Parasitism changes rhizospheric soil microbial communities of invasive Alternanthera philoxeroides, benefitting the growth of neighboring plants

Parasitic plants represent a peculiar and highly specialized group and are important members of terrestrial ecosystems. Although much is known about how parasitic plants influence growth, reproduction, physiology, and metabolism of host plants, their possible role as modulators of microbial community properties remains largely unexplored. Using next-generation sequencing of the bacterial 16S rRNA gene and fungal rRNA internal transcribed spacer, we analyzed the effects of parasitism on both composition and diversity of soil microbial communities in the rhizosphere of an invasive species Alternanthera philoxeroides parasitized by Cuscuta australis, and feedback effects of parasitism-altered soil microbes on the growth of the host (A. philoxeroides) and on the co-existing native Trifolium repens. Cuscuta australis parasitism increased alpha-diversity and changed the composition of both bacterial and fungal community in the rhizospheric soil of A. philoxeroides. Alternanthera philoxeroides produced significantly less plant biomass when grown in soils inoculated with microbial communities of A. philoxeroides parasitized by C. australis compared to non-parasitized soils and control soils, whereas T. repens produced significantly more biomass grown in soils inoculated with microbial communities of A. philoxeroides parasitized by C. australis. Inoculation with soil microbial communities of A. philoxeroides not parasitized by C. australis increased the competitiveness of A. philoxeroides to neighboring T. repens, whereas, inoculation with soil microbial communities of A. philoxeroides parasitized by C. australis reduced the competitiveness of A. philoxeroides. These results suggest that plant parasitism-induced changes in soil microbiome can negatively affect host plant growth, and positively affect the growth of the native neighbor plants, via shift of the competitive hierarchy between the host and co-existing native plants.