Buttresses induced habitat heterogeneity increases nitrogen availability in tropical rainforests

Role of buttresses as a physical support to trees is well known, however, information on how buttresses form habitat heterogeneity and increase availability of nitrogen (N) in tropical rainforests is not yet much known. This study reports consequence of buttresses induced habitat heterogeneity on build up and supply of mineral N in a tropical rainforest of the South Andaman Islands of India. Treatment included buttresses (upslope) and adjacent (flat) microhabitats. Mineral N (NH4+N and NO3-N) and microbial biomass carbon (MB-C) pools and mineral N supply rate (net nitrification and net soil N mineralization rates) were measured in both microhabitats for consecutive 12 months representing wet, post wet and dry seasons. Buttress microhabitats accumulated 7 t ha−1 yr−1 litters, which was 62% higher than adjacent microhabitats. The buttress microhabitats also had 13% more fine soil particles than adjacent microhabitats. Soil organic carbon (SOC), total N, mineral N and MB-C were 18%, 52%, 38% and 34%, respectively higher in the buttress than adjacent microhabitat. However, C/N ratio was lower in the buttress (18) than adjacent microhabitat (23). Net nitrification as well as net soil N mineralization rate was 45% and 44%, respectively higher in the buttress than adjacent microhabitat. High amount of rainfall during wet season reduced the net nitrification rate and NO3-N pool, but increased NH4+N pool; these phenomena probably protected mineral N from leaching losses and enhanced the habitat heterogeneity further. Net nitrification rate, net soil N mineralization rate and MB-C were inversely correlated to the rainfall amount. However, net soil N mineralization rate was positively correlated to MB-C. These observations suggest that buttresses accelerate nitrogen cycling at microhabitat scale and form habitat heterogeneity on a landscape scale (forest floor), which forms pockets of mineral N reserves and simultaneously increases supply of plant available N in the tropical rainforests.

► Buttress microhabitats accumulate litter greater than adjacent microhabitat.
► Buttress microhabitats had more fine soil particles than adjacent microhabitats.
► Buttress microhabitats contain grater SOC and total N, but lower C/N ratio.
► Buttress microhabitats have pockets of mineral N reserves and simultaneously increase supply rate of plant available N in tropical rainforests.