Insights Into The Complex Effects Of The Co-invasion Of Two Exotic Plants On Soil Microbe Community Structure

One of the main factors for successful invasion of some exotic species is that they could build plant-soil feedbacks with soil microbial communities in their rhizosphere to facilitate further invasion. Generally, exotic invasive plants could exit different invasion degrees in the invaded ecosystems because gradual succession occurs after successful colonization in new habitats by those invaders arriving from their original distribution area. More importantly, the successful establishment of one exotic species could create a microenvironment in the invaded ecosystems that could increase the possibility of successful colonization of subsequent invaders. Thus, co-invasion of two or more invasive species is therefore likely in some invaded ecosystems. Hence, the determination of the effects of the co-invasion of different invasive species with different cover classes on the structure and diversity of soil microbial communities may lead to a better understanding of the mechanism underlying their successful invasion.Based on this, the present study was carried out by using the new-generation metagenomics that based on the new-generation high throughput sequencing technology to comprehensively analyze the effects of the co-invasion of two invasive species(Erigeron annuus and Solidago canadensis) with different invasion degrees on soil microbial community structure. This study aimed to address the reconstruction effects of the co-invasion of two invasive species with different invasion degrees on soil microbial community structure(including bacteria and fungi). The results of this study can theoretically provide evidence for the Plant-soil feedbacks hypothesis, and then build a platform to better underlying the soil micro-ecological mechanism of the successful co-invasion of two exotic species.The main results of this study are as follows:(1) To a certain extent, the invasion of E. annuus and/or S. canadensis increased the sum of the number of all plants and the number of all species. Meanwhile, the Shannon-Wiener diversity index and Pielou evenness index of the plant community decreased, but the Simpson dominance index of the plant community increased under the invasion of E. annuus and/or S. canadensis with increasing their invasion degree. While, the invasion of E. annuus and/or S. canadensis did not trigger significant effects on soil p H.(2) Compared with the control, the invasion of E. annuus and/or S. canadensis significantly increased the OUT richness, Shannon index and Chao1 index of the soil bacterial community. Meanwhile, the independent invasion of S. canadensis with low invasion degree and the co-invasion of E. annuus and S. canadensis also significantly increased the ACE index of the soil bacterial communities.Compared with the independent invasion of E. annuus or S. canadensis, the co-invasion of E. annuus and S. canadensis obviously increased the ACE index and Chao1 index of the soil bacterial communities.(3) Compared with the control, the invasion of E. annuus and/or S. canadensis significantly increased the Sequence number, OUT richness, Shannon index, ACE index, and Chao1 index, but obviously decreased the Simpson index of the soil fungi communities. There was no significant difference in the alpha-diversity of the soil fungal communities between the independent invasion of E. annuus or S. canadensis and the co-invasion of E. annuus and S. canadensis.The results indicated that the invasion of E. annuus and/or S. canadensis can affect the plant community structure of the invasive region and the changed plant community structure can pose obvious effects on the soil microbial community structure. To a certain extent, the invasion of E. annuus and/or S. canadensis could increase the diversity and richness of soil microbial communities(including bacteria and fungi). Meanwhile, compared with the independent invasion of E. annuus or S. canadensis, the co-invasion of E. annuus and S. canadensis could pose a synergistic effect on the richness of the soil bacterial communities but posed a neutral effect soil fungi community structure. Thus, the invasion of E. annuus and/or S. canadensis could trigger obvious effects on soil microbial communities(including bacteria and fungi) to build a soil microenvironment which could facilitate their further invasion.