Carbon allocation in plants - transport of newly assimilated carbon, carbon isotope fractionation and the relation to delta13C in respiratory CO2

生态系统呼吸通量可以由生态系统呼吸CO2的d13 C（d13 CR;通过Keeling图方法）结合微气象测量来计算。最近的研究表明，从整个生态系统中呼吸出的CO2中有很大一部分来自植被在过去几天内固定的碳。因此，所有的植被相关的过程，影响光合13 C歧视以及碳同位素分馏与分配新同化的有机碳从叶到根和根际将影响d13 CR。直到最近，d13 CR还不能以高分辨率及时常规测定。因此，在d13 C的基质呼吸的时间尺度内，从小时到天的变化，其对d13 C的呼吸CO2的影响有相当大的潜力混淆解释基林图。本研究的目的是评估最重要的过程中，可能会导致呼吸基质d13 C的时空变化的植物。在野外实验（用Eucalyptus delegatensis）和在受控条件下（用Ricinus communis）将解决的中心问题是：1）我们是否可以使用已知的Ci/Ca 1对有机碳的d13 C的影响来追踪碳运输速度，从而估计植物内特定d13 C信号的时间依赖性分布？2)在何种程度上的茎到根的运输影响d13 C的有机碳和什么是潜在的歧视的代谢过程？3)在植物中运输的糖的d13 C是否存在昼夜变化？4)在暗呼吸过程中是否存在碳同位素分馏？在芽、茎和根之间的分馏是否相似？此外，d13 C在植物体内的时空动态将与田间条件下d13 CR的时间动态相关。

Ecosystem respiratory fluxes can be calculated from d13C of ecosystem respiratory CO2 (d13CR; by the Keeling plot approach) combined with micrometeorological measurements. Recent studies showed that a large fraction of the CO2 respired from the whole ecosystem originates from carbon fixed within the last few days by the vegetation. As consequence, all vegetation-related processes that affect photosynthetic 13C discrimination as well as carbon isotope fractionation associated with allocation of newly assimilated organic carbon from the leaves to the roots and the rhizosphere will influence d13CR. Until recently d13CR could not be determined routinely with a high resolution in time. Consequently, variation in d13C of substrates for respiration within a time scale from hours to days and its influence on d13C of respired CO2 has considerable potential to confound interpretation of Keeling plots. This study is aimed at assessing the most important processes in plants that may cause spatial and temporal variation in d13C of respiratory substrates. The central questions that will be addressed in field experiments (with Eucalyptus delegatensis) and under controlled conditions (with Ricinus communis) are: 1) Can we use the known influence of Ci/Ca1 on d13C of organic carbon to trace carbon transport velocity and hence estimate the time-dependent distribution of a particular d13C signal within the plant? 2) To what extent does the shoot-to-root transport influence d13C of organic carbon and what are the underlying metabolic processes of a potential discrimination? 3) Are there day-night-variations in d13C of sugars transported in the plant? 4) Is there carbon isotope fractionation during dark respiration and is the fractionation comparable among shoots, stems and roots? In addition, the spatial and temporal dynamics in d13C within the plant will be related to the temporal dynamic of d13CR under field conditions.