Temporal changes in spatial pattern of fine-root mass and nutrient concentrations in Indian bamboo savanna

Abstract. Temporal variations in the spatial distribution of fine-root mass and nutrient concentrations were studied in recently harvested and mature bamboo savanna sites in the dry tropical Vindhyan region in India. The soil block method and root-free-soil cages were used to investigate fine-root dynamics. The mean annual fine-root biomass was 596 and 690 g/m² in harvested and mature sites, respectively. The fine-root net production calculated by different methods ranged from 486 to 749 g m^-2 yr^-1 in the harvested site and 485 to 875 g m^-2 yr¹ in the mature site. All fine-root mass fractions decreased with increase in distance from the base of bamboo clumps, and the herb root mass showed the reverse trend. Bamboo fine roots were better developed in the 10 - 20 cm soil depth and those of herbs in the upper 10 cm. The ingrowth of fine roots in root-free-soil cages showed maximum biomass accumulation during the rainy season (64.2 - 69.9 g m^-2 mo^-1) and minimum in the summer (4.5 - 7.5 g m^-2 mo^-1). The fine-root nutrient concentrations were strongly related to their diameter. The fine-root nutrient concentrations varied considerably in different seasons. The highest nutrient concentrations in all categories were recorded in summer followed by winter and rainy seasons. Nutrient concentrations in live roots were always greater than those found in dead roots in different diameter classes. We suggest the occurrence of nutrient retranslocation from senescent roots to surviving roots in bamboo savanna. Fine roots in the bamboo savanna increased as a function of N-mineralization and nitrification rates. This tendency further increased after the harvest of bamboo, suggesting the crucial role of fine roots in the bamboo savanna after the harvesting of bamboo culms.