毛竹林生态系统碳-氮耦合循环过程的土壤微生物调控机制

The progresses of fixation and decomposition of forest soil organic carbon are limited by availability and concentration of nitrogen (N), especially by the processes of nitrification and denitrification mediated by soil microorganisms. Forest management changes and human disturbance are the key factors influencing various N cycling pathways. There has been few researches focusing on the characteristics and coupling relationships of soil organic carbon and nitrogen in Phyllostachys pubescens ecosystem from the view of soil functional microorganisms. This study aims to investigate soil organic carbon fractions characteristics, availability of nitrogen species and δ15N abundance of total nitrogen, together with quantitative analyses of ribulose -1,5-bisphosphate carboxylase/ oxygenase (RubisCO) large-subunit genes (cbbL) , and ammonia oxidation and denitrification process related to the functional microorganisms, by using next generation sequencing and stable isotope probing of active microorganisms at natural formation, extensive management and inventively management maoso bamboo soil. This proposal focuses on the key processes of carbon-nitrogen coupling cycles and microbial regulation mechanisms in Bamboo soil ecosystems. We anticipate to make a few progresses in mechanistic understanding of functional coupling of carbon cycle and nitrogen cycle and its microbial mechanism in Bamboo ecosystems and to provide the useful guide for enhancement soil carbon sequestration and reduce N losses in the forest.

森林土壤碳的固定和有机碳的分解过程，受氮素养分含量和可利用性等因素制约，尤其是微生物介导的硝化和反硝化过程，而森林利用类型变化以及人为干扰是造成氮素循环不确定性的因素。从土壤微生物角度研究毛竹林土壤碳氮循环过程，阐明毛竹林土壤相关功能微生物类群与土壤碳−氮耦合循环过程的研究，则鲜少涉及。本项目针对自然形成、粗放经营及集约管理的毛竹林土壤，拟开展土壤有机碳组分特征、有效氮的种类和总氮δ15N丰度，以及CO2同化相关的固碳细菌和RubisCO酶，以及硝化和反硝化微生物功能类群结构和丰度研究，并辅以同位素标记（13C）和DNA/RNA-SIP等先进技术，揭示毛竹林生态系统碳氮耦合循环过程及其微生物学调控机制。项目实施和完成，有望阐明阔叶林或杉木林改种毛竹后（森林类型变化）以及集约经营后（管理措施变化）土壤碳−氮耦合循环过程的变化规律，对增强毛竹林生态系统的碳汇功能和减少氮素损失具有实践意义。

毛竹入侵、粗放经营和集约经营过程中，土壤碳氮循环比天然林生态系统活跃，入侵过程中竹林土壤碳氮含量大于天然林，经营过程中则基本呈短期增加、后下降、最后回升的S型规律，土壤碳氮呈同步耦合关系；毛竹林土壤碳氮含量与碳氮固定微生物基因丰度以及土壤δ13C和δ15N变化规律也基本一致。毛竹林土壤C:N小于天然林、随着毛竹经营时间增加土壤C:N 明显下降。毛竹林土壤微生物网络结构复杂度下降，但碳氮循环的功能反而增加，土壤碳含量呈积累趋势。驱动毛竹林土壤碳−氮耦合循环过程变化的主要因子差别较大，没能发现完全一致的因子；毛竹生态系统中植物和微生物均参与土壤碳氮循环，低纬度或者毛竹林集约经营措施生态系统中土壤微生物对碳氮循环作用大于植物，海拔较高则植物的作用占优势。毛竹林生态森林生态主要表现为积极功能，从土壤生态功方面评价不存在其他人工林长期连载的土壤退化现象。