Functional plant strategies mediate post-fire ash–precipitation effects on soil–vegetation feedbacks in a dry-valley forest ecosystem: implications for restoration

Wildfire fundamentally alters forest soil properties and vegetation dynamics through changes in ash deposition and post-fire precipitation, yet the coupled mechanisms governing soil–plant feedbacks remain unclear. We conducted a full-factorial pot experiment in the dry valleys of southwestern China, crossing four ash thicknesses with four precipitation levels and incorporating two contrasting plant functional types: the pioneer grass Digitaria sanguinalis ( L. ) Scop . and the drought-tolerant crop Fagopyrum tataricum ( L. ) Gaertn . We monitored soil respiration, near-surface soil moisture and temperature, and plant height throughout early growth. Structural equation modeling and response surface analysis revealed distinct regulatory mechanisms. D. sanguinalis exhibited a nutrient-driven, water-tolerant strategy in which ash and temperature dominated respiratory responses, supporting rapid growth under moderate ash layers. In contrast, F. tataricum followed an ash-facilitated, moisture-threshold strategy, where high ash combined with high precipitation suppressed respiration but maintained stable height. Across both species, a consistent negative association between respiration and plant height reflected a fundamental carbon allocation trade-off between metabolic expenditure and structural growth. Based on these findings, we propose a staged restoration model that leverages the contrasting functional strategies of pioneer and drought-tolerant species to accelerate ground cover formation and stabilize ecosystem functioning in fire-affected dry-valley forests. These results provide mechanistic insights and practical guidance for post-fire restoration and carbon management in fire-prone landscapes.