Reverse microdialysis of sucrose stimulates soil fungal and bacterial growth at the microscale

The rhizosphere is a critical microenvironment that plays key roles in plant nutrient availability, largely due to root interactions with rhizospheric microbes. However, we lack suitable methods that can elucidate mechanisms determining rhizospheric community structure and function within the context of a dynamic, undisturbed soil. Microdialysis has been used for low intrusive soil nutrient sampling at the scale of a fine root, with small probes that also enable release of defined compounds. We evaluated whether microdialysis could simulate exudation, by the release of sucrose, and stimulate changes in a soil microbial community, allowing us to determine the microbes that responded most to carbon release.

Microdialysis successfully stimulated growth on probe surfaces of fungi and bacteria, which were extracted and sequenced for identification. Microbial growth was also visualized with scanning electron microscopy. The majority of the species stimulated were classified as fast growing or opportunistic, e.g. yeasts, moulds, proteobacteria and actinobacteriota, which are known to respond quickly (within days) to the release of simple sugars as exudates in the rhizosphere.

The study demonstrates the potential of using microdialysis as a tool to investigate interactions between root exudation and soil microbial community composition, initially for individual compounds and in the future for more complex compositions.