Leaf shrinkability with dehydration: Coordination with hydraulic vulnerability and ecological implications

Background/Question/Methods

Leaf water transport affects the ability of leaves to maintain photosynthesis for well watered and droughted plants, and their growth. For over 100 years, leaf shrinkage with dehydration has drawn attention, especially as it can become extreme during drought, and potentially impact on the pathways of water transport, and their efficiency. Indeed, leaf thickness decreases during transpiration with declining water status and fluctuates daily and seasonally, corresponding to the loss of turgor in mesophyll and epidermal cells. Past studies have tended to focus on single species. We aimed to determine how species vary in shrinkability, and how leaf shrinkability may relate to the decline of leaf hydraulic conductance (K_leaf ), and thus to loss of leaf function during drought. We characterized leaf shrinkability in thickness and area across 14 species diverse in phylogeny, leaf traits and drought tolerance, toward insights into the mechanisms and hydraulic implications of leaf shrinkage. We measured mass, thickness and area as leaves dehydrated on the bench, and related  leaf shrinkage to  pressure-volume curve parameters, venation architecture and leaf hydraulic vulnerability.

Results/Conclusions

Species varied in their shrinkablity, with drought sensitive species showing substantial shrinkage in thickness and area above turgor loss point, whereas drought tolerant species experienced less shrinkage above turgor loss point, with moderate shrinkage below turgor loss point. We found no role of vein density in leaf shrinkage resistance, contrary to the long standing hypothesis that species with higher vein densities would provide more structure to the leaf and would by consequence experience less shrinkage. Rather, across species, shrinkage in thickness above turgor loss point was correlated with a low elastic modulus and higher osmotic potential at full turgor. Further, across species, K_leaf decline with mild dehydration (i.e., the initial slope of the vulnerability curve) was correlated with the degree of shrinkage above turgor loss point. These findings show for the first time a role for leaf shrinkability on hydraulic decline at high water potentials. These findings can impact processes across scales from the cell to the leaf function to ecological distributions.