亚热带低山丘陵次生阔叶林米槠粗木质残体的短期分解速率与养分释放规律

Short-term decomposition rate and nutrient release of coarse woody debris in secondary broad-leaved forest in subtropical low mountain and hilly forests

【目的】探明不同分解等级下亚热带低山丘陵次生阔叶林内粗木质残体(coarse woody debris,CWD)的短期分解规律,为深入理解全球变化背景下亚热带森林生态系统的CWD分解机制及碳循环研究提供基础数据。【方法】以亚热带低山丘陵福建泰宁猫儿山国家森林公园次生阔叶林优势种米槠为对象,采用Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ5级分解等级对粗木质残体进行分等定级,同时测定林下不同分解等级CWD的分解速率和养分含量。【结果】CWD分解1 a后的质量残留率大小排序为:Ⅴ(69.10%)>Ⅳ(58.30%)>Ⅱ(56.68%)>Ⅰ(45.22%)>Ⅲ(31.06%);CWD分解速率均符合单因指数模型,k值大小排序为:Ⅲ(1.215)>Ⅰ(0.871)>Ⅱ(0.592)>Ⅳ(0.489)>Ⅴ(0.348),分解等级Ⅲ的分解速率显著高于其他等级(P<0.05);5种分解等级的CWD分解95%需要的时间排序为:Ⅴ(8.609 a)>Ⅳ(6.127 a)>Ⅱ(5.061 a)>Ⅰ(3.440 a)>Ⅲ(2.466 a)。分解1 a的过程中,CWD的全碳(total carbon,TC)、Mg含量逐渐降低,全氮(total nitrogen,TN)、全磷(total phosphorus,TP)、全钾(total potassium,TK)含量先下降后升高,Ca含量先升高后下降;分解1 a后,5个分解等级的CWD的TC残留率均在50%左右,等级Ⅰ、Ⅱ、Ⅲ的Mg残留率在30%左右,TC和Mg均表现为净释放;除等级Ⅰ、Ⅲ的TP表现为净释放外,等级Ⅴ的TN、TP、TK和Ca均表现为净累积。【结论】虽然存在元素的净释放,但是由于TC和其他主要元素的释放速率较慢,因而次生阔叶林粗木质残体是森林中重要的C库和长期的元素来源。

【Objective】To study the short-term decomposition laws of coarse woody debris(CWD)in subtropical low mountain and hilly secondary broad-leaved forests under different decomposition levels,it can provide a deep understanding of the CWD decomposition mechanism and carbon in the subtropical forest ecosystem under the background of global change.【Method】The secondary broad-leaved forest in the Maoershan National Forest Park,Taining,Fujian Province,was chosen as the research site.The coarse woody debris were classified into five decomposition levels,and the decomposition rate and nutrient content of CWD with different decomposition levels under the forest were measured.【Result】The mass residue rate after one year of CWD decomposition is sorted by size:Ⅴ(69.10%)>Ⅳ(58.30%)>Ⅱ(56.68%)>Ⅰ(45.22%)>Ⅲ(31.06%).The decomposition rate of CWD follows the single-factor exponential model,and the order of the k values is as follows:Ⅲ(1.215)>Ⅰ(0.871)>Ⅱ(0.592)>Ⅳ(0.489)>Ⅴ(0.348).The decomposition rate of decomposition levelⅢis significantly higher than other classes(P<0.05),and the time required to decompose 95%of CWD for the five decomposition classes isⅤ(8.609 a)>Ⅳ(6.127a)>Ⅱ(5.061 a)>Ⅰ(3.440 a)>Ⅲ(2.466 a).During the one-year decomposition process,the TC and Mg content of CWD gradually decreased,and the TN,TP,and TK content first decreased and then increased,the Ca content first increased and then decreased;after one year of decomposition,the TC residual rate of the 5 decomposition classes of CWD was all around 50%,and the Mg residual rate of classes I,II,and III was 30%.TC and Mg were all net released.TP of classes I and III are shown as net release,and TN,TP,TK and Ca of class V are all shown as net accumulation.【Conclusion】Although there is a net release of elements,the release rate of TC and other key elements is slow,so coarse woody debris in secondary broad-leaved forest is an important C pool and a long-term source of elements in the forest.