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.