FINE ROOT DYNAMICS AND PRODUCTION IN Acacia auriculiformis PLANTATION

Fine roots absorb water and nutrients for the tree's life and play an important role in carbon and nutrient cycling. Therefore, understanding fine root dynamics and production will contribute to sustainable management and improve the productivity of forest plantation. This work aims at investigating vertical distribution and production of Acacia auriculiformis plantation in Northeast Vietnam. A 20 m × 15 m plot containing 30 trees was established at a 2-year old plantation of A. auriculiformis. Sequence soil core sampling was applied to collect data on the mass of live roots and that of dead roots. While litter bag technique was used to estimate the decomposition ratio of dead fine roots. The continuous inflow method was employed to estimate fine root decomposition, mortality, and production. The results indicated that more than 50% fine roots distribute at 0-10 cm soil depth, while less than 12% distribute at deeper than 40 cm soil depth. In addition, more fine roots distribute at 0-10 cm soil depth in summer than that in winter. While more fine roots distribute at 40-80 cm soil depth in winter than that in summer. Fine root decomposition, mortality, and production are seasonal-dependent. The highest mortality (1.9 g m-2 day-1) was found during Dec-Mar and the lowest (1.3 g m-2 day-1) was found during Mar-Jun. While the highest mortality (1.8 g m-2 day-1) was found during Jun-Sep and the lowest (1.3 g m-2 day-1) was found during Sep-Dec. The similar pattern with mortality was found in production with the highest of 2.2 g m-2 day-1 during Jun-Sep and the lowest (1.2 g m-2 day-1) during Sep-Dec. In the present study plantation, total decomposition was 530 g m-2 year-1, mortality was 547 g m-2 year-1, and production was 548 g m-2 year-1. High production during Jun-Sep/summer may indicate a higher nutrient requirement to support growths during the growing season. Therefore, this should be a time for fertilizing plantation.