BIOTROPICA 36(3): 285296 2004
Extracellular Enzyme Activities and Carbon Chemistry as Drivers of
Tropical Plant Litter Decomposition1
Steven D. Allison2
and Peter M. Vitousek
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, U.S.A.
Litter quality parameters such as nitrogen and lignin content correlate with decomposition rates at coarse scales, but fine-
scale mechanisms driving litter decomposition have proven more difficult to generalize. One potentially important driver
of decomposition is the activity of extracellular enzymes that catalyze the degradation of complex compounds present in
litter. To address the importance of this mechanism, we collected 15 Hawaiian plant litter types and decomposed them
in fertilized and control plots for up to two years. We measured litter nutrient content and carbon chemistry prior to
decomposition, as well as extracellular enzyme activities, mass loss, and litter nutrient content over time. We found that
water-soluble carbon content, cellobiohydrolase activities, and polyphenol oxidase activities were significantly correlated
with mass loss. Enzyme activities and decomposition rate constants both varied significantly by litter type, and fertilization
increased mass loss rates in five litter types. Some litter types that decayed faster under fertilization also showed time-
dependent increases in carbon-degrading enzyme activities, but others decayed faster independent of enzyme changes.
These results suggest that extracellular enzyme activities partially determine litter decomposition rates, but high soluble
carbon content may circumvent the requirement for enzyme-catalyzed decomposition.