Florian Fort, Florence Volaire, Lydie Guilioni, Karim Barkaoui, Marie-Laure Navas, Catherine Roumet
In the context of a global increase in the frequency and intensity of droughts under climate change, root traits need to be explored to better understand their influence on water-use strategies of plants and communities. Perennial Mediterranean herbaceous species are an interesting model since they exhibit various spatial and temporal water-use strategies with contrasting adaptive responses to drought.
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. Each species was grown in monoculture in a common garden. Soil water content was monitored for ten months along the entire soil profile in each monoculture. These measurements were combined with climatic variables in a water balance model that assessed the amount and dynamics of water uptake of each species on a daily basis. Root morphological traits were measured at two soil depths (shallow and deep soil) and root biomass was measured along the soil profile to estimate species rooting depth.
We found that species with thin roots in shallow soil layers maximised water uptake in a short period following the peak of spring biomass production, while they used large amounts of water during periods of low water availability in summer. Conversely, species with coarse roots took up less water during the peak-growing season but maintained water uptake over a longer period of time and consumed less water during periods of low water availability. Deep roots with large diameters improved species’ ability to reach water from deep soil. Root biomass allocation in the deep soil layer was positively correlated to the amount of water consumed during periods of low water availability. Our results highlight that root traits influence spatial and temporal water-use among Mediterranean rangeland species. However, root traits account for the amount of water consumption during dry periods but not during the entire growing season.