Expensive and hydraulically efficient leaves maintain deep rooted cold desert shrubs active during the dry season

SCHOLZ FG, BUCCI SJ, EREYRA D, GOLDSTEIN G

Sacramento

Congreso; 99 Crongress of American Society of Ecology; 2014

Temporal and spatial variation in water availability is one of the main drivers of ecological diversity in arid ecosystems. Leaf hydraulic conductance (Kleaf) is a trait governing plant hydraulics, water use and gas exchange under water deficit conditions. As the transpiration stream in leaves occurs through vascular and extra-vascular tissues, a suite of morphological and anatomical traits implying substantial carbon investment can affect Kleaf. We investigated the relationships between Kleaf and drought resistance traits in shrub species of the Patagonian steppe and its functional relationship with leaf phenology.  Leaf hydraulic and water relations traits and leaf mass per area were determined in seven shrubs species ranging from deciduous and functionally deciduous species with more restricted soil water access than evergreen species tapping water from deeper soil layers. Results/Conclusions Evergreen species had access to more stable water sources; however their leaves exhibited traits related to drought tolerance compared to leaves from deciduous and functionally deciduous species with relatively shallow roots and lower soil water availability. Leaves from evergreen species had lower osmotic potentials and higher leaf mass per area, lower modulus of elasticity, solute content, and hydraulic capacitance but higher Kleaf both on area and mass basis and stomatal conductance than species exposed to larger water deficits. The strong and positive relationships observed between LMA and Kleaf on both an area and mass basis suggests that leaf water use and hydraulic efficiency are not optimized in species that maximize carbon gain possibly because they are uncoupled from seasonal changes in soil water availability by exploring deeper and wetter soil layers. However the construction of leaves with long lifespan (evergreen species) with high resistance to hydraulic failure and turgor loss, and the production of roots achieving deeper soil water sources implies a large energy cost with negative consequences on carbon gain at whole-plant level as photo-assimilates are allocated to roots, to active osmotically compounds and probably to a higher density of leaf vasculature.