Seasonal shifts in vegetation, soil properties, and microbial communities in Western Himalayan forests

The western Himalayan forest ecosystem faces escalating pressures from climate change and anthropogenic activities, demanding improved conservation strategies. Effective management requires understanding the seasonal fluctuations in vegetation, soil properties and microbial communities, but they remain poorly characterized across high altitude forests. We assessed these variables in 10 forest sites during the winter of 2023 and summer of 2024, analysing vegetation diversity, soil parameters, and microbial metagenomics.

We found pronounced seasonal shifts in plant and microbial diversities, and in soil properties. Plant species richness, and Shannon and Simpson diversity indices were higher (p < 0.001) in summer than in winter while the community maturity index was higher (p < 0.02) in winter than in summer. Soil properties exhibited clear seasonal patterns: pH, available phosphorus (AP), microbial biomass carbon (MBC) and cation exchange capacity (CEC) were higher (p < 0.05) in summer, whereas soil moisture (SM) and soil organic carbon (SOC) were higher (p < 0.05) in winter. Microbial alpha diversity indices (Shannon, Chao, and Sobs) were elevated (p < 0.05) in summer, while the Simpson index was elevated in winter, indicating a shift in community dominance. Beta diversity analyses revealed a significant seasonal shift in overall metabolic potential (KEGG orthologs; ANOSIM R = 0.222, p = 0.016), but not in general protein functions (COG), carbohydrate-active enzymes (CAZy), or taxonomic composition (RefSeq). Therefore, despite taxonomic turnover, core metabolic functions were maintained, indicating strong functional redundancy. Structural equation models (SEM) confirmed distinct seasonal dynamics, revealing stronger plant-soil-microbe interactions and a greater proportion of variance explained by the model in summer (R²=0.64-0.72 for key paths) than in winter (R²=0.52-0.63).

The findings demonstrate that the western Himalayan ecosystem undergoes a fundamental seasonal reorganization. Summer is characterized by increased biodiversity, distinct soil conditions, and more dynamic microbial-ecosystem interactions, while winter exhibits greater community maturity and functional stability. The resilience of core ecosystem processes is underpinned by microbial functional redundancy, which ensures metabolic continuity despite taxonomic shifts. We recommend that forest management strategies account for these seasonal dynamics and focus on preserving the conditions that support this critical functional redundancy.