Understanding spatial heterogeneity in soil carbon and nitrogen cycling in regenerating tropical dry forests

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Bonnie Grace Waring1, Jennifer S Powers2, Sara Branco3, Rachel Adams3 and Erik Schilling1, (1)University of Minnesota Twin Cities, Minneapolis, MN, United States, (2)University of Minnesota Twin Cities, Department of Ecology, Evolution and Behavior, Minneapolis, MN, United States, (3)University of California Berkeley, Berkeley, CA, United States
Tropical dry forests (TDFs) currently store significant amounts of carbon in their biomass and soils, but these highly seasonal ecosystems may be uniquely sensitive to altered climates. The ability to quantitatively predict C cycling in TDFs under global change is constrained by tremendous spatial heterogeneity in soil parent material, land-use history, and plant community composition. To explore this variation, we examined soil carbon and nitrogen dynamics in 18 permanent plots spanning orthogonal gradients of stand age and soil fertility. Soil C and N pools, microbial biomass, and microbial extracellular enzyme activities were most variable at small (m2) spatial scales. However, the ratio of organic vs. inorganic N cycling was consistently higher in forest stands dominated by slow-growing, evergreen trees that associate with ectomycorrhizal fungi. Similarly, although bulk litter stocks and turnover rates varied greatly among plots, litter decomposition tended to be slower in ectomycorrhizae-dominated stands. Soil N cycling tended to be more conservative in older plots, although the relationship between stand age and element cycling was weak. Our results emphasize that microscale processes, particularly interactions between mycorrhizal fungi and free-living decomposers, are important controls on ecosystem-scale element cycling.