Foliar water uptake in arid ecosystems: seasonal variability and ecophysiological consequences.

Abstract

Foliar water uptake (FWU) has been reported for different species across several ecosystems types. However, little attention has been given to arid ecosystems, where FWU during dew formation or small rain events could ameliorate water deficits. FWU and their effects on leaf water potential (ΨLeaf) were evaluated in grasses and shrubs exploring different soil water sources in a Patagonian steppe. Also, seasonal variability in FWU and the role of cell wall elasticity in determining the effects on ΨLeaf were assessed. Eleven small rain events (< 8mm) and 45days with dew formation were recorded during the study period. All species exhibited FWU after experimental wetting. There was a large variability in FWU across species, from 0.04mmolm-2 s-1 in species with deep roots to 0.75mmolm-2s-1 in species with shallow roots. Species-specific mean FWU rates were positively correlated with mean transpiration rates. The increase in ΨLeaf after leaf wetting varied between 0.65MPa and 1.67MPa across species and seasons. The effects of FWU on ΨLeaf were inversely correlated with cell wall elasticity. FWU integrated over both seasons varied between 28molm-2 in species with deep roots to 361molm-2 in species with shallow roots. Taking into account the percentage of coverage of each species, accumulated FWU represented 1.6% of the total annual transpiration of grasses and shrubs in this ecosystem. Despite this low FWU integrated over time compared to transpiration, wetting leaves surfaces can help to avoid larger water deficit during the dry season.