毛竹入侵常绿阔叶林对土壤异养硝化作用的影响及其微生物学机理

Moso bamboo (Phyllostachys edulis) invasion is pervasive in subtropical region and becoming increasingly serious. Heterotrophic nitrification is the predominant NO3− production pathway. However, the effects and microbial mechanism of soil heterotrophic nitrification during the Moso bamboo invasion remains largely uncertain. In this research, we will select evergreen broad-leaved forest, bamboo broad-leaved mixed forest, and pure bamboo stands as the study subject. Based on field monitoring data, 15N isotope tracer technique, acetylene inhibition, applied with 13C isotope tracer technique, antibiotic inhibition, nuclear magnetic resonance and high-throughput sequencing were used to assess the effects of plant invasion on soil nitrogen mineralization and related soil microbial community. This research is divided into these parts: the characteristics of mineral N production, changes of microbial community in forest soil, the coupling relationship between microorganism and nitrogen mineralization and nitrification, and the dynamical features of the fungi and bacteria community succession caused by the change of soil organic carbon and its component. Then the effects of Moso bamboo invasion on the characteristics of soil nitrogen mineralization and heterotrophic nitrification are revealed. And the molecular mechanism of heterotrophic and autotrophic nitrification mediated by fungi and ammonia-oxidation microbial communities in different soil is parsed, respectively. Meanwhile, the driving mechanism of microbial community ecological succession affected by the change of soil organic carbon substrates is verified. Finally, we can systematically clarify the driving factors and the microbial mechanism in the process of soil nitrogen mineralization and nitrification caused by Moso bamboo invasion. This study can provide fundamental basis for verifying the ecological mechanisms of Moso bamboo invasion.

毛竹入侵现象在亚热带地区普遍存在并日益严重，异养硝化作用是亚热带酸性森林土壤中生产硝态氮的主要途径，但毛竹入侵常绿阔叶林对土壤异养硝化作用的影响及其微生学机理尚缺乏系统研究。本研究拟以常绿阔叶林、竹-阔混交林及毛竹纯林等不同入侵阶段的林分为研究对象，应用15N同位素示踪、13C同位素示踪微生物核酸技术、核磁共振以及高通量测序等方法，研究不同入侵阶段林分土壤矿质氮生产与微生物群落的变化特征，土壤氮素矿化、硝化过程与微生物的耦合规律，以及土壤有机碳组分的变化与真菌和细菌群落演替的关系，明确毛竹入侵对土壤氮素矿化特征及异养硝化作用的影响方式，揭示不同林分土壤中真菌和细菌群落与氮素矿化和硝化过程的耦合机制，解析毛竹入侵引起土壤有机碳化学结构变化与微生物生长策略的关联，阐明不同林分土壤中真菌、氨氧化菌主导异养硝化、自养硝化的分子机制，研究结果为探明亚热带地区毛竹入侵常绿阔叶林的生态机制提供理论基础。

毛竹入侵现象在亚热带地区普遍存在并日益严重，但毛竹入侵常绿阔叶林对土壤氮素矿化影响及其微生物学机制尚缺乏系统研究。针对常绿阔叶林、竹阔混交林、毛竹纯林设置样地，综合应用Real-time PCR、高通量测序、T-RFLP（Terminal Restriction Fragment Length Polymorphism）、基因克隆文库、15N稳定同位素标记、固态核磁共振技术，详细分析了不同入侵阶段林分土壤矿质氮生产与微生物群落特征，特别是土壤氨化、硝化过程与功能菌群的耦合规律，以及土壤有机碳组分变化与真菌和细菌类群演替的关系，结果如下：(1)毛竹入侵阔叶林对土壤氮素矿化的影响存在季节性差异，夏季毛竹林土壤净氮矿化速率最高，而春季阔叶林土壤净氮矿化速率最低。毛竹林土壤中真菌lcc基因有助于增加土壤净氨化和硝化作用。(2)土壤净氨化、硝化速率随着毛竹入侵显著增加，且三种林分土壤氨化速率平均是硝化速率的10.8倍高。毛竹林中增加的净氨化速率与真菌物种组分和功能类群正相关。真菌木质素降解酶基因lcc丰度能够解释67%的净氨化速率变异，氨氧化细菌基因AOB能够解释62%的净硝化速率变异。(3)毛竹入侵阔叶林后土壤烷基碳组分含量下降，但烷氧碳组分含量增加。土壤真菌群落组分与烷基碳组分含量显著相关，烷基碳组分含量能解释32%的真菌丰度变异。毛竹入侵后固碳基因丰度和固碳酶活性分别增加89%和110%，固碳基因丰度与RubisCO酶活性之间呈显著正相关。根瘤菌目是固碳细菌群落中的优势种群，土壤易氧化碳含量是决定固碳细菌群落变异的关键因子。(4)水培实验中毛竹实生苗在高铵硝比处理下，其光合和根系生产较其他处理显著提高；青冈实生苗低铵硝比处理下，其根长、根表面积较其他处理显著增加。盆栽实验中铵态氮浓度的上升有利于毛竹地上部和地下部生物量的积累，在硝态氮浓度增加后木荷、香樟和青冈的地上、地下生物量均得到显著增加。综上，由真菌群落主导的氨化和异养硝化增加了无机氮素供给，加之毛竹与阔叶树种对无机氮形态的偏好吸收对入侵形成正向反馈，研究结果为探明毛竹入侵常绿阔叶林的地下生态机制提供理论基础。