林下植被对马尾松人工林凋落物分解的影响

The process of material cycling by improving the litter decomposition is one of the critical management methods for the sustainable development of plantations. Reasonable understorey management might improve the litter decomposition process, however little information of which is available. Therefore, based on the scientific hypothesis that understory vegetation might change the properties of mixed litter composition and the micro-environment and then have effects on the litter decomposition process. In the present study, Pinus massoniana plantations in subtropical China, which will be controlled by the removal of woody species and herb species and both of them are removed, will be selected to evaluate the litter loss mass, nutrient release, the microbial biomass and the microbial community structure during the decomposition process. Natural mixed litter without any treatment will be selected as the control. Accordingly, combined with the simultaneous dynamic monitoring of temperature and humidity, the relationships between the quality change of mixed litter and the decomposition process will be analyzed. The present study will be conducive for revealing the effects of undertory vegetation in Pinus massoniana plantations on the litter decomposition process, which will provide scientific suggestions for the reasonable management of understory vegetation and the sustainable development of Pinus massoniana plantations.

改善凋落物分解为主要渠道的物质循环过程是单一树种人工林可持续经营的关键手段之一，合理的林下植被管理可能促进凋落物分解，但缺乏必要的关注。因此，基于“林下植被可改变地表混合凋落物特征及分解环境，改善凋落物分解过程”的科学假设，拟以亚热带典型成熟马尾松人工林为研究对象，基于前期对凋落物组分的认识，采用除灌、除草和同时去除灌草等措施，以原位条件下自然混合凋落物及其组成比例为对照，通过去除灌木凋落物、草本凋落物及灌草凋落物，研究凋落物分解过程中失重、元素释放以及微生物生物量与群落结构特征。结合同步温湿度环境因子动态监测，分析混合凋落物质量变化与分解过程的相互关系，揭示林下植被变化影响马尾松人工林凋落物分解的作用过程，为马尾松人工林林下植被的合理管理与可持续经营提供一定的理论依据。

合理的林下植被管理是改善人工林物质循环过程，实现可持续经营的关键手段之一，而林下凋落物组成特征、微环境响应及二者的交互作用是深入理解人工林系统以凋落物分解为主要渠道的养分归还过程的重要内容。本项目通过野外调查、野外固定样地实验以及分子生物学手段，对林下植被处理条件下凋落物的分解特征、非加合效应表现及微生物响应机制进行了分析，探讨了林下植被处理对系统凋落叶分解的影响。研究发现，（1）马尾松凋落叶基质质量较低，但其与柏木和栓皮栎等主要造林树种混交，能显著提升林分凋落叶的分解速率；与马尾松人工纯林相比，马尾松+栓皮栎混交林能显著增加1.2%的氮释放，马尾松+栓皮栎和马尾松+柏木+栓皮栎混交林分别能显著增加6.2%和3.5%的磷释放。（2）林下植被的去除显著影响了微环境要素：灌木去除样地和灌草层植被皆去除的样地其年平均温度能分别增加0.57°C和1.32°C，相同类型凋落叶的微生物量碳氮在不同处理样方中表现出随林下植被去除(除灌、除草)逐渐降低的趋势。（3）研究期内，39.92%到90.35%的质量损失以及5.9%到41.4%的初始木质素降解发生，林下植被显著增加了林地凋落叶二者的损失/降解率；林下植被的去除会降低凋落叶分解过程中的非加合效应表现，尤其是在灌木去除的样方中，且林下植被存在的样地能够表现出正向非加合效应（协同促进机制）；大部分时期实际分解环境的非加合效应与皆基于林下植被完全去除样地拟合的非加合效应特征有显著差异。（4）林下植被具备的样地，尤其具备林下灌木，草本次之，能够显著改善林地凋落叶碳氮磷释放、木质素纤维素降解、金属元素钾钙镁猛释放以及微生物生物量和群落结构，大部分时期提高其分解/降解率，丰富微生物群落组成。因此，通过研究表明，马尾松人工林改造等人为活动下的关键生态过程（凋落叶失重、元素释放、难降解物质降解及其非加合效应表现）受地表凋落物组成及微环境因子协同影响；林下植被维持（尤其灌木）具有促进人工林系统凋落物养分归还的功能。