Rhizosphere soil properties and microbial biomass changes with the chronosequence of stand age of broadleaf banj oak and coniferous deodar forests in the central Himalaya, India

Abstract

This research investigates the changes in rhizosphere soil (RS) properties in a chronosequence of the stand age of banj oak (Quercus leucotrichophora A. Campus) and deodar (Cedrus deodara D. Don) forests in the Kumaon Himalaya, India. Tree individuals of different girth classes (young, mature and old) were cored for tree age estimation using increment borer at breast height (1.37 m). Soil samples were collected in triplicate using a cubical section (15 × 15 × 15 cm) underneath the soil surface. Soil tightly adhered to the roots was brushed off on a paper bag and considered RS. Soil moisture content, pH, soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) were analyzed. Two-way ANOVA followed by Tukey's post-hoc was used to test the significant difference among the stand age and between species. SOC and MBC increased significantly (p < 0.05) from juvenile to mature and declined in old age, while TN and MBN decreased from juvenile to old age. SOC/TN ratios increased from juvenile to mature stand age, suggesting that plants require more nitrogen for canopy growth in mature stand age. PCA results reflected a strong coupling between juvenile age and MBN/TN ratio, confirming the higher accumulation of nitrogen in the living biomass of microbes. However, MBC/SOC and MBN/TN decreased with the stand age, reflecting that during the initial phase of growth, the microbial community requires more C and N for ecosystem functioning and development. MBC/MBN ratio increased from juvenile to mature stand age, indicating the nitrogen-poor litter quality in mature and old stand age. Overall, forest stand ages can significantly impact RS properties and microbial biomass. These changes can have important implications for ecosystem function and services such as nutrient cycling, water regulation, and carbon sequestration.