Drought Severity Shapes Recovery Trajectories of Root Functions and Rhizosphere Processes in Poa pratensis During a Drought–Rewatering Cycle

Drought–rewatering events are becoming increasingly frequent on the Qinghai–Tibet Plateau, yet how drought severity shapes post-drought recovery of root functions and associated rhizosphere enzyme activities remains unclear. Here, Poa pratensis from Zeku Zequ National Wetland Park was subjected to a control treatment (75–80% field capacity, FC), mild (60–65% FC), moderate (40–50% FC), or severe drought (30–35% FC) for 14 days, followed by 14 days of rewatering. Root functional traits, leaf physiological responses, chlorophyll-related traits, and rhizosphere soil enzyme activities were evaluated. Drought severity progressively impaired root function, chlorophyll-related traits, and rhizosphere enzyme activities, whereas moderate drought induced the strongest osmotic adjustment and antioxidant enzyme responses. After rewatering, most traits under mild drought approached control levels, moderate drought showed partial restoration, and severe drought retained substantial deficits in root function, water status, chlorophyll-related traits, and rhizosphere enzyme activities. Pearson correlation analysis and PCA further revealed coordinated variation among root functions, physiological status, and rhizosphere enzyme activities. These findings demonstrate that drought severity strongly influences post-drought restoration trajectories of root functions and rhizosphere processes.