Leaf surface traits contributing to wettability, water interception and uptake of above-ground water sources in shrubs of Patagonian arid ecosystems.

BACKGROUND AND AIMS: The ecohydrological significance of leaf wetting due to atmospheric water in arid and semiarid ecosystems is not well understood. In these environments, the inputs of precipitation or dew formation resulting in leaf wetting have positive effects on plant functioning. However, its impact on plant water relations may depend on the degree of leaf surface wettability. In this study we evaluated leaf wettability and other leaf traits and its effects on foliar water uptake and canopy interception in plant species of a Patagonian steppe. We also studied how leaf traits affecting wettability vary seasonally from growing to dry season. METHODS: Contact angle of a water droplet with the leaf surface, water adhesion, droplet retention angle, stomatal density, cuticular conductance, canopy interception and maximum foliar water uptake were determined in six dominant shrub species. KEY RESULTS: All species increased leaf wettability during the dry season and most species were considered highly wettable. The leaf surface had very high capacity to store and retain water. We found a negative correlation between foliar water uptake and leaf hydrophilia. CONCLUSIONS: Despite the diversity of life forms, including cushion shrubs and tall shrubs, as well as phenological variability, all species converged in similar seasonal changes in leaf traits that favour wettability. Intercepted water by crowns and the extremely high capacity of retention of droplets on leaf surfaces can have a significant impact on eco-hydrological process in water limited ecosystems where most of water sources during the growing and the dry season may be small rainfall events or dew, which do not always increase soil water availability.

The impact of livestock grazing on the evapotranspiration-vegetation biomass relationship in a Southern Hemisphere salt marsh, Buenos Aires (Argentina).

Among the ecosystem services provided by salt marshes is the use of their natural vegetation as pastures for livestock production. As a result, the prediction of biomass productivity can be of great interest for the sustainable management of these environments. Evapotranspiration is one of the variables most used to estimate the yield of green biomass in pastures and crops, which to date has not been examined for natural environments such as salt marshes. We studied the aboveground biomass and species cover variability for two categories (erect and sward plants) in three plots affected by low, moderate, and high cattle grazing. Erect biomass was associated only with Spartina densiflora while for sward plants it gathered a diverse set of prostrate and stoloniferous species with high seasonal turnover. The evapotranspiration was estimated with a coupled surface resistance-Penman-Monteith model developed for these environments. The biomass of the plant categories shows different growth response according to livestock impact. S. densiflora has a slow-growing response after cattle consumption, even with high evapotranspiration. On the other hand, sward plants respond with biomass overproduction to livestock consumption, and a significantly positive relationship to evapotranspiration rate.