Seasonal Changes in Soil Biological and Hydrothermal Properties in a Rainfed Peach (Prunus persica Batch.) Orchard in Northwestern Himalaya, India

Season regulate soil biological and hydrothermal processes, yet their combined effects remain poorly understood. This study examined short-term variations in bacteria, fungi, and actinobacteria populations, basal soil respiration, dehydrogenase enzyme activity, total soil DNA, earthworm abundance, and soil hydrothermal properties across four seasons (spring, summer, monsoon, and winter) and six peach phenological stages (P–1: bloom; P–2: fruit setting; P–3: stone hardening; P–4: harvestable maturity; P–5: post-maturity; P–6: leaf shedding) under rainfed conditions in the Kumaon region of the northwestern Himalayas over two years (2016 and 2017). Soil of the study site is Mollisol and is micaceous, gravelly, shallow, well-drained, and loamy sand to sandy loam in texture. Surface (0–15 cm) and subsurface (16–30 cm) soils were sampled from a peach orchard and an adjacent perennial grassland (control). Bacteria and fungi populations increased significantly from early spring (P–1) to early summer (P–3), then declined until monsoon (P–5) for bacteria and late summer (P–4) for fungi, while actinobacteria counts decreased steadily from spring to monsoon. Peak abundances occurred in winter (bacteria), monsoon (fungi), and early spring (actinobacteria), highlighting the role of rhizodeposition in shaping microbial dynamics. Total soil DNA, basal respiration, and dehydrogenase activity increased sharply from spring to summer, declined during monsoon, and increased again in winter. Earthworm abundance was least affected by season or phenology but peaked in monsoon. Early summer (May) was the driest and warmest period across ecosystems. Short-term changes in soil biological and hydrothermal properties were best explained by season, likely linked to rapid shifts in plant growth, root exudation, and soil resources availability.