川西高山林线交错带凋落物纤维素分解酶活性研究

Litter cellulolytic enzyme activities in alpine timberline ecotone of western Sichuan

以川西高山林线交错带3种典型植被类型(针叶林、高山灌丛、高山草甸)下两个层次(LF层:新鲜凋落物层和发酵层;H层:腐殖质层)的凋落物为研究对象,分别模拟凋落物分解的前期和后期阶段,对凋落物分解过程中的纤维素酶活性及凋落物质量进行了研究。结果表明,凋落物分解前期的纤维素酶活性和纤维素含量均显著高于分解后期,但植被类型对LF和H层的纤维素含量的影响都不显著。双因素方差分析结果表明,凋落物分解阶段对纤维素酶活性和纤维素含量的影响比植被类型对纤维素酶活性和纤维素含量的影响更大。不同种类的纤维素酶活性在分解前期和分解后期受到不同因子的限制。凋落物分解前期,微晶纤维素酶和β-葡萄糖苷酶活性可能受N、P含量的限制,而羧甲基纤维素酶主要受底物纤维素含量控制;凋落物分解后期,羧甲基纤维素酶和β-葡萄糖苷酶可能受C、N含量的限制。生态化学计量学的理论预测,底物质量比C:N>27或C:P>186时会限制微生物生长,因此判断高山林线交错带凋落物微生物生物量和纤维素酶活性同时受到底物N、P的限制,尤其是高山草甸上微生物生物量在凋落物分解前期受到底物N、P的限制比分解后期更显著,这充分说明了底物质量调控着凋落物分解过程中的纤维素酶活性和微生物生物量。

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, decom- position phase and their interactions on cellulolytic enzyme activities and litter qualities. We used Spearman cor- relations to explore the relationships between cellulolytic enzyme activities and litter qualities of two decomposi- tion 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. Cel- lulolytic 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 were limited 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.