosystem approaches. This study will focus on the analysis of short-term variations of respiratory δ13Cres in selected functional groups considering diurnal dynamics of metabolite pools in leaves, shoots and roots. Possible implications of diurnal dynamics in δ13Cres at larger scales will be assessed by evaluating the processes at the leat whole-plant and the ecosystem scale using a component mass balance approach in a natural Mediterranean ecosystem. Understanding the processes behind the dynamics of δ13C of ecosystem respiration has significant implications for the evaluation of ecosystem response to global change.