Search

Invasive species can shift the composition of key soil microbial groups, thus creating novel soil microbial communities. To better understand the biological drivers of invasion, we studied plant-microbial interactions in species of the Brachypodium distachyon complex, a model system for functional genomic studies of temperate grasses and bioenergy crops. While Brachypodium hybridum invasion in California is in an incipient stage, threatening natural and agricultural systems, its diploid progenitor species B. distachyon is not invasive in California. We investigated the root, soil, and rhizosphere bacterial composition of Brachypodium hybridum in both its native and invaded range, and of B. distachyon in the native range. We used high-throughput, amplicon sequencing to evaluate if the bacteria associated with these plants differ, and whether biotic controls may be driving B. hybridum invasion. Bacterial community composition of B. hybridum differed based on provenance (native or invaded range) for root, rhizosphere, and bulk soils, as did the abundance of dominant bacterial taxa. Bacteroidetes, Cyanobacteria and Bacillus spp. (species) were significantly more abundant in B. hybridum roots from the invaded range, whereas Proteobacteria, Firmicutes, Erwinia and Pseudomonas were more abundant in the native range roots. Brachypodium hybridum forms novel biotic interactions with a diverse suite of rhizosphere microbes from the invaded range, which may not exert a similar influence within its native range, ostensibly contributing to B. hybridum’s invasiveness. These associated plant microbiomes could inform future management approaches for B. hybridum in its invaded range and could be key to understanding, predicting, and preventing future plant invasions., Funding was provided from USDA NIFA in Seed Grant CA-R-PPA-5101-CG and Hatch Grant CA-R-PPA-5093-H to EA, and Spanish Ministry of Science Grants CGL2016-79790-P and PID2019-108195GB-I00 and Spanish Aragon Government and European Social Found Bioflora A01-20R Grant to PC.

In California, invasive grasses have displaced native plants, transforming much of the endemic coastal sage scrub (CSS) to nonnative grasslands. This has occurred for several reasons, including increased competitive ability of invasive grasses and long-term alterations to the soil environment, called legacy effects. Despite the magnitude of this problem, however, it is not well understood how these legacy effects have altered the soil microbial community and, indirectly, native plant restoration. We assessed the microbial composition of soils collected from an uninvaded CSS community (uninvaded soil) and a nearby 10-ha site from which the invasive grass Harding grass (Phalaris aquaticaL.) was removed after 11 yr of growth (postinvasive soil). We also measured the survival rate, biomass, and length of three CSS species andP. aquaticagrown in both soil types (uninvaded and postinvasive). Our findings indicate thatP. aquaticamay create microbial legacy effects in the soil that likely cause soil conditions inhibitory to the survival rate, biomass, and length of coastal sagebrush, but not the other two native plant species. Specifically, coastal sagebrush growth was lower in the postinvasive soil, which had more Bacteroidetes, Proteobacteria,Agrobacterium,Bradyrhizobium,Rhizobium(R. leguminosarum),Candidatus koribacter,Candidatus solibacter, and rhizophilic arbuscular mycorrhizal fungi, and fewer Planctomycetes, Acidobacteria,Nitrospira, andRubrobactercompared with the uninvaded soil. Shifts in soil microbial community composition such as these can have important implications for restoration strategies in postinvasive sites.