ABSTRACT Grassland response to changes in water availability is closely tied to the traits of the plant community. Plants can adopt either moderate and efficient (conservative) or rapid and demanding (acquisitive) resource use strategies. These strategies combined with the plant interactions with microbes, such as arbuscular mycorrhiza fungi (AMF), determine the grassland productivity and efficiency. This study compares the drought response of two hay‐meadow seed mixtures commonly used in agricultural grassland that differ in their resource use strategies, representing conservative and acquisitive strategies. The mixtures were tested in 12 small‐scale lysimeters in an experimental garden under two irrigation levels (drought and wet). We measured water fluxes, aboveground and belowground phytomass and AMF spore productivity throughout a drought of 62 days. Despite differing resource use strategies, both mixtures exhibited similar reductions in actual evapotranspiration and aboveground phytomass under drought. However, the conservative mixture showed higher water use efficiency (WUE) when accounting only for aboveground phytomass and a less pronounced compositional shift. In the acquisitive mixture, the root:shoot ratio of grasses and the AMF spore abundance in the soil were reduced compared with the conservative mixture. We also identified legume productivity, roots and AMF spores' community composition as key factors influencing WUE. In a changing climate with greater frequency and severity of droughts in the European Alps, opting for grassland mixtures with more conservative characteristics should be considered, as they (i) reach the productivity of acquisitive grassland even under wetter conditions and (ii) show higher efficiency and delayed senescence under drought conditions.
Tello-García et al. (Mon,) studied this question.