UC Irvine

Tropical montane cloud forests (TMCF) are defined by their characteristic cloud cover. This cloud cover endows these forests with unique structural and functional characteristics. However, climate change is reducing cloud cover, and causing warmer temperatures and longer dry periods in TMCF. Studies show that there will be devastating effects on plant and animal species aboveground. But, few studies have investigated soil communities and associated processes in TMCF. The goal of this dissertation was to characterize soil fungal communities and associated properties to determine how they respond to elevation. And in turn, assess how soil fungi and decomposition may respond to projected climate change.

In Chapter 1, I characterized soil fungal communities and associated properties along an elevation gradient in a TMCF in Monteverde, Costa Rica. I found that soil properties, fungal communities, and microbial processes varied with elevation and across seasons. In Chapter 2, I simulated the effects of climate change by performing a soil translocation experiment across this same gradient. I found that fungal decomposers and pathogens may increase under warmer, drier conditions. I also found that decomposition increased under these warmer, drier conditions. The results suggest that decomposition may increase, and plants and animals may be exposed to more pathogens. In Chapter 3, I compared canopy and ground soils along two elevation gradients. I also assessed if these two soil types differed in how their properties, fungal communities, and extracellular enzyme activity (EEA) varied with elevation. I found that fungal communities differed between canopy and ground soils. Moreover, canopy soils had greater EEA than ground soils, suggesting that canopy soils have a greater decomposition potential and may contribute greatly to C cycling. Carbon dynamics in canopy soil may also be particularly responsive to climate change even more than we might predict based on observations from ground soil. Collectively, the results of my dissertation provide insights into how the structure and function of TMCF may be altered through changes in the fungal community.