Enzymatic mechanisms of wood decomposition in tropical Australia

Steven Allison and Elizabeth S. Duan, Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA, Steven Allison, Earth System Science, University of California, Irvine, Irvine, CA, Habacuc Flores-Moreno, Biological Sciences, George Washington University, Washington, DC, Amy Zanne, Biological Sciences, The George Washington University, Washington, DC

Background/Question/Methods
Tropical forests store a significant fraction of Earth’s terrestrial organic carbon in aboveground biomass and soil. Still, wood dynamics in tropical forests remain uncertain, making it difficult to predict how tropical forest carbon pools will respond to climate change. Here we asked how key environmental drivers affect nine extracellular enzyme activities that contribute to wood decay along a rainfall gradient in tropical Australia. We established two common gardens to test how wood species, termites, and site conditions affected wood decomposition and enzyme kinetic parameters. A common garden in dry tropical savanna included logs from six native savannah species. The other common garden was located in lowland tropical rainforest and included logs from 10 native rainforest species. Termites were excluded from half the logs using mesh enclosures. Wood blocks were harvested after one year of incubation in the field. We hypothesized that the highest enzyme activities would occur in wood blocks with the most fungal decomposition, i.e. in the rainforest site and with termites excluded. Termite prevalence is greater in the savanna site, and we expected that termites might inhibit fungal decomposition.
Results/Conclusions
In contrast to our hypothesis, termite exclusion did not affect the potential activities of any enzyme at any site. We did, however, measure greater enzyme activities in the rainforest site as predicted. We also found that enzyme potentials varied significantly across wood species, suggesting that variation in wood traits affects fungal enzyme production and wood decay. Termite attack rates were low, suggesting that one year may not be long enough to observe significant impacts of termites on wood decay and enzymes. Overall, our results imply that wood traits and precipitation may be the dominant factors controlling deadwood turnover during the initial stages of decay in tropical Australia. This pattern may shift, especially in savanna, if termite attack rates increase during later stages of decay.