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Substrate quality, nutrient availability, and enzymatic controls over litter decomposition rates.
ALLISON, S.1, FARRINGTON, H.1, VITOUSEK, P.1, 1
ABSTRACT- Litter inputs have the potential to affect nutrient dynamics in terrestrial ecosystems through litter quality characteristics, such as litter C:N, C:P, and lignin content. Changes in soil nutrient availability may in turn affect litter quality or decay rates. We studied litter decomposition dynamics in a lowland tropical wet forest site on the island of Hawaii and tested the hypothesis that high nutrient availability increases litter decomposition rates. Litter mass loss, N content, and P content were measured over time in fertilized (N-P-cations, 50-100 kg ha-1 yr-1) or unfertilized plots containing 15 litter types from native and exotic understory plants. To establish a biochemical basis for differences in mass loss and nutrient dynamics, we measured phosphatase, N-acetylglucosaminidase, cellobiohydrolase, and polyphenol oxidase activities in the decomposing litter. Litter decay rates varied from 1.0 yr-1 to 0.2 yr-1 and were significantly correlated with lignin:N and all enzyme activities. Fertilization had no effect on the decomposition rates of nutrient rich litter, but slowed recalcitrant litter decomposition. Litter always released P, but immobilized N before releasing it later in decomposition. Fertilization suppressed the activity of phosphatase and N-acetylglucosaminidase in recalcitrant litter, but stimulated activities in high nutrient litter types. Polyphenol oxidase and cellobiohydrolase activities did not respond strongly to fertilization. These results indicate that litter quality and nutrient availability interact to determine decay rates through the activity of degradative enzymes.
KEY WORDS: decomposition, litter quality, enzyme activity, nutrient dynamics