Root traits are related to plant water-use among rangeland Mediterranean species

Understanding the water-use of plants is timely under increasing drought stress due to climate change. Despite the crucial role of roots in water uptake, relationships between water-use and root traits are seldom considered. Combining a functional trait-based approach with a water balance model, we tested whether root functional traits are related to spatial and temporal water-use among 12 Mediterranean rangeland species grown in common garden monocultures. Soil water content was monitored for 10 months, and the dynamics of water uptake of each species was modelled at a daily time step. Root functional traits were measured at two soil depths (shallow and deep soil). Species with fast resource acquisition strategies in shallow soil, i.e. thin roots, maximised water uptake in a short period and consumed large amounts of water during periods of low water availability. Conversely, species with a more conservative root strategy, i.e. coarse roots, took up less water during the peak-growing season, maintained water uptake over a longer period of time and consumed less water during periods of low water availability. Deep root traits are strongly related to species' ability to take up water from deep soil. Deep roots with large diameters and low specific root length improve species' ability to reach water from deep soil. Biomass investment in the deep soil layer was positively related to the amount of water consumed during periods of low water availability. Our results highlight that root functional traits influence a range of spatial and temporal water-use among Mediterranean rangeland species. They account for the amount of water taken up during dry periods but not during the entire growing season. (Résumé d'auteur)