Fine root decomposition and nutrient mineralization patterns in a subtropical humid forest following tree cutting

Decomposition dynamics of fine roots (< 2 mm in diameter) and N and P mineralization pattern were studied in forest regrowths of three different ages in a humid subtropical region of India. The roots decomposed in a three-phased manner. The initial slow rate of decay up to 60 days was followed by a period of rapid weight loss until 120 days and then again by a phase of slow decay rate in all the three forest regrowths. A composite linear regression equation showed a good fit for the observed decay pattern of fine roots. The annual dry matter decay constants ( k) for fine roots (1.62–1.74) increased with the increase in the regrowth age. The mean daily weight loss was positively correlated with rainfall, air temperature, soil moisture and soil pH, and negatively correlated with initial lignin concentration. Nutrient release from decaying fine roots was influenced by seasonal cycle of mineralization and immobilization processes. Winter was the period of active N and P immobilization, while mineralization was rapid during rainy season when N and P concentrations in the decomposing fine roots recorded 45.5–57.6% decrease from the preceding season. The net annual mineralization of N decreased from 50.9% in the 7-year-old regrowth to 46.4% in the 16-year-old regrowth, while P showed a reverse trend by registering an increase from 37.3 to 51.4%.