华北落叶松人工林土壤有机碳对密度调整响应机制研究

Thinning treatment as an important forest management practices has an important effect on soil carbon sequestration capacity of forest plantations. However, there still exist uncertainties in the trend, magnitude and efficiency of carbon sequestration with regard to thinning treatments in soil organic carbon pools following thinning. In order to reveal the soil carbon stability mechanism, an in situ tracking experiment was conducted in the L. principis-rupprechtii plantation with heavy, medium and light intensity thinning and unthinned control plots in Shanxi province in northern China. Based on the wet-sieving method, the effects of four thinning regimes on soil aggregate structure and organic carbon fractions were examined. A laboratory culture experiment was conducted to reveal the mineralization characteristics of soil organic carbon fractions. It will reveal the protective mechanism of aggregate structure on soil organic carbon under different thinning regimes. In addition, based on molecular biology, we systematic researched the effects of four thinning regimes on soil microbial diversity and soil enzyme activity at micro-scale of soil aggregates to reveal soil organic carbon stability mechanism. This study provides a scientific basis for a more accurate assessment and prediction of soil carbon sink plantations. It also has certain contribution and practical application values to the sustainable management and carbon sequestration management of plantations in the Taiyue Mountain area.

林分密度调整作为一种重要的人工林经营活动，对人工林土壤碳固持能力有重要的影响。目前关于密度调整后森林土壤有机碳库变化的趋势、幅度及其碳汇功能仍存在很大的不确定性。因此，为了深入揭示密度调整对土壤有机碳稳定固持的关键机制，以四种密度调整水平的华北落叶松人工林为研究对象，采用团聚体分级方法，研究土壤团聚体及其有机碳对密度调整的响应特征和规律；结合室内培养试验，阐明密度调整对团聚体的土壤有机碳矿化动力学特征的影响，揭示团聚体结构对有机碳的保护机制；并借助分子生物学技术，阐明土壤微生物群落结构和功能在团聚体有机碳稳定中的生物调控作用以及对密度调控的响应。研究旨在为更加精确地评估和预测密度调整后人工林土壤碳汇功能提供科学依据，同时为山西太岳山地区人工林可持续经营与碳汇对策研究提供科学依据。

以华北落叶松人工林为对象，着眼于密度调控对土壤有机碳特征的影响，深入研究了探究不同密度调控、不同土层土壤团聚体特征，解释土壤团聚体稳定性和团聚体内有机碳的分异规律，阐述土壤中各级团聚体与团聚体内有机碳含量的相关性，结合不同团聚体水平土壤微生物组成和多样性的差异，揭示不同团聚体水平土壤有机质周转速率差异及其控制因素。结果如下：（1）华北落叶松人工林土壤碳氮磷组分受到了密度调控的显著影响。（2）不同密度林分下华北落叶松人工林土壤团聚体质量分布表现为：＞2mm土壤团聚体含量最大，0.25-1mm粒径土壤团聚体含量与1-2mm粒径土壤团聚体含量次之，＜0.25mm的土壤团聚体含量最小；土壤团聚体稳定性随林分密度的增加而先增加后减小，在密度1415株•hm-2的林分内土壤团聚体稳定性最大，林分密度为2100株•hm-2的林分内土壤团聚体稳定性最小；土壤团聚体总有机碳含量、各组分活性有机碳含量整体上随林分密度的增加而呈现先增加后减小的趋势，密度为1415株•hm-2的林分内土壤养分含量最高；（3）土壤团聚体有机碳累积矿化量随培养时间的推移而逐渐增多，在培养前期（29天前）土壤团聚体的有机碳矿化速率迅速降低，后期（29天后）相对稳定并逐渐趋近于“0”；(4）不同密度林分内土壤团聚体微生物含量存在差异，土壤团聚体微生物总量随林分密度的增大而先增加后减少，1415株•hm-2的林分中微生物总量最高；影响土壤团聚体有机碳累计矿化量和矿化速率的因素主要是土壤有机碳含量，大团聚体中真菌及水溶性有机碳对土壤团聚体累积矿化量影响最大，而小粒径团聚体中对土壤团聚体累积矿化量贡献最大的为细菌。