Soil microbial and enzyme activities in different land use systems of the Northwestern Himalayas

Soil microbial activity (SMA) is vital concerning carbon cycling, and its functioning is recognized as the primary factor in modifying soil carbon storage potential. The composition of the microbial community (MC) is significant in sustaining environmental services because the structure and activity of MC also influence nutrient turnover, distribution, and the breakdown rate of soil organic matter. SMA is an essential predictor of soil quality alterations, and microbiome responsiveness is imperative in addressing the escalating sustainability concerns in the Himalayan ecosystem. This study was conducted to evaluate the response of soil microbial and enzyme activities to land conversions in the Northwestern Himalayas (NWH), India. Soil samples were collected from five land use systems (LUSs), including forest, pasture, apple, saffron, and paddy-oilseed, up to a depth of 90 cm. The results revealed a significant difference (p < 0.05) in terms of dehydrogenase (9.97-11.83 TPF µg g^-1 day^-1), acid phosphatase (22.40-48.43 µg P-NP g^-1 h^-1), alkaline phosphatase (43.50-61.35 µg P-NP g^-1 h^-1), arylsulphatase (36.33-48.12 µg P-NP g^-1 h^-1), fluorescein diacetate hydrolase (12.18-21.59 µg g^-1 h^-1), bacterial count (67.67-123.33 CFU × 10⁶ g^-1), fungal count (19.33-67.00 CFU × 10⁵ g^-1), and actinomycetes count (12.00-42.33 CFU × 10⁴ g^-1), with the highest and lowest levels in forest soils and paddy-oilseed soils, respectively. Soil enzyme activities and microbial counts followed a pattern: forest > pasture > apple > saffron > paddy-oilseed at all three depths. Paddy-oilseed soils exhibited up to 35% lower enzyme activities than forest soils, implying that land conversion facilitates the depletion of microbiome diversity from surface soils. Additionally, reductions of 49.80% and 62.91% were observed in enzyme activity and microbial counts, respectively, with soil depth (from 0-30 to 60-90 cm). Moreover, the relationship analysis (principal component analysis and correlation) revealed a high and significant (p = 0.05) association between soil microbial and enzyme activities and physicochemical attributes. These results suggest that land conversions need to be restricted to prevent microbiome depletion, reduce the deterioration of natural resources, and ensure the sustainability of soil health.