不同营林措施对马尾松细根分解与养分释放的影响

Effects of different forest management practices on fine root decomposition and nutrient release in Pinus massoniana forests

细根(直径≤2 mm)是森林生态系统重要的碳库之一,其寿命短、代谢活性高,对外界环境变化十分敏感.了解不同营林措施对细根分解和养分释放的影响,对于合理开展森林经营管理具有重要意义.以三峡库区马尾松(Pinus massoniana)飞播林为对象,设置未择伐(NC)、除灌(SC)、伐除非马尾松(NPMC)和伐除优势马尾松(DPMC)等营林措施,在处理3年后,利用分解袋法研究不同营林措施对相同初始基质质量的马尾松细根分解和养分释放的影响.经过1年的分解,不同营林措施明显改变了土壤温湿度、土壤养分以及土壤微生物量碳氮,而对马尾松细根分解速率的影响不显著(P>0.05),细根分解速率与各环境因子间均无显著相关性.在分解过程中,各营林措施的细根C残留率逐渐降低,表现为DPMC>SC>NC>NPMC.N呈现先逐渐累积后释放的状态,P呈现释放-累积-释放的状态,且抚育择伐显著降低了P释放速率.短期来看,不同营林措施造成的林内环境因素变化不足以成为影响马尾松细根分解的主导因素,细根初始基质质量仍是影响细根分解的决定性因素.抚育择伐提高了细根C释放速率,降低了N和P元素的释放速率.

As a vital carbon sink in forest ecosystems, fine roots (≤2 mm in diameter) with short life span and high metabolic activity are sensitive to environmental changes. It is important to understand the mechanisms of fine root decomposition and nutrient release in response to forest management practices. To examine the effects of forest management on fine root decomposition, we employed three selective cutting managements, including shrub cutting (SC), non Pinus massoniana cutting (NPMC) and dominant P. massoniana cutting (DPMC), and a control with no cutting (NC) in P. massoniana plantation in the Three Gorges Reservoir area in 2013. After three years of forest management, litterbags filled with P. massoniana fine roots were buried in soil under different treatments. Mass losses and nutrient concentrations of fine roots were mea sured every three months. After one year decomposition, forest managements had significant effects on soil temperature and humidity, soil nutrients and soil microbial biomass carbon and nitrogen, but had no significant effect on the fine root decomposition rate. There were no significant correlations between fine root decomposition rate and environmental factors. During decomposition, C residual rates gradually decreased, showing a pattern of DPMC>SC>NC>NPMC. Nitrogen was immobilized first and then released, while P followed a mode of release immobilization release. The release rate of P was significantly reduced by selective cutting management. In all, the changes of environmental factors caused by forest management practices are not the dominant factors driving fine root decomposition of P. massoniana. The quality of fine root initial matrix is the decisive factor. Selective cutting management can increase C release but decrease N and P release rate.