Differential coordination of stomatal conductance, mesophyll conductance, and leaf hydraulic conductance in response to changing light across species

Stomatal conductance (g(s)) and mesophyll conductance (g(m)) represent major constraints to photosynthetic rate (A), and these traits are expected to coordinate with leaf hydraulic conductance (K-leaf) across species, under both steady-state and dynamic conditions. However, empirical information about their coordination is scarce. In this study, K-leaf, gas exchange, stomatal kinetics, and leaf anatomy in 10 species including ferns, gymnosperms, and angiosperms were investigated to elucidate the correlation of H2O and CO2 diffusion inside leaves under varying light conditions. Gas exchange, K-leaf, and anatomical traits varied widely across species. Under light-saturated conditions, the A, g(s), g(m), and K-leaf were strongly correlated across species. However, the response patterns of A, g(s), g(m), and K-leaf to varying light intensities were highly species dependent. Moreover, stomatal opening upon light exposure of dark-adapted leaves in the studied ferns and gymnosperms was generally faster than in the angiosperms; however, stomatal closing in light-adapted leaves after darkening was faster in angiosperms. The present results show that there is a large variability in the coordination of leaf hydraulic and gas exchange parameters across terrestrial plant species, as well as in their responses to changing light. In this paper, we explored the responses of gas exchange parameters and leaf hydraulic conductance to light changes in 10 species. In this study, we found (a) a phylogenetic trend emerges from ferns to angiosperms, consisting of increasing steady-state values for gas exchange and hydraulic capacities; (b) a similar phylogenetic trend is observed concerning the response of these parameters to varying light, with a gradual increase in the number of traits able to respond to light from none in ferns to all in angiosperms; (c) these phylogenetic trends may have exceptions, as illustrated here by the angiosperm species Centella asiatica, which behaves in all studied aspects similar to a fern; and finally, (d) differences among phylogenetic groups are also evidenced concerning in their stomatal kinetics, with stomatal opening faster in ferns and gymnosperms than angiosperms, but stomatal closing faster in angiosperms.