Dynamics of soil bio-physicochemical properties under different disturbance regimes in sal forests in western Himalaya, India

Abstract

Disturbance is a key factor in controlling vegetation diversity, nutrient influx rate, and biochemical cycling in terrestrial forest ecosystems. Limited studies are available on changes in tree diversity, soil nutrients and enzyme activities in response to different intensities of land disturbances in the Himalayan forests. Present study investigated the impact of varying intensities of disturbances on tree diversity and their relationship with soil physical and bio-chemical properties in sal forests, Western Himalayas. Sites were categorized into four different classes of disturbances, namely, No disturbance (ND), Low disturbance (LD), Moderate disturbance (MD), and High disturbance (HD). Composite samples were collected at two depths (0-15 and 15-30 cm) in each plot to investigate soil physical and biochemical properties. Multivariate analyses were conducted to find relationship between tree vegetation and soil physical and biochemical properties. Soil organic carbon (C_org), total nitrogen (N_ttl), available phosphorous (P_avl), microbial biomass carbon (C_mic), nitrogen (N_mic), phosphorous (P_mic), and enzymes (dehydrogenase (DHA), Urease, acid and alkaline phosphatase) followed the order: MD > ND > LD > HD. Across disturbances, soil physical and biochemical characteristics significantly (p < 0.05) decreased with increasing soil depths. Across the sites, positive correlation was observed among soil microbial biomass, enzymes, C_org, clay, and moisture. Redundancy analysis (RDA) results revealed that species distribution is essential regulator in the variation of prominent soil variables, viz., nutrients (N_ttl and P_avl), C_mic, and DHA across disturbance categories and soil depths. Moreover, variance partitioning analysis (VPA) showed that changes in vegetation composition across disturbance levels explain 13.12 % of the variation in soil biochemical subset higher than soil physicochemical subset. The result illustrated that moderate disturbance increases species composition, soil nutrient properties and microbial activity. These findings would help understand microbial activity and its relationship with disturbances, suggesting site-specific measurements for soil nutrient availability and above-below ground interactions.

Keywords: Intermediate disturbance; Microbial biomass; Plant soil interaction; Soil enzymes; Soil nutrients.