植物竞争和昆虫取食调节入侵植物对土壤细菌群落和功能的影响

以入侵植物空心莲子草（Alternanthera philoxeroides （Mart.） Griseb）、本土近缘种莲子草（Alternanthera sessilis（L.） DC）、生防昆虫莲草直胸跳甲（Agasicles hygrophila （Selman&Vogt））和本地昆虫虾钳菜披龟甲（Cassida piperata （Coleoptera：Cassididae））为研究对象，建立3种植物种植方式（空心莲子草单种、莲子草单种、空心莲子草和莲子草混合种植）和4种昆虫取食类型（无昆虫取食、虾钳菜披龟甲取食、莲草直胸跳甲取食、两种昆虫同时取食），通过高通量测序技术探究植物竞争、昆虫取食以及二者交互作用如何调控入侵植物对土壤细菌群落的影响。结果显示，植物竞争、昆虫取食及其交互作用对土壤细菌群落的物种多样性指数（Observed sub-OTUs）、香农指数（Shannon）、系统发育多样性指数（Phylogenetic diversity）和均匀度指数（Evenness）均无显著影响。表明不论是空心莲子草还是莲子草均不影响土壤细菌的alpha多样性，并且植物竞争和昆虫取食对土壤细菌alpha多样性û有调控作用。但植物竞争显著改变了土壤细菌群落结构，降低了绿弯菌和化能异养型细菌的相对丰度，而增加了酸杆菌的相对丰度。同时，植物竞争与昆虫取食的交互作用可以调控空心莲子草对土壤细菌群落结构、优势门类和功能类群的影响，说明生物胁迫对土壤微生物的群落结构和功能具有调控作用。准确评估外来入侵植物的影响时需要考虑其所入侵生境的生物因素。

Plant competition and insect herbivory mediate the impact of invasive plants on soil bacterial community and function

Exotic plant invasion is an important driver of biodiversity loss. However, little is known regarding how exotic species influence biodiversity belowground and whether such impact can be regulated by other biotic stresses, such as plant competition and insect herbivory. In this study, we used the invasive plant Alternanthera philoxeroides (Mart.) Griseb, native congener Alternanthera sessilis (L.) DC, biocontrol agent Agasicles hygrophila (Selman & Vogt), and native insect Cassida piperata (Coleoptera:Cassididae) as a study system. We established three plant combinations (monoculture of Alternanthera philoxeroides, monoculture of Alternanthera sessilis, and mixture of Alternanthera philoxeroides and Alternanthera sessilis) and four insect herbivory treatments (no insect herbivory, Agasicles hygrophila herbivory, C. piperata herbivory, and Agasicles hygrophila + C. piperata herbivory). We examined how plant competition and insect herbivory mediates the impact of invasive plants on soil bacterial community using high throughput sequencing. We found that plant competition, herbivory treatment, and their interaction did not affect the observed sub-operational taxonomic unit (OTU), Shannon, Phylogenetic diversity, and Evenness indices. These results indicated that neither Alternanthera philoxeroides nor Alternanthera sessilis affected alpha diversity of soil bacteria, and plant competition and herbivory did not exert a mediating effect. In contrast, plant competition strongly affected the composition and structure of the soil bacterial community, decreasing the relative abundance of Chlorobacteria and chemoheterotrophic bacteria while increasing the relative abundance of Acidobacteria. Moreover, plant competition and its interaction with herbivory further regulated the impact of Alternanthera philoxeroides on soil bacterial community composition and structure as well as dominant and functional phyla. Our study indicated that such impact was further regulated by other biotic stresses. Therefore, biotic factors should be included when evaluating the impact of invasive species on biodiversity.