丛枝菌根真菌对亚热带次级森林演替过程中氮磷添加的响应机制研究

Subtropical forests as one of the most typical forest ecosystems in China have rich species diversity of plants, animals and microorganisms. However, anthropogenic activities and natural disasters influence biodiversity and ecological function in this region. Arbuscular mycorrhizal (AM) fungi, form mutualistic symbiosis with most land plant species and have an important function in biogeochemical cycling, biodiversity maintenance, and community succession in ecosystems. However, we know little about the response mechanism of AM fungi to simulated nitrogen (N) deposition and phosphorus (P) fertilization during the subtropical forest succession. Therefore, this study will be conducted in the permanent plots of different secondary forest successional stages with N and/or P addition in the Gutianshan National Nature Reserve of Zhejiang Province in southeast China. We will use morphological methods to detect the AM fungal root colonization structures and rates, and soil AM fungal extraradical hyphal and spore densities. We also utilize Illumina MiSeq pyrosequencing technique to detect AM fungal community composition both in root and soil samples. On the basis of the analyses of AM fungal colonization structure, biomass, and community structure, the study here will elucidate the response mechanism of AM fungi to N and/or P fertilization along a subtropical secondary forest succession. These findings will offer us new insights into the function of AM in restoration and reconstruction of disturbed subtropical forest ecosystems under global environmental changes.

亚热带森林作为我国典型的生态系统具有丰富的动植物和微生物多样性；但是人类活动和自然灾害的频发严重干扰生态系统的生物多样性和功能。丛枝菌根(AM)真菌与绝大多数陆地植物形成共生关系，在生态系统的物质循环、多样性维持、以及群落演替过程中具有重要功能。然而，在亚热带破坏生态系统的植被恢复过程中，AM真菌对模拟大气氮沉降和施磷肥的响应机制知之甚少。因此，本项目拟依托建立于浙江古田山亚热带不同次级森林演替阶段的氮磷添加实验固定样地，以AM真菌为研究对象，利用形态学方法分析植物根系内AM真菌侵染结构和土壤中AM真菌的菌丝密度和孢子密度，结合高通量测序技术检测根系和土壤中AM真菌的种类组成。通过对不同处理间AM真菌的侵染结构、生物量、群落组成和多样性分析，阐明AM真菌在亚热带次级森林演替过程中对氮磷添加的响应机制。项目为全面揭示全球环境变化下的亚热带干扰生态系统的植被恢复与重建提供重要的科学依据。

通过本项目的实施，在浙江古田山建立了亚热带森林氮磷添加试验长期固定样地。利用形态学结合高通量DNA测序技术比较研究了两种森林演替阶段丛枝菌根(AM)真菌的生物量、多样性与群落组成对氮磷添加的响应，及其季节动态变化。完成了项目计划书的研究内容和预期目标。主要取得如下成果：氮磷添加处理和季节因素均显著影响AM真菌根外菌丝密度，且存在交互作用。磷添加显著地降低了AM真菌的根外菌丝密度。森林演替阶段显著影响AM真菌的孢子密度，老年林土壤AM真菌孢子密度显著高于年轻林。发现亚热带森林土壤AM真菌的多样性较高，总计获得162个AM真菌分类单元(OTUs)，其中108个为球囊霉目，27个为多样孢囊霉目，24个为原囊霉目，3个为类球囊霉目。尽管季节和演替阶段对于AM真菌群落结构的影响不显著，施肥对AM真菌物种多样性具有一定的影响(P = 0.075)，并显著地影响AM真菌的群落组成(P = 0.001)。研究还发现土壤总磷和pH值是影响AM真菌群落组成的两个重要的环境因子。结构方程模型分析表明，磷添加(输入)显著性直接地、且同时可以通过改变土壤总磷含量进而显著性间接地影响AM真菌的群落组成。