Data from: Variable mesophyll conductance among soybean cultivars sets a tradeoff between photosynthesis and water-use-efficiency

Photosynthetic efficiency is a critical determinant of crop yield potential, though it remains below the theoretical optimum in modern crop varieties. Enhancing mesophyll conductance, i.e. the rate of carbon dioxide diffusion from substomatal cavities to the sites of carboxylation, may increase photosynthetic and water use efficiencies. To improve water-use-efficiency mesophyll conductance should be increased without concomitantly increasing stomatal conductance. Here we partition variance in mesophyll conductance to within and among cultivar components across soybeans grown under both controlled and field conditions, and examine the covariation of mesophyll conductance with photosynthetic rate, stomatal conductance, water-use-efficiency and leaf mass per area. We demonstrate that mesophyll conductance varies more than 2-fold and that 38% of this variation is due to cultivar identity. As expected mesophyll conductance is positively correlated with photosynthetic rates. However, a strong positive correlation between mesophyll and stomatal conductance among cultivars apparently impedes positive scaling between mesophyll conductance and water-use-efficiency in soybean. Contrary to expectations, photosynthetic rates and mesophyll conductance both increased with increasing leaf mass per area. The presence of genetic variation for mesophyll conductance suggests there is potential to increase photosynthesis and mesophyll conductance by selecting for greater leaf mass per area. Increasing water-use-efficiency though, is unlikely unless there is simultaneous stabilizing selection on stomatal conductance.

光合效率（Photosynthetic efficiency）是决定作物产量潜力的关键因素，但现代作物品种的光合效率仍低于理论最优水平。提升叶肉导度（mesophyll conductance，即二氧化碳从气孔下腔扩散至羧化位点的速率），可同时改善光合效率与水分利用效率。但若要提升水分利用效率，则需在增加叶肉导度的同时，不伴随气孔导度（stomatal conductance）的升高。本研究针对控制环境与田间条件下种植的大豆，将叶肉导度的方差分解为品种内与品种间组分，并分析了叶肉导度与光合速率、气孔导度、水分利用效率及比叶质量（leaf mass per area）之间的协变关系。研究表明，叶肉导度的变异幅度超过2倍，其中38%的变异源于品种差异。正如预期，叶肉导度与光合速率呈正相关。然而，不同品种间叶肉导度与气孔导度存在较强的正相关，这显然阻碍了大豆叶肉导度与水分利用效率之间的正向协同提升。与预期相悖的是，光合速率与叶肉导度均随比叶质量的增加而升高。叶肉导度存在遗传变异这一发现提示，通过选育更高比叶质量的品种，有望提升光合效率与叶肉导度。不过，除非同时对气孔导度实施稳定化选择，否则难以实现水分利用效率的提升。