Cell wall pectin reshapes leaf drought tolerance in dry forests.

Cellular and leaf structural traits influence the regulation of leaf water balance, which in turn impacts leaf gas exchange, plant productivity and drought tolerance. Yet, the role of cell wall composition, and especially that of components that render cell walls flexible-such as pectin-in leaf water relations remains elusive. Here, we investigate the linkages among 26 traits, including cell wall composition, anatomy, and drought tolerance (described by pressure-volume curves) across 69 woody species from sub-tropical dry and wet forests. We find that the lower wilting point of species of dry forests relative to wet forests is associated with contrasting anatomy and wall composition. Pressure-volume traits correlate more strongly with wall composition, and particularly pectin concentration, in dry forests, and with anatomy in wet forests. Thus, pectin-enriched cell walls contribute to the ecological specialization of woody plants in dry versus wet forests. Our findings indicate that leaf hydraulic designs diverge according to two strategies: dry forest species vary in elastic and osmotic function via contrasting pectin concentration ("flexible cell wall" strategy), whereas wet forest species do so via contrasting palisade tissue investment ("stable leaf tissue" strategy). Overall, diversity in cell wall properties across species are strongly linked with drought tolerance.