Decay Rates, Nitrogen Fluxes, and Decomposer Communiies of Single‐ and Mixed‐Species Foliar Litter

Abstract

Decomposition rates, N fluxes, and abundances of decomposer organisms were quantified in mixed—species litterbags (containing leaves of two or three of the following tree species: Acer rubrum, Cornus florida, and Quercus prinus) and in litterbags containing leaves of a single species. Data from single—species litterbags were used to generate predicted decay rates, N fluxes, and abundances of decomposer organisms for mixed—species litterbags, against which observed values could be compared to determine if significant interaction effects occurred when litter of different species, and different resource quality, was mixed. Decay rates of mixed—species litterbags during the 1—yr study were not significantly different than predicted from decay rates of individual component species. However, there were significant interaction effects on N fluxes and abundances of decomposer organisms. In the C. florida—A. rubrum and C. florida—A. rubrum—Q. prinus litter combinations there were significantly greater initial releases of N and lower subsequent N immobilization than predicted. In the A. rubrum—Q. prinus and C. florida—A. rubrum—Q. prinus litter combinations, lengths of fungal hyphae were significantly less than predicted on at least half the collection dates. Bacterial numbers in the mixed—litter combinations were also generally less than predicted. Nematode abundances, especially fungivores, were generally greater than predicted in mixed—species litterbags until the last sample date. Observed mean abundances of nematodes over all dates were 20—30% greater than predicted. Microarthropod abundances were more variable, but tended to be lower than predicted. Our results indicate the measurement of N flux in single—species litterbags may not reflect actual N flux in the field, where leaves of several tree species are mixed together. The differences in N flux between single— and mixed—species litterbags can affect ecosystem—level estimates of N release or accumulation in decomposing litter. For example, estimates of ecosystem—level N fluxes at our field site, based on data from single—species litterbags, resulted in a 64% underestimate of N released by day 75 and a 183% overestimate of N accumulated in the litter by day 375, relative to estimates based on data from mixed—species litterbags. We suggest that the deviation of observed N fluxes in mixed—species litterbags from those predicted using single—species litterbags are the result of differences in the decomposer community, such as lower microbial and microarthropod densities and higher nematode densities, resulting when litter of varied resource quality is mixed together. Longer term studies will be needed to determine if the differences between observed and predicted decomposer communities in mixed—species litter combinations influence the latter stages of decomposition where invertebrate—microbial interactions may have a greater effect on decay rates and nutrient release.