Minimum leaf conductance varied across 39 sub-tropical woody species with contrasting light requirement strategies

Minimum leaf conductance (gmin) refers to the residual water loss through plant leaf cuticle and incompletely closed stomata. Despite its importance in plant drought adaptation, the variation in gmin across forest trees and the factors influencing it remain poorly understood. In this study, we quantified the gmin of 39 tree species with contrasting light requirement strategies (light-demanding vs. shade-tolerant) in subtropical forests of southern China and analysed their correlations with leaf anatomical and physiological traits. We found that across the studied species, gmin was negatively correlated with cuticle thickness (R2=0.81), but positively correlated with the fraction of epidermis allocated to stomata (fgc; R2=0.17). Species with higher gmin tended to have greater fgc, which was associated with higher stomatal conductance (gs), elevated photosynthetic rates (A), and shorter leaf lifespans. Interestingly, compared with shade-tolerant species, light-demanding species displayed significantly higher gmin values, which might be attributed to their thinner cuticles and, to a lesser extent, greater fgc. Our results demonstrate that cuticle thickness is the primary driver of gmin variation in subtropical forest tree species. These findings reveal a tight linkage between gmin and leaf structure that is shaped by the contrasting light-requirement strategies of plants, thus highlighting the trade-off between carbon gain and dehydration tolerance at the leaf level.