The anatomical basis of leaf water relations across diverse species

Background/Question/Methods

The greatest challenge to terrestrial plant life is overcoming the relative moisture deficit. The resulting struggle between maximization of photosynthesis and costs of water transport has produced great diversity in plant anatomical and physiological traits. Consequently, understanding of plant water use and response to drought are of vital global importance.  Leaf physiological water use has been studied extensively, yet a disconnect remains in our understanding of the physiological processes which prevent transpiration and dehydration from creating lethal stress, and the diversity of anatomical structures within the leaf. For 14 phylogenetically and structurally diverse species growing in southern California, we quantified leaf cross sectional tissue thicknesses, cells sizes, and venation architecture. We hypothesized correlations with both maximum hydraulic capacity and drought tolerance traits.

Results/Conclusions

We found novel scaling relationships among anatomical traits, leaf composition and drought tolerance that have implications for leaf development, structure and environmental distributions. Across species, cell sizes were correlated across leaf tissues, including epidermis, spongy and palisade mesophyll and bundle sheath cells. Cell wall thickness tended to scale with cell size. Across species, thicker cell walls drove higher leaf mass per area and elastic modulus, and correlated with drought tolerance traits, including the ability to maintain leaf hydraulic conductance with dehydration and pressure volume curves. These findings suggest the importance of cell-level traits in leaf function and species' distriutions.