EXPLORING DYNAMICS OF RHIZOSPHERE MICROBIOME ASSEMBLY IN ORGANIC CARROTS (DAUCUS CAROTA SUBSP)

Abstract

Soil that surrounds growing roots is referred to as the rhizosphere and represents a hot spot for microbial activity. Roots modulate the rhizosphere through exudation of metabolites; a factor that drives the recruitment of microorganisms to the rhizosphere from the non-plant- associated bulk soil. In modern agriculture, crop roots can be modified through strategic plant breeding efforts, and evidence suggests that this in turn can modify plant-soil-microbe relationships that may be of consequence to plant and soil properties. This prompts the question: how does novel plant trait breeding affect the chemical composition of root exudates and the vital relationships that they support in the rhizosphere across soil types? To address this question, I assessed the root exudate composition of carrot roots from cultivars of the commonly produced Nantes type and the composition of the associated rhizosphere microbial community across three locations in Wisconsin, USA. Root metabolomes were unique across cultivars in two of the three sites. The soil metabolome, which was expected to be consistent between cultivars, was unique to each site and influenced by cultivar. Both fungal and bacterial communities were correlated with the total metabolome across sites, showing this intrinsic connection between the metabolome and microbiome. Though, site differences exerted stronger impacts on fungal and bacterial ⍺ and β diversity as compared to cultivar breeding history. Environmental conditions dictated inter-site differences which ultimately drove microbiome and metabolome differences in these individual carrot cultivars across sites; cultivar breeding history (heirloom or hybrid) only yielded significant effects at the sandiest site. Overall, this research supports the idea that both local site effects and crop breeding consequences together govern rhizosphere microbiome composition. Future research would be well-served to determine whether there are functional consequences, both for soil biogeochemical properties and plant quality and nutrition.