Dynamics of invertase, xylanase and coupled quality indices of decomposing green and brown plant residues

In order to explore the relationship between changes in plant litter quality during decomposition at low and moderate temperatures and activity of enzymes involved in carbon cycling, we performed a litterbag experiment in the laboratory. ‘Brown’ and ‘green’ plant materials derived from Miscanthus×ogiformis Honda cv. Giganteus, Vicia villosa and Lolium multiflorum were placed in litterbags at 3 and 9 °C. During the 140-day incubation period, soil respiration was measured and the activities of xylanase and invertase were measured in the decomposing material. Also mass loss of water solubles, cellulose and lignin from the plant material were measured. As expected there were large differences in decomposition patterns between green and brown materials. Temperature effects on decomposition were much greater in the more resistant brown material. A double exponential decay model could be fitted to the respiration rates for the green materials, while respiration rates from the brown material were almost constant during the experiment, indicating different types of constraints on decomposition. This was confirmed from the mass loss of water solubles, cellulose and lignin. Enzyme activities in the decaying green materials were low during the first 10–18 d, where decomposition of low molecular substrates was predominant, but increased during the later stage. Thus, invertase was closely correlated with xylanase activity in the green materials, but not in the Miscanthus (brown material) treatment where the activities of both enzymes were initially rather high but decreased over time.