Soil extracellular enzyme activities are sensitive indicators of detrital inputs and carbon availability

Abstract

In a litter manipulation experiment in a temperate deciduous oak forest in Central Europe, we examined soil carbon contents and density fractions, as well as β-glucosidase and polyphenol oxidase enzyme activities, which play central roles in the degradation of litter and soil organic matter. Our measurements were taken in the DIRT (detritus input and removal treatments) plots, where manipulations include doubling of leaf litter or woody debris inputs, as well as removal of litter, trenching to prevent root inputs, and removal of all litter inputs. After 10 years of manipulation, soil C content did not vary predictably among plots, although the amount of light fraction material was greater in control and litter addition plots compared to litter removal plots. Even after 10 years of litter addition, there were no significant differences in activities of either enzyme in double litter plots compared to control plots, a result consistent with other observed measures of microbial activity. However, removal of roots and litter caused significant decreases in β-glucosidase activities very quickly, and these differences increased over time. However, polyphenol oxidase activities were not significant different among treatments. Enzyme activities were not correlated with total soil carbon contents, but activities of both enzymes were significantly and positively related to the amount of light fraction carbon, suggesting that enzymes respond to increases in labile carbon availability.