Communities of nematodes, bacteria and fungi differ among soils of different wild cabbage populations

Plants exhibit significant variation in morphological and chemical traits of shoots and roots in response to an array of biotic and abiotic selection pressures, and this variation in turn affects their interactions with the biotic and abiotic environment. Thus far, most studies examining these interactions have focused on the aboveground domain, which is easier to study than the belowground domain. However, soil organisms significantly affect plant fitness directly through mutualisms e.g. growth promotion, or antagonisms e.g. herbivory and disease. Natural populations of wild Brassica oleracea L. growing along the south coastline of Great Britain exhibit sig-nificant differences in growth form and secondary chemistry. Studies in the field have shown that these differ-ences affect aboveground plant-insect interactions, whereas soil communities have not been explored. We sampled belowground communities of nematodes, bacteria and fungi associated with roots, rhizosphere and bulk soil in five coastal wild cabbage populations in Dorset, England, and found significant differences among these communities. Site-related differences in nematode community composition were primarily found for nematodes in bulk soil and were consistent over two years of sampling. Nematode communities in roots of wild cabbage did not significantly differ across the cabbage populations but did differ between the two years. Results for com-munities in rhizosphere soil were spatially and temporally variable. The composition of nematode communities in cabbage roots differed strongly from those in the rhizosphere and bulk soil, showing that plants attract a subset of nematodes from the bulk soil community. For microbes, we analysed only rhizosphere samples, and found that fungal communities differed more strongly among plant populations than bacterial communities. Thus, while there is spatio-temporal variation in belowground communities, soil and/or plant properties differentially affect the assembly of nematodes, fungi and bacteria.

Automated summary

Plants show significant variation in the morphology and chemical traits of shoots and roots in response to biotic and abiotic selection pressures, and these variations affect their interactions with the environment. Most studies have focused on aboveground interactions, neglecting the belowground domain. However, soil organisms can have significant effects on plant fitness through mutualistic or antagonistic interactions. In this study, significant differences in nematode, bacteria, and fungi communities associated with roots, rhizosphere, and bulk soil were found among wild cabbage populations in England, indicating the impact of soil and plant properties on community assembly.