Functional Traits of Herbaceous Plants with Ecological Restoration Potential Under Drought Conditions

Herbaceous plant species form the plant synusia of desert ecosystems and play crucial roles in wind-breaking, sand-fixing, and the maintenance of oasis ecosystem stability. This study focused on the leguminous species <i>Medicago sativa</i> and <i>Astragalus laxmannii</i> and the gramineous species <i>Elymus dahuricus</i>, <i>Agropyron desertorum</i>, <i>Agropyron mongolicum</i> and <i>Agropyron cristatum</i>. These are the plants commonly used for ecological restoration in the desertification regions of northwestern China. We conducted a pot experiment with six soil moisture gradients (15% [ck], 12%, 10%, 8%, 6%, and 4%) to simulate drought conditions. We studied how varying degrees of drought stress influenced growth, functional traits and drought resistance, aiming to elucidate the mechanisms by which plants respond to drought. The study indicated that: (1) Drought stress directly and indirectly reduced both the seedling emergence rate and plant height. As soil water content decreased, the seedling emergence rate and plant height declined across all species. (2) The leaves and roots of the plants adopted different strategies to cope with drought stress. As soil water content decreased, leaf water content, leaf succulence, and leaf tissue density increased, while specific leaf area and leaf biomass decreased. Additionally, the root-shoot ratio increased, whereas root biomass, total root length, root surface area, and root volume all decreased. (3) Root system adaptation is the key factor influencing the drought resistance of plants. Drought resistance varied among the six species. <i>Medicago sativa</i>, <i>Elymus dahuricus</i>, and <i>Agropyron cristatum</i> exhibited stronger water retention and more stable growth under drought stress, making them better suited for ecological restoration in arid regions. Our study elucidates differentiation strategies for coping with drought stress and offers essential parameters and theoretical support for species selection and rational assemblage in the ecological restoration of arid regions.