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

Abstract

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.