Drivers and mechanisms of 13C discrimination in Cleistogenes squarrosa (C4) - reducing uncertainties on bundle sheath leakiness

C4光合作用的能量效率受束鞘透性、叶片气体交换和13C组分数据的强烈影响，而束鞘透性通常用13C判别的Farquhar模型的线性版本来评估。但是，线性法夸尔模型是对C4植物中Δ的全机械理论的简化，可能会在估计渗漏量时产生错误。特别是，光合作用后的碳同位素分馏可能会造成很大的误差，但尚未进行任何详细的研究。本项目旨在提高对控制多年生草本植物Cleistgenes squarrosa的辨别和漏失的生态和发育/生理因素的了解。方锦蛇是C4群落中最重要的成员，在过去的几十年里，C4群落在蒙古草原上的分布非常广泛。它具有非同寻常的高度和可变的辨别力，这意味着非常高的(潜在的高度可变的)泄漏率。具体地说，我们将首次对这种C4物种在叶和林分尺度上的呼吸13C在明暗两级的分级进行系统的研究，并评估其对区分和估计渗漏的影响。这些实验是在专门的13CO2/12CO2气体交换中进行的，使用与生态相关的情景，测试关于环境驱动因素和植物和叶片发育阶段对区分和渗漏的影响的具体假设。

The energetic efficiency of C4 photosynthesis is strongly affected by bundle sheath leakiness, which is commonly assessed with the ‘linear version’ of the Farquhar model of 13C discrimination, and leaf gas exchange and 13C composition data. But, the linear Farquhar model is a simplification of the full mechanistic theory of Δ in C4 plants, potentially generating errors in the estimation of leakiness. In particular, post-photosynthetic C isotope fractionation could cause large errors, but has not been studied in any detail. The present project aims to improve the understanding of the ecological and developmental/physiological factors controlling discrimination and leakiness of the perennial grass Cleistogenes squarrosa. C. squarrosa is the most important member of the C4 community which has spread significantly in the Mongolia grasslands in the last decades. It has an unusually high and variable discrimination, which suggests very high (and potentially highly variable) leakiness. Specifically, we will conduct the first systematic study of respiratory 13C fractionation in light and dark at leaf- and stand-scale in this C4 species, and assess its effect on discrimination and estimates of leakiness. These experiments are conducted in specialized 13CO2/12CO2 gas exchange mesocosms using ecologically relevant scenarios, testing specific hypotheses on effects of environmental drivers and plant and leaf developmental stage on discrimination and leakiness.