Litter cellulolytic enzyme activities in alpine timberline ecotone of western Sichuan

Abstract

Aims Litter constitutes the major source of organic matter entering the soil. Different litter layers reflect different phases of decomposition. The litter originated from different plant materials and decomposition phases may have a significant impact on cellulolytic enzyme activities. Our objective was to explore the effects of vegetation types and decomposition phases on cellulolytic enzyme activities during litter decomposition process in an alpine timberline ecotone at the end of snow melting. Methods The activities of three cellulolytic enzymes(β-1,4-endoglucanase, β-1,4-exoglucanase and β-1,4- glucosidase) and litter qualities(C, N, P and cellulose content) were measured in the fresh litter and fermentation layer(LF) and the humus layer(H) in alpine meadow, alpine shrub, and coniferous forest in the alpine timberline ecotone in western Sichuan. Two-way ANOVA was used for testing the main effects of vegetation types, decomposition phase and their interactions on cellulolytic enzyme activities and litter qualities. We used Spearman correlations to explore the relationships between cellulolytic enzyme activities and litter qualities of two decomposition phases. Important findings Cellulolytic enzyme activities and cellulose contents in the LF layer were significantly higher than in the H layer across all vegetation types. Two-way ANOVA results showed that decomposition phase had a more significant impact on cellulolytic enzyme activities and cellulose contents than vegetation types. Cellulolytic enzyme activities were under the control of different factors between the two decomposition stages. In the early decomposition stage, the activities of β-1,4-exoglucanase and β-1,4-glucosidase appeared to be limited by N and P contents of the substrate, while β-1,4-endoglucanase activity was mainly controlled by the cellulose content of litter. In the late decomposition stage, the activities of β-1,4-endoglucanase and β-1,4-glucosidase were mainly limited by C and N contents. According to the prediction of ecological stoichiometry theory, microbial growth is considered to be nutrient-limited on substrates with C:N 27 or C:P 186. Overall, litter C:N and C:P were greater than 27 and 186, respectively, in the study area, indicating that cellulolytic enzyme activities werelimited by litter N and P contents. In particular, the microbial biomass was limited more significantly by N and P contents in the early decomposition stage in the alpine meadow, indicating that litter quality indirectly regulates cellulolytic enzyme activities of litter decomposition process in this alpine timberline ecotone.