Coping with drought: root trait variability within the perennial grass Dactylis glomerata captures a trade-off between dehydration avoidance and dehydration tolerance

Abstract

Understanding plant adaptation to drought is a crucial challenge under climate change. This study aimed to investigate root traits and water use of grass populations exhibiting a range of dehydration avoidance and tolerance strategies to cope with drought. Sixteen populations of the perennial grass Dactylis glomerata originating from three biogeographical origins (Northern, Temperate and Mediterranean) were grown in long tubes. Plant biomass, rooting depth and morphological traits of deep roots were measured both under full irrigation and under severe drought. Water uptake under drought was used as a proxy for dehydration avoidance. Plant survival after severe drought was used as a measure of dehydration tolerance. All populations had similar maximum rooting depth and specific root length. Compared to Northern and Temperate populations, Mediterranean populations had half the total and deep root biomass, but thinner and denser deep roots. They were less affected by drought. These traits were associated with less water uptake (lower dehydration avoidance) but greater survival to severe drought (enhanced dehydration tolerance). The intraspecific variability in root traits revealed a trade-off between dehydration avoidance and dehydration tolerance which illustrates contrasting adaptive plant and root strategies associated with the biogeographical origins of populations.