Density manipulation and pruning on fine root production and decomposition dynamics in a mature Acacia mangium Willd. stand in Kerala, India

Fine roots play a major role in water and mineral uptake and nutrient cycling in woody perennial-based ecosystems. Just as other biomass components, stand density manipulation and tree pruning may influence fine root production (FRP) and its decomposition dynamics. However, quantitative information on FRP and its turnover under different density and pruning regimes are meagre for most tropical trees. A field study was conducted to characterize FRP and associated nutrient release under varying stand density and pruning regimes in a 12-year-old Acacia mangium stand in Kerala, India. Soil ingrowth core method was employed for quantifying FRP and sequential core method for estimating standing fine root biomass. Annual FRP estimates were 5.78, 5.39, 3.74, and 3.38 Mg ha –1 for the 5000, 2500, 1250 and 625 trees ha −1 treatments, respectively. Allometric models based on tree diameter and basal area gave a good fit for annual FRP. Fine root turnover rates ranged from 2.81 to 3.16 yr −1 , which however, was not influenced by stand density. Carbon stocks ranged from 1.36 to 2.39 Mg ha −1 with highest FRP during rainy season and lowest during the dry period. The litterbag study using nylon mesh bags indicated that annual fine root mass loss ranged from 76.2 (5000 trees ha −1 ) to 96.8% (625 trees ha −1 ). Tree pruning had only modest effects on tree growth, FRP, and carbon and nutrient release patterns. The study highlights the importance of stand density manipulation in altering A. mangium FRP, soil carbon and mineral nutrient dynamics.