Rhizosphere microbial community changes due to weed-weed competition

Many species of weeds are present in agricultural areas, but weeds with greater competitive ability normally become dominant in the field. Rhizosphere soil microbiota can influence weed-weed interactions. However, the role of rhizosphere soil microorganisms in weed-weed interactions remains largely unexplored. In this study, we investigated the ecological relationships and microbial taxa present in the rhizosphere of weeds in monoculture and coexistence systems. The weed species Ageratum conyzoides, Ipomoea ramosissima, and Bidens pilosa were grown in monoculture and coexistence pairs under greenhouse conditions for 80 days. The ecological relationships between weeds were analyzed by calculating the Relative Interaction Index (RII) based on the total dry mass of the plants. The rhizosphere microbiome was analyzed after extracting the metagenomic DNA from rhizosphere microbial populations, followed by PCR amplification and sequencing of the 16S rDNA gene and ITS region, using the Illumina MiSeq platform. Competitive interactions were observed for all combinations of weed species. Ageratum conyzoides showed the greatest decrease in dry matter production due to competition. Weed-weed competition changed rhizosphere microbial community composition and bacterial diversity. The abundance of different bacterial genera in rhizosphere soil varied according to the treatments. When comparing the competition between A. conyzoides and B. pilosa and their respective monocultures, the abundances of Opitutus, Diplorickettisiales uncultured and Bdellovibrio increased in B. pilosa monoculture. When comparing the competition between A. conyzoides and I. ramosissima and their respective monocultures, the abundance of Pseudonocardia increased while the abundance of Fimbriiglobus decreased in A. conyzoides monoculture. Already the abundances of Actinospica, Chitinophaga, Gemmatirosa, 1921-2 and Hymenobacter decreased I. ramosissima monoculture. When comparing the competition between B. pilosa and I. ramosissima, and their respective monocultures, the abundances of Flexibacter and Candidatus Xiphinematobacter decreased I. ramosissima monoculture. The abundances of Clostridium and Rhodobacter increased in competition while the abundance of Pajaroellobacter increased in B. pilosa monoculture. The fungal genera that had their abundances significantly altered were Scytalidium, whose abundance decreased in competition of A. conyzoides and B. pilosa when compared to the respective monocultures, while the abundance of Robillarda increased in B. pilosa monoculture. Already the abundance of Myriodontium increased in B. pilosa monoculture when compared with I. ramosissima monoculture and competition between both plants. Weeds can recruit specific taxa depending on the competition situation in which they are involved. Such changes in the rhizobiome are possibly related to the lower competitive ability and dry matter production of A. conyzoides. B. pilosa have a greater capacity to determine the structure of the rhizobiome when in competition with A. conyzoides. I. ramosissima seem to be less affected by rhizobiome taxon-specific changes.