外生菌根真菌对退化马尾松林土壤微生物源有机质的调控机制

Soil microorganisms not only control the decomposition of organic matter, but also are an important source of soil organic matter. Ectomycorrhizal is one of the most common mycorrhizal types which plays an vital role in regulation of soil organic matter cycling, but the understanding of the mechanisms therein is still lacking. Pinus massoniana is the most dominant ectomycorrhizal tree species in red soil region of southern China. However, large areas of degraded P. massoniana forests have low density of soil organic matter. A better understanding of the mechanisms of ectomycorrhizal fungi affecting soil organic matter, which could provide a new perspective for increasing soil organic matter sequestration. In this project, the key determiner of affecting the accumulation of microbial-derived organic matter will be analyzed, based on comparing the contribution of plant and microbial-derived organic matter in the P. massoniana forests at different restoration times. The method of mycorrhizal removal coupled with carbon-nitrogen isotope dual-labelling of litter will be applied, to trace the fate of carbon and nitrogen of different quality litters. We will research the competition for nitrogen between plants associated ectomycorrhizal fungi and saprophytic microorganisms to reveal the net effect of microbial metabolism and anabolism of litter, and also to clarify the mechanisms of litter quality how to affect microbial-derived organic matter, and these researches would to improve the hypothesis of ectomycorrhizal competition. The results will be of great scientific value and practical significance for the exploration of soil microbial managements and promotion of the win-win of soil organic matter and carbon sequestration in the degraded P. massoniana plantation.

土壤微生物不仅控制着有机物质的分解，也是土壤有机质的重要来源。外生菌根是最普遍的菌根类型之一，对土壤有机质循环起着重要调控作用，但我们对其中的机制认识还很有限。马尾松是我国南方红壤区最重要的外生菌根树种，然而大面积的退化马尾松林土壤有机质含量低，深入认识外生菌根真菌对土壤有机质的调控机制将为提升土壤有机质提供新的视角。本项目试图在比较不同恢复时间的马尾松林土壤植物和微生物来源的有机质贡献的基础上，分析影响微生物来源有机质积累的关键影响因素；利用菌根去除结合碳氮同位素双标记凋落物的实验，追踪不同质量凋落物中碳和氮的去向，从植物外生菌根真菌与腐生微生物的氮竞争入手揭示其影响微生物代谢与同化凋落物的净效应，阐明凋落物质量对土壤微生物来源有机质的影响机理，完善外生菌根-竞争假说。研究结果将为探索土壤微生物管理措施、提升退化马尾松林土壤有机质和固碳增汇的双赢具有重要科学价值和实践意义。

根据计划任务书，本项目以亚热带退化森林为主要研究对象，研究了不同恢复年限马尾松林中土壤微生物来源碳的动态，探讨了马尾松到阔叶林过程中微生物源碳的差异，分析了外生菌根对不同质量凋落物分解与转化过程的调控，剖析了不同凋落物质量输入下不同稳定性碳组分中微生物来源碳，主要得出了以下结论:.（1）马尾松林恢复中土壤微生物多样性的增加促进了土壤氨基糖和真菌残体碳含量的积累，但对细菌残体碳无显著影响；林下植被芒萁恢复有利于马尾松林氮库、净氮矿化速率、微生物网络复杂性、土壤微生物间的相互作用、细菌群落碳循环和氮固定功能的提升，从而增加了土壤氨基糖和真菌残体碳含量，其中微生物生物量和年凋落物总量是关键影响因素。.（2）马尾松林到阔叶林恢复过程显著增加了土壤微生物残体碳含量，表层土壤微生物残体碳积累速率显著高于深层，但深层土壤有机碳中微生物残体碳占比显著增加，土壤养分有效性和微生物生物量是关键影响因素。.（3）保留菌根处理的凋落叶分解系数比隔离菌根处理的更高，并对高质量凋落叶分解的影响更大，表明外生菌根真菌促进了凋落叶的分解，尤其是高质量凋落叶分解，主要是因为高质量凋落叶具有更高的氮含量；保留菌根处理的激发效应比隔离菌根处理的更高，因此，外生菌根真菌尽管促进了凋落物分解，但对原有有机碳的固持不利。.（4）多树种混交显著增加表层土壤碳组分中微生物、真菌残体碳及其对土壤有机碳的贡献，并且细菌残体碳主要影响矿物结合态有机碳的变化，而真菌则相反；混交提升了退化马尾松林凋落物质量和土壤氮素有效性、微生物碳利用效率和细菌生物量，高质量和低质量凋落物在形成有机碳时具有补偿效应，从而促进土壤碳的积累。.综上，退化马尾松林恢复过程中微生物来源的有机碳显著增加，外生菌根真菌加快凋落物分解，但又导致更大的激发效应，显著影响退化土壤的碳固存过程，提升凋落物质量有利于土壤有机碳和微生物残体碳的积累，为侵蚀退化土壤碳管理提供了科学依据。