Cumulative cellulolytic enzyme activities and initial litter quality in prediction of cellulose degradation in an alpine meadow of the eastern Tibetan Plateau

Abstract

Abstract Aims Plant litter decomposition is a key ecosystem process that determines carbon and nutrient cycling in terrestrial ecosystems. As a main component of litter, cellulose is a vital energy source for the microbes associated with litter decomposition. The important role of cellulolytic enzymes in litter cellulose degradation is well understood, but seasonal patterns of cellulose degradation and whether cumulative enzyme activities and litter quality forecast cellulose degradation in an alpine meadow remain elusive, which limits our understanding of cellulose degradation in herbaceous plant litter. Methods A two-year field litterbag experiment involving three dominant species (Ajuga ovalifolia, Festuca wallichanica, and Pedicularis roylei) was conducted in an alpine meadow of the eastern Tibetan Plateau to explore the seasonal patterns of cellulose degradation and how cumulative cellulolytic enzyme activities and initial litter quality impact cellulose degradation. Important findings Our study demonstrates that cellulose degraded rapidly and exceeded 50% during the first year, which mainly occurred in the first growing season (31.9%–43.3%). At two years of decomposition, cellulose degradation was driven by cumulative endoglucanase (R2 = 0.70), cumulative cellobiohydrolase (R2 = 0.59) and cumulative 1,4-β-glucosidase (R2 = 0.57). In addition, the concentrations of cellulose, dissolved organic carbon, total phenol, lignin and lignin/N accounted for 52%–78% of the variation in cellulose degradation during the two years of decomposition. The best model for predicting cellulose degradation was the initial cellulose concentration (R2 = 0.78). The enzymatic efficiencies and the allocation of cellulolytic enzyme activities were different among species. The cellulolytic enzyme efficiencies were higher in the litter of F. wallichanica with relatively lower quality. For the complete cellulose degradation of the leaf litter, A. ovalifolia and F. wallichanica required 4-fold and 6.7-fold more endoglucanase activity, 3-fold and 4.5-fold more cellobiohydrolase activity and 1.2-fold and 1.4-fold more 1,4-β-glucosidase activity, respectively, than those required by P. roylei. Our results demonstrated that although microbial activity and litter quality both have significant impacts on cellulose degradation in an alpine meadow, using cellulose concentration to predict cellulose degradation is a good way to simplify the model of cellulose degradation and C cycling during litter decomposition.