云冷杉红松林掘根倒木及其微立地对凋落叶分解速率及养分释放的影响

Abstract

采用凋落物分解袋埋藏法，将采集的红松（Pinus koraiensis）、紫椴（Tilia amurensis）和色木槭（Acer mono）凋落叶按自然比例混合装入袋中，于2019年7月将其埋入云冷杉红松林中不同腐烂等级（Ⅱ、Ⅲ、Ⅳ级）的掘根倒木（UT）及其形成的坑底（PB）与丘面（MF）以及对照（包括林隙（FG）和林分（IS））等11种微立地下。8-10月每月从每种微立地取回3袋，处理后测定凋落叶的质量、碳、氮、磷含量。采用相关分析和方差分析的统计分析方法，探究不同微立地下凋落叶的质量、分解速率与养分元素之间的相关性和差异显著性。结果表明：（1）微立地和分解时间对凋落叶质量具有极显著影响（P<0.01）。凋落叶分解90天后，各微立地的凋落叶质量残留率排列为：PB （85.64%） > MF （83.09%） > FG （81.33%） > IS （80.93%） > UT （80.27%）；（2）各微立地的凋落叶分解速率排列为：k_IS=k_UT>k_FG>k_MF>k_PB；Olson指数模型能够较好的模拟各微立地的凋落叶分解动态；年分解速率k为0.61-1.42，分解50%和95%所需时间分别为0.49-1.14 a和2.10-4.92 a。（3）各微立地的凋落叶C残留率总体呈下降趋势，表现为释放模式；UT和MF微立地的N、P残留率持续下降，表现为释放；PB微立地的N、P变化模式分别为释放-富集-释放、富集-释放模式，释放均大于富集，最终表现为释放模式。微立地对凋落叶P释放具有极显著影响（P<0.01），对N释放具有显著影响（P<0.05）；微立地与掘根倒木腐烂等级的交互作用对C、N释放均具有极显著的影响（P<0.01）。（4）凋落叶质量残留率与P的残留率在所有微立地中均存在显著或极显著正相关关系，与N的残留率仅在Ⅱ级UT、PB微立地、Ⅲ级UT微立地、Ⅳ级UT、PB和MF微立地以及FG对照中呈显著或极显著的正相关关系，与C的残留率仅在Ⅱ级UT、PB微立地、Ⅳ级PB、MF微立地中存在极显著或显著正相关关系，与C/N在Ⅱ级UT微立地、Ⅲ级UT、MF微立地和FG对照中呈显著或极显著负相关关系。可见，与不同腐烂等级的掘根倒木相比，掘根倒木形成的微立地环境对凋落叶分解和养分释放的影响较大。;Litter decomposition bag burial method is adopted in this study. The collected litters of Pinus koraiensis, Tilia amurensis, and Acer mono were mixed and packed into bags according to their natural proportion. These bags were buried under eleven different microsites, including uprooted trees (UT) with different decayed levels (Ⅱ, Ⅲ, Ⅳ) and their formed pit bottom (PB), mound face (MF) and the controls (forest gap (FG) and intact stand (IS)) in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest in July 2019. From August to October, three bags of each microsite were collected from each month. After treatment, the mass, C, N and P contents of litters were measured in the labs. Correlation analysis and variance analysis were used to explore their correlations and significance difference between the mass, decomposition rate and nutrient elements of litters at different microsites. The results showed that:(1) microsites and decomposition time had significant effects on the quality of litters(P<0.01). With continuous decomposition, the mass residual rates of litters in each microsite were arranged as follows:PB(85.64%) > MF(83.09%) > FG(81.33%) > IS(80.93%) > UT(80.27%). (2) Their decomposition rates were listed as follows k_IS=k_UT>k_FG>k_MF>k_PB; the Olson index model can simulate the decomposition dynamics of litters in each microsite. The annual decomposition rate k was 0.61-1.42, and the decomposition time required for 50% and 95% was 0.49-1.14 a and 2.10-4.92 a, respectively. (3) The retention rate of C in each microsite showed an overall downward trend, manifested as release mode. The residual rates of N and P in UT and MF microsites continued to decrease, N and P of litters were in the release mode. The change patterns of N and P elements in PB microsites were release-enrichment-release and enrichment-release, respectively. The release was greater than the enrichment, and the final expression was release mode. Microsites had a very significant effect on P release of litters(P<0.01), microsites had a significant effect on N release(P<0.05); the interaction between the microsite and the decay classes of uprooted treefalls had a significant effect on the release of C and N(P<0.01). (4) Retention rate of litter quality and the residual rate of P had a significant or extremely significant positive correlation in all microsites; Retention rate of litter quality and the residual rate of N had a significant or extremely significant positive correlation at level Ⅱ UT, PB microsites, level Ⅲ UT microsites, level Ⅳ UT, PB and MF microsites and FG control; Retention rate of litter quality and the residual rate of C had a significant or extremely significant positive correlation at level Ⅱ UT, PB microsites, Ⅳ PB, MF microsites; retention rate of litter quality and C/N had a significant or extremely significant negative correlation at level Ⅱ UT microsites, Ⅲ UT, MF microsites and FG control. It can be seen that the microsite environment formed by uprooted treefalls has a greater influence on the decomposition and nutrient release of litters than that different decay classes of uprooted treefalls.