抚育择伐对马尾松林凋落叶分解速率和养分释放的短期影响

Short-Term Effects of Selective Cutting for Tending on Leaf Litter Decomposition Rate and Nutrient Release in Pinus massoniana Forests

【目的】探讨不同抚育择伐处理对马尾松林凋落叶分解速率和养分释放规律的短期影响,为马尾松生态公益林可持续经营提供科学依据。【方法】以三峡库区马尾松为研究对象,设置未择伐(保持林分现状,无人为干扰)、除灌(清除林内灌木层和阔叶更新层,保留马尾松更新小树)、伐除非马尾松(伐除胸径≥4 cm的非马尾松树种,择伐强度为15%)和伐除优势马尾松(伐除树木平均胸径以上的马尾松个体,择伐强度为70%)4种抚育择伐处理,采用原位分解法,分析不同抚育择伐处理下马尾松林凋落叶经历12个月后的分解速率和养分释放率差异,并探讨影响凋落叶分解的主要因素。【结果】未择伐、除灌、伐除非马尾松和伐除优势马尾松4种抚育择伐处理的凋落叶年分解速率分别为0.304、0.397、0.311和0.315 g·g-1a-1;相比未择伐,除灌、伐除非马尾松和伐除优势马尾松抚育择伐处理均可在一定程度上提高马尾松林凋落叶分解速率,分别提高30.59%、2.30%和3.62%;随着分解进程,不同抚育择伐处理下马尾松凋落叶C含量在前6个月显著降低,随后轻微波动,N含量呈先释放后持续固持的趋势,P含量则无规律性变化;处理与分解时间的交互作用对C和N释放速率影响显著,而对P影响不显著;凋落叶分解速率与初始N含量和N/P显著正相关(P<0.05),而与5 cm深处土壤温度和土壤水分含量相关性不显著(P>0.05)。【结论】短期来看,不同抚育择伐处理均能提高马尾松林凋落叶分解速率,减缓养分过度累积,促进养分归还土壤。未来开展马尾松林经营时,应选择林分各层次的轻中度择伐,以调控形成合理林分结构、促进马尾松林养分循环。

【Purpose】Understanding the rate of litter decomposition and the pattern of nutrient element release will help to detect the ecosystem function of nutrient cycling under different models of selective cutting and provide scientific basis for sustainable management for ecological public welfare forests.【Method】In the Three Gorges Reservoir area,one no-cutting treatment(retaining the forest state without any cutting)and three selective cutting treatments including shrubs cutting(removed the shrub and hard wood saplings except the regenerated Pinus massoniana saplings),non-P.massoniana cutting(removal of all DBH≥4 cm trees except P.massoniana,with a selective cutting intensity of 15%)and dominant P.massoniana cutting(removal of P.massoniana trees with the DBH bigger than the mean level,with a selective cutting intensity of 70%)were conducted in P.massoniana dominated forests.Decomposition in-situ method was used to study litter decomposition rate and nutrient release rate of P.massoniana leaves under four treatments and detect the dominant factors affecting the litter decomposition.【Result】The litter decomposition rate of P.massoniana was 0.304,0.397,0.311 and 0.315 g·g-1a-1 in no-cutting,shrubs cutting,non-P.massoniana cutting and dominant P.massoniana cutting stands respectively.Compared to the control of no-cutting,litter decomposition rate increased 30.59%under shrubs cutting,2.30%under non-P.massoniana cutting and 3.62%dominant P.massoniana cutting treatment.During the decomposition of leaf litter,a similar trend of nutrients release was observed under four selective cutting models.C concentration decreased significantly in the first 6 months and then slightly fluctuated,N concentration decreased at the initial decomposition stage and then continuously increased,while P concentration was constant and stable.Interaction of selective cutting measures and decomposition time had significant effect on the release rate of C and N,while had no significant effect on P concentration.The decomposition rates were positively correlated to the initial N concentration and N/P of the fallen leaves but not related to soil temperature or soil humidity.【Conclusion】In the short term,the decomposition rate of P.massoniana leaves was increased by all three selective cutting treatments compared to the no-cutting treatment.That means of selective cutting method can avoid nutrients to excessively accumulate in litter layer and promote them return into soil.In the future,selective cutting in slight or moderate degree will be a good way to build reasonable stand structure and facilitate nutrient cycling in coniferous plantation.