From active biomarkers to legacy effects: Linking microbial life strategies to carbon sequestration in alpine grassland restoration

Alpine grassland restoration is critical for soil organic carbon (SOC) sequestration, yet microbial mechanisms underlying SOC accumulation in moisture-heterogeneous ecosystems remain unclear. We investigated microbial-driven SOC dynamics along restoration chronosequence in arid and humid alpine grasslands through integrated biomarker analysis (amino sugars, glomalin-related soil proteins [GRSP], phospholipid fatty acids [PLFA], and enzymes). Results revealed distinct moisture-dependent carbon trajectories: linear SOC gain in arid grassland versus multiphase dynamics with SOC decline in humid grassland. Notably, amino sugars (arid: 5.4–7.7 %; humid: 3.0–6.9 %) were greater contributors to SOC than GRSP (<1.2 %). In arid grasslands, fungal necromass dominated SOC accrual driven by hydrolase and fungal proliferation, which evidenced by elevated fungal-to-bacterial (F/B) ratio and GluN/MurA ratios exceeding 13. Conversely, humid grasslands exhibited unimodal microbial succession, shifting from R- to r- and reverting to R-strategies, reflected in V-shaped F/B and gram-positive to gram-negative (GP/GN) ratios. Random forest and partial least squares path modeling analyses consistently identified moisture-driven SOC pathways: amino sugars strongly correlated with SOC in arid soils, with path coefficient ranging from 0.65 to 0.74, while GRSP dominated humid alpine systems (ranging from 0.47 to 1.37). We propose a dual-pathway SOC sequestration model: fungal necromass stabilization in arid alpine grassland versus bacterial-fungal-GRSP synergy optimizing nutrient cycling in humid soils. These findings advance the “microbial carbon pump” framework by integrating moisture-dependent necromass and GRSP dynamics, guiding climate adaptive restoration strategies for alpine grasslands.