Year of Award

2011

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Resource Conservation

Department or School/College

College of Forestry and Conservation

Committee Chair

Cory Cleveland

Commitee Members

Anna Sala, Sasha Reed, Solomon Dobrowski

Keywords

extracellular soil phosphatase activity, nitrogen and phosphorus cycling, soil biogeochemistry, species diversity, tropics

Abstract

Tropical rain forests are known for their tremendous biological diversity, but the effects of plant diversity on important ecosystem processes remain unclear. Interspecies differences in both the demand for nutrients and in foliar nutrient concentrations could drive differences in litter chemistry that affect both pools and fluxes of belowground resources. Yet, our understanding of the effects of aboveground biogeochemical heterogeneity on belowground ecosystems is poor, especially in the species-rich forests of the wet tropics. To investigate the effects of tree species diversity on belowground biogeochemical processes, I examined how carbon (C), nitrogen (N), and phosphorus (P) cycles vary under canopy tree species – including legume and non-legume species – that vary in foliar leaf nutrient concentrations in a wet tropical forest in southwestern Costa Rica. I found significant differences in belowground C, N and P cycling under different canopy tree species. Total C, N and P pools in standing litter varied by species, as did total soil and microbial C and N pools. Rates of soil extracellular acid phosphatase activity (Ptase) varied both by species and functional group, with higher rates of Ptase activity observed under legumes. In addition, Ptase activity was significantly negatively correlated to litter N/P, suggesting a tight coupling between N and P cycles belowground. I also conducted a laboratory incubation experiment in attempt to isolate the effects of litter chemistry on belowground biogeochemistry. Results showed a significant relationship between litter chemistry and cumulative C mineralization and inorganic N availability, but litter chemistry did not affect soil labile P pools or Ptase activity. Overall, my results suggest the importance of aboveground plant community composition in promoting belowground biogeochemical heterogeneity at small spatial scales.

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© Copyright 2011 Adrienne Blair Keller