The University of Sydney, School of Life and Environmental Sciences, Camden NSW, Australia.
Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia.
J Exp Bot. 2021 Oct 26;72(20):7191-7202. doi: 10.1093/jxb/erab320.
Mesophyll conductance (gm) is an important factor limiting photosynthesis. However, gm response to long-term growth in variable [CO2] is not well understood, particularly in crop plants. Here, we grew two cultivars of wheat (Halberd and Cranbrook), known to differ in gm under current environmental conditions, in four [CO2] treatments: glacial (206 μmol mol-1), pre-industrial (344 μmol mol-1), current ambient (489 μmol mol-1), and super-elevated (1085 μmol mol-1), and two water treatments (well-watered and moderate water limitation), to develop an evolutionary and future climate perspective on gm control of photosynthesis and water-use efficiency (WUE). In the two wheat genotypes, gm increased with rising [CO2] from glacial to ambient [CO2], but declined at super-elevated [CO2]. The responses of gm to different growth [CO2] also depend on water stress; however, the specific mechanism of gm response to [CO2] remains unclear. Although gm and gm/gsc (mesophyll conductance/stomatal conductance) were strongly associated with the variability of photosynthetic rates (A) and WUE, we found that plants with higher gm may increase A without increasing gsc, which increased WUE. These results may be useful to inform plant breeding programmes and cultivar selection for Australian wheat under future environmental conditions.
叶肉导度（gm）是限制光合作用的一个重要因素。然而，gm 对长期可变 [CO2] 条件下的响应尚不清楚，特别是在作物植物中。在这里，我们在四种 [CO2] 处理条件下种植了两个小麦品种（长芒麦和皇冠麦），已知这两个品种在当前环境条件下的 gm 存在差异：冰期（206 μmol mol-1）、前工业化（344 μmol mol-1）、当前环境（489 μmol mol-1）和超升高（1085 μmol mol-1），以及两种水分处理条件（充分供水和适度水分限制），以从进化和未来气候的角度研究 gm 对光合作用和水分利用效率（WUE）的控制。在这两个小麦品种中，gm 随着 [CO2] 从冰期到环境 [CO2] 的升高而增加，但在超升高 [CO2] 时下降。gm 对不同生长 [CO2] 的响应也取决于水分胁迫；然而，gm 对 [CO2] 的响应的具体机制仍不清楚。尽管 gm 和 gm/gsc（叶肉导度/气孔导度）与光合速率（A）和 WUE 的可变性密切相关，但我们发现具有较高 gm 的植物可以在不增加 gsc 的情况下增加 A，从而提高 WUE。这些结果可能有助于为澳大利亚小麦在未来环境条件下的植物育种计划和品种选择提供信息。
