UC Riverside

Disturbances, natural or anthropogenic, alter ecosystem functioning by changing the biotic composition, biogeochemical cycling, or the physical structure of an environment. As carbon dioxide is a major contributor to global climate change, disturbances to different components of the carbon (C) cycle may further affect atmospheric CO2 concentrations. Soils store vast amounts of C and have the potential to sequester or release CO2. Two of the most extreme ecosystems, deserts and tropical forests, play an important role in the global C cycle, storing C in soils and vegetative biomass. The overarching objective of this dissertation is to quantify changes in soil C cycling after a disturbance in desert and tropical ecosystems. My first chapter addressed how soil inorganic C cycling changes with vegetation removal in a Colorado desert ecosystem. Through manipulative field and lab experiments, I explored changes in C pools after vegetation removal by measuring changes in the isotopic composition of C pools and effluxed CO2. I found that there were significant changes in C cycling after the vegetation was removed; there were fewer newer C inputs and that a greater proportion of CO2 comes soil inorganic C in unvegetated soils. For my second chapter, I looked at soil C recovery with revegetation of Larrea tridentata, finding that there was some recovery of the water extractable organic and microbial biomass C pools. Although the isotopic composition of soil carbon pools did not change with restoration, I also found some seasonal patterns such that changes in soil C pools may have been linked to timing of shrub and microbial activity. My third chapter addressed spatial differences in root and hyphal dynamics and production associated with soil disturbances created by leaf cutter ants (LCA). I collected continuous soil data and automated minirhizotron images to assess belowground dynamics, finding that LCA altered their soil environment and increase root and hyphal production in LCA nests. Overall, my dissertation work demonstrates that disturbances impact various components of the C cycle and that changes to C cycling processes may change how relevant those processes are at different temporal and spatial scales.