Ecological restoration in plateau pika-disturbed alpine meadows: Soil-microbe-enzyme stoichiometry and microbial adaptations during vegetation recovery of bare patches

Understanding the dynamics of soil-microbe-enzyme carbon (C) -nitrogen (N) -phosphorus (P) stoichiometry is essential for elucidating nutrient interactions and limitations that govern grassland restoration. However, its role during vegetation recovery of bare patches caused by plateau pikas (Ochotona curzoniae) remains unclear. This study applied a space-for-time substitution to classify bare patches into new, old, and abandoned stages, with vegetated patches as controls. Results demonstrated that as vegetation recovered, soil total N, enzyme C: N ratio, vector length, vector angle (always >45°), and threshold elemental ratios (TER)_{C: N} decreased (slope = -0.45, -38.8, -0.29, -1.06, and -6.64; p < 0.05), whereas soil C: N ratio, enzyme activities related to C-N-P cycles, and enzyme N: P ratio increased (slope = 1.15, 24.9, 1.23, 22.62, and 0.0008; p < 0.05). In contrast, soil organic C (SOC), soil total P (STP), and several stoichiometric ratios remained stable. This study further revealed the influence of relative environmental factors on stoichiometric patterns, identifying that SOC dominated the dynamics of soil C: N: P stoichiometry in early stage, STP and soil total potassium in intermediate stage, and pH and nitrate N in later stage. These findings indicate that N loss is the primary constraint at the soil level during vegetation recovery, while P supply remains relatively stable at the soil level but becomes limiting for microbes in later stages, persisting as the overarching limitation at the ecosystem level. Microorganisms maintain stoichiometric balance by adjusting metabolism and enhancing enzyme activities to optimize nutrient acquisition. To facilitate the sustainable restoration of bare patches caused by plateau pikas, targeted N supplementation through controlled-release fertilizers or N-fixing plants is recommended during early and intermediate recovery stages to alleviate N limitation, whereas the application of P fertilizers or P-solubilizing amendments may become important in later stages as microbial P demand increases.