Root growth dynamics during recovery of tropical mountain forest in North-east India

Abstract

Ever increasing pressures on tropical forests worldwide due to anthropogenic disturbances have greatly affected both above- and belowground functioning of these forests. While fine roots play major ecological roles in forests through assisting in nutrient and water uptake and returning elements to the soil environment, coarse roots play an important role in C sequestration. We studied changes in fine and coarse root biomass, production, turnover and carbon and nitrogen return to the soil in two regenerating forest stands (RFs) following stone-mining that were 5 years (RF-5) and 15 years (RF-15) post-disturbance compared with a natural forest stand (NF) in Mizoram, North-east India. Fine (§2 mm) and coarse root (2-10 mm) biomass differed significantly among the forest stands and ranged from 239 (RF-5) to 415 (NF) and 230 (RF-5) to 436 (NF) g m−2, respectively. Total root (fine + coarse) biomass increased during stand development but the proportion of very fine root (<0.5 mm) to total root production decreased. Fine root biomass decreased with increasing soil depth. Fine and total root biomass showed strong seasonal correlations with soil moisture, more so than for rainfall and temperature, whereas these relationships were less clear for the coarse root biomass. The amount of N (25–55 kg ha−1) and C (1.9–3.6 t ha−1) stored in root biomass increased with stand age with a corresponding increase in production and turnover of C and N to the soil. Disturbance to these tropical forests negatively affected root dynamics, influenced their spatio-temporal patterns, and reduced the production, amount and availability of nutrients returned to the soil along with a strong reduction in the root biomass carbon pool and sequestration in carbon residence time. We observed that root growth, especially fine roots, is dependent on abiotic variables, and plays a significant role in early stages of secondary succession by adding organic matter and nutrients through high turnover rates in these forests.