Native Pseudomonas inoculants alleviate microbial resource limitations and enhance plant biomass in degraded alpine meadow soils.

Degradation of alpine meadow soils on the Qinghai-Tibetan Plateau disrupts carbon (C), nitrogen (N), and phosphorus (P) cycling, creating microbial resource limitations that constrain plant growth. Native microbial inoculants (MI) offer a low-environmental-impact alternative for restoring degraded soils. This three-year field study examined the effects of a native Pseudomonas inoculant (P. marginalis, P. silesiensis, P. antarctica, and P. putida) on soil nutrient status, microbial resource limitations (as assessed via extracellular enzyme stoichiometry), and plant biomass across a degradation gradient (non-degraded, ND; moderately degraded, MD; severely degraded, SD). MI application significantly alleviated microbial P limitation, reducing vector angle from >60° to <55°, but intensified microbial C limitation, increasing vector length from <1.2 to >1.4. MI consistently increased soil microbial biomass C (9.6-32.4%), N (4.6-36.1%), and P (3.1-22.0%), and enhanced C- and N-acquiring enzyme activities. These changes accompanied significant increases in aboveground (AGB) and belowground (BGB) biomass, with maximum increments of 20.1% and 37.5%, respectively. Path analysis revealed degradation-specific patterns: in MD soils, plant biomass was primarily associated with alleviation of microbial C limitation (path coefficient: 0.57); in SD soils, microbial biomass accumulation was a prerequisite for biomass restoration (path coefficient: 0.95). High-throughput 16S rRNA sequencing revealed that MI increased the copiotroph-to-oligotroph ratio from 1.21 to 2.08 in MD soils (p < 0.001) and from 0.78 to 1.55 in SD soils (p < 0.01). Microbial carbon use efficiency (CUE) decreased from 0.31 to 0.22 in MD soils (p < 0.001) and from 0.28 to 0.19 in SD soils (p < 0.001), and was negatively correlated with vector length (R2 = 0.502, p < 0.001). These findings indicate that native Pseudomonas inoculants are a practical management measure for degraded alpine meadows, with degradation-dependent efficacy that may inform restoration strategies in other cold, nutrient-limited grasslands.