Effects Of Invasive Plant Flaveria Bidentis On The Diversity Of Major Functional Bacteria In Rhizosphere Soil

Flaveria bidentis (Asteraceae), a global invasive plant species of South American origin, hasinvaded in China since the discovery of its occurrence in Hengshui Lake wetland of Hebei Provinceabout a decade ago. The detrimental consequences of the invasion have been well publicized since then,and a few theories have been proposed from many aspects, aiming to understand the invasionmechanisms, but rarely in the aspect of microbe-plant interaction. In the present research, a newhypothesis is proposed that the introduction of F. bidentis would affect the composition of therhizosphere microbial population, not only in overall quantitative traits, but also in the specificfunctional groups of soil microbial populations involved in plant nutrition, which make indirect effect ofthe native plants growth.To test the hypothesis, rhizosphere soil from F. bidentis and Tagetes erecta, one of the non-invasivespecies closest relative of F. bidentis found in China, were obtained and assayed compared with thecontrol soil that without neither of aforementioned plants growing in. The soil was sampled in differentperiods through the life cycle of the test plants, namely the period of seedling, branching and flowering,respectively. The microbes of different functional groups were isolated using selective mediumaccordingly, and the quantity of respective function groups was estimated. Purifications of each clonewere performed for later extraction of genomic DNA for rep-PCR analysis and16S rDNA sequencing,in order to reconstruct the composition of each functional group for further analysis.The quantity analysis revealed that, at flowering period, the quantities of denitrifying bacteria,nitrogen fixing bacteria, inorganic phosphorus bacteria, organic phosphorus bacteria and potassiumbacteria in F. bidentis rhizosphere increased significantly, compared with that of T. erecta and control.At seedling period, the quantities of sulfur bacteria and anti-sulfur bacteria from F. bidentis rhizospherewere more abundant than that of T. erecta and control. However, the quantities of sulfur bacteria andanti-sulfur bacteria from F. bidentis rhizosphere were decreased with the growth of the plant, andeventually showed no significant difference with the control.Based on the rep-PCR fingerprints cluster analysis, the functional bacteria were divided into245clusters from F. bidentis rhizosphere soil, including69nitrogen fixing bacteria,58inorganic phosphorusbacteria,33organic phosphorus bacteria and85potassium bacteria clusters.237functional bacteriaclusters, including72nitrogen fixing bacteria,61inorganic phosphorus bacteria,21organic phosphorusbacteria and83potassium bacteria clusters, were obtained from T. erecta rhizosphere soil. However,only165clusters, including51nitrogen fixing bacteria,37inorganic phosphorus bacteria,11organicphosphorus bacteria and66potassium bacteria clusters were obtained from control. During the sameperiod, the amount of common cluster from the three treats was few, indicating that F. bidentis greatlychanged the bacterial community composition in the rhizosphere soil.The species richness index and shannon index of the nitrogen fixing bacteria, inorganic phosphorusbacteria, organic phosphorus bacteria and potassium bacteria from the soil of F. bidentis were all higher than that of control, and the species evenness index of the four functional bacteria from control soilwere higher than that of F. bidentis. And the three diversity indices of nitrogen fixing bacteria, inorganicphosphorus bacteria and potassium bacteria from the soil of F. bidentis were all higher than that of T.erecta. It was demonstrated that the nitrogen fixing bacteria, inorganic phosphorus bacteria andpotassium bacteria in the soil of F. bidentis was more abundant and stable than that of T. erecta andcontrol.The identification results of functional bacteria showed that the types of nitrogen fixing bacteria,inorganic phosphorus, organic phosphorus and potassium bacteria from the soil of F. bidentis weresignificantly different from that of T. erecta and control in the process of plant growth. At seedlingperiod, the advantages of the four functional bacteria from the three soils were not identical, but withthe growth of the plant until the flowering period, the advantages of the four functional bacteria fromthe soil of F. bidentis were gradually consistent with that of T. erecta and control.