Relation between water-use efficiency and nutrient availability in European semi-natural ecosystems

The CO2 and H2O exchange between plant ecosystem and the atmosphere is commonly interpreted in the terms of plant performance in response to micrometeorological conditions. Though changing light and weather conditions play a primary role in determining yearly ecosystem CO2 uptake and water loss, CO2 and H2O budgets are further modulated by nutrient availability (NA) and air deposition (AD). The influence of changes in NA and AD is observable only over longer time periods, thus when evaluating the time series of eddy covariance fluxes it is more practical to compare across different sites with contrasting levels of NA and AD. Water-use efficiency (WUE) proved to be a useful indicator of ecosystem performance and fitness and allows to evaluate changes in ecosystem functioning since it reflects the degree of stomatal regulation of carbon assimilation and water loss. In this contribution we will focus on the evaluation of NA of nitrogen, phosphorus, and calcium ions on WUE. For this purpose, we take advantage of the existing NA survey performed yearly within ecosystem stations belonging to the Integrated Carbon Observation System (ICOS) network. Nutrient concentrations are obtained from the leaf samples cut from sun-exposed part of the vegetation canopy. Though nutrient content in the soil is not available, leaf samples are expected to be a better measure as they should reflect both soil NA and nutrient accessibility to the plant. The wide selection of semi-natural ecosystems across Europe will allow to evaluate the capability of ICOS network to capture the impact of NA on WUE. Furthermore, we will evaluate how leaf NA relates with AD, especially in the case of nitrogen depositions. For this purpose, EMEP MSC-W modelled air deposition results will be used.