Print PageLeaf litter decomposition by microbes is a principal carbon and energy cycling process. Studies investigating the influence of litter diversity on this process have produced conflicting results. We designed and conducted a leaf litter decomposition study to address these reported, conflicting results. Specifically, we examined: 1) the effect of litter diversity on decomposition rates and microbial extracellular enzyme activity, 2) the influence of individual leaf species within litter mixtures, and 3) whether decomposition rates would vary in upland vs. riparian forest habitats. We examined decomposition of four leaf species (Fagus grandifolia, Quercus palustris, Acer saccharum, and Hamamelis virginiana) in nine diversity treatments (4 single species, 4 mixtures of three species, and a four species mix) in two Northeast Ohio temperate forest habitats (upland and riparian). To determine the effect of individual species on diversity treatments, leaves of different species were separated during processing of mixed species bags. Bags were deployed in November 2007 and harvested at approximately 11 week intervals over the course of decomposition year. We quantified variables related to the microbial community (fungal & bacterial biomass, 7 extracellular enzyme assays, and community composition assessed via TRFLP), resource pools (leaf cellulose, lignin, non polar and polar extractives, C:N ratio, & proportion of C & N recovered) and decomposition (recovered AFDM).
Results/Conclusions There was a significant litter diversity treatment effect with mixed species bags having higher fungal and bacterial biomass than single species bags. However, diversity treatment did not significantly affect extracellular enzyme activity. Extracellular enzyme activity was significantly affected by leaf species regardless of which diversity treatment the leaves were in. This suggests that physiological traits (enzyme activity) responded to specific resource pools (individual leaf species), while community response (biomass) was stimulated by a mixed resource pool. Variables that were significantly affected by diversity treatment (lignin, cellulose, lignin/N ratio, and proportion of C and N recovered) point to the potential importance of nitrogen (N), as well as specific resource pools (lignin, cellulose) in regulating community biomass. Environmental influence on decomposition was evident with decomposition proceeding more rapidly in the upland than the riparian habitat. Initial results indicate that microbial community composition (T-RFLP profiles of 16S/18S rRNA genes) was predominantly related to differences between habitats. The results highlight the complex dynamics of leaf litter decomposition, including potential factors (physiology, biomass, decomposition rates) that may be influenced by individual leaf species, litter diversity treatments, and habitat.
