Mechanisms underlying rhizosheath dynamics in Kengyilia hirsuta in response to alternating drought and rewatering

Under increasing extreme climate events, plants must adapt to alternating drought–rewatering stress. Kengyilia hirsuta , a pioneer forage grass in alpine desert regions, depends on its rhizosheath for drought resistance. This study simulated alternating and continuous drought–rewatering treatments (10%–40% field capacity) to investigate root architecture, biomass allocation, arbuscular mycorrhizal fungi (AMF) symbiosis, and rhizosheath formation. Results showed that rhizosheath accumulation responded dynamically to water regimes: continuous 25% moisture stress (W ₅ ) significantly promoted rhizosheath biomass, whereas 40% stress (W ₆ ) enhanced early-stage development and 10% rewatering (W ₁ ) boosted later-stage formation. AMF colonization increased progressively, with total colonization rising from 41.51% (T ₁ ) to 61.40% (T ₃ ). The W ₅ treatment consistently showed the highest vesicle, arbuscule, and hyphal colonization, alongside increased soil spore density and hyphal density by T3. Root morphological traits—including surface area, volume, tip number, hair length, and hair density—peaked under W ₅ . Structural equation modelling identified AMF colonization (total effect: − 0.90) and root hair traits (total effect: +0.80) as pivotal regulators of rhizosheath formation, interacting through biomass allocation, root architecture, and soil microenvironment to form a multidimensional adaptive network. These findings elucidate the ecophysiological mechanisms underlying plant–AMF collaboration in rhizosheath formation under water fluctuation, supporting selection of stress-tolerant grasses for restoring desertified grasslands.