底栖分解类群对金佛山森林溪流凋落物混合分解的影响

凋落物分解对于维持源头溪流生态系统碳和养分平衡有重要意义。以亚热带典型源头溪流金佛山溪流为代表，选取3种河岸带常见凋落叶为分解对象，设计3个单种和4个混合物种的凋落物组合，在原位放置3种孔径的分解袋（0.05mm、0.25mm和2mm），探讨混合凋落物的性状与底栖分解类群对叶片质量损失和混合效应的影响。结果表明：（1）微生物在凋落物分解过程中相对贡献均大于50%，小型和大型底栖动物进一步加速了凋落物的分解过程。（2）单种凋落物分解速率存在显著差异：八角枫（Alangium chinense，质量损失率为53.05%）>缺萼枫香（Liquidambar acalycina，30.00%）>薄叶润楠（Machilus leptophylla，12.63%）。（3）混合凋落物中仅微生物参与的处理均表现为负的非加和效应，其中八角枫+缺萼枫香、八角枫+薄叶润楠、八角枫+缺萼枫香+薄叶润楠三个处理的效应显著；小型底栖动物加入后均表现为正的非加和效应，但不显著；在微生物、小型和大型底栖动物的共同作用下，缺萼枫香+薄叶润楠和八角枫+缺萼枫香+薄叶润楠的两个处理的正的非加和效应显著。亚热带源头溪流中凋落物分解功能与河岸植物和分解者类群的复杂性密切相关。

Effects of benthic decomposers on the decomposition of litter mixtures in a forest headwater stream, Jinfo Mountain stream

The allochthonous input of detritus is the most important sources of energy in headwater streams. The decomposition of allochthonous organic matter as a fundamental ecosystem process for maintaining the balance of carbon and nutrient, is driven by a diverse array of benthic decomposers, but their contribution to the mixed litter decomposition is not well understood. In this study, we addressed the effects of the litter identity and benthic decomposers on the decomposition of litter mixtures in the Jinfo Mountain stream, a typical subtropical headwater stream in southwest China. We collected the three riparian plant species with different lignin to nitrogen ratios (Alangium chinense, Liquidambar acalycina and Machilus leptophylla) and designed seven combinations of the riparian plant species (i.e., three single species including, and four-mixed species). Then the litterbags of three mesh sizes (i.e., 0.05mm, 0.25mm, and 2mm) were chosen in the experiment to identify the effects of microbes, meiofauna and macrofauna. The results showed that:(1) microbes were the main contributor and their relative contribution of microbes in the litter decomposition process was greater than 50%; and both the meiofauna, and macrofauna further accelerated the litter decomposition process. (2) There were significant differences in the decomposition rates among single species:A.chinense (53.05% mass loss rate)>L.acalycina (30.00%)>M.leptophylla (12.63%). The higher quality (higher N and P content and lower C/N and C/P) of leaf litter, the faster decomposition process and the higher the microbial contribution; the lower quality of leaf litter, the slower decomposition process and the higher contribution of invertebrates. (3) For the mixed litter species, there was the significantly negative non-additive effect in the three treatments containing A. chinense (i.e., A. chinense+L. acalycina, A. chinense+M. leptophylla and A. chinense+L. acalycina+M. leptophylla, respectively) in the fine-mesh bags allowing the access of microbes. In the presence of microbes and meioinvertebrates, the non-additive effects of litter decomposition were positive but not significant. Moreover, in the coarse-mesh bags with the presence of microbes, meiofauna and macrofauna, the positive non-additive effects were significant in the two treatments (i.e., L. acalycina+M. leptophylla and A. chinense+ L. acalycina+M. leptophylla, respectively). When the number of mixed litter species increased, the complementation effect between species was enhanced, and the litter decomposition process was faster. In conclusion, the function of litter decomposition in the subtropical headwater streams is closely related to the identity of riparian plants and the complexity of decomposer groups.