Biomass and biochemistry: Litter impacts on community and ecosystem processes

Plants replace each other in space and time as dominant species in communities in part due to traits that affect their access to limiting resources. Decomposition is a critical link in nutrient cycling, determining the availability of nutrients for subsequent plant growth. Plant biochemistry interacts with site resources and climate to control microbial decomposer activity. I performed experiments designed to test the effects of litter biomass and biochemistry on plant community and litter decomposition dynamics. Manipulating litter levels resulted in litter-induced shading that changed plant communities in ways correlated with plant traits including seed size and functional grouping. Using ferns in Hawai'i, I focused on foliar biochemistry and resultant impacts on decomposition. Two groups of ferns, recently diversified monophyletic "polypod" ferns and all other "non-polypod" ferns had nutrient profiles distinct from each other and co-occurring angiosperms. Biochemical differences among these groups were preserved in litter and constrained decomposition rates; fern and angiosperm litter had distinct biochemical correlates of decomposition. Additionally, six common species were decomposed in a controlled low-nutrient environment. Analyses of microbial biomass, microbial community composition, and enzyme production demonstrated that initial litter lignin concentration controlled microbial colonization and litter decomposition. Litter carbon biochemistry did not change significantly until more than 50% of litter had disappeared. These results suggest that plant leaf characteristics that vary between functional and phylogenetic groups directly affect decomposition through changes in microbial dynamics, and litter production and decomposability are important structures of plant communities.