Investigating grass rhizosphere metabolomics in fabricated ecosystems (EcoFABs)

Abstract:

The rhizosphere is a complex environment that is populated with various organisms including bacteria, fungi, and arthropods. Their interactions strongly rely on the exchange of metabolites secreted by roots (i.e., exudates) and microbes. In addition, the mineralization of these compounds is a central process controlling the soil carbon cycle. However, measuring the stability or turnover of rhizosphere metabolites remains a great challenge due to highly dynamic activities of plants and microbiota.

To address this challenge, we grew the model grass Brachypodium distachyon in fabricated ecosystems (EcoFABs) with controlled and reproducible rhizosphere habitats. The plant root exudate pool was partially labeled via injection of ¹³C-labeled amino acid standards into the rhizosphere. We were then able to quantify the turnover time of certain amino acids by tracing the decline of isotope enrichment in the exudate pool.

Our initial results showed that amino acids have distinct and different turnover times. For example, leucine demonstrated longer turnover time than the other amino acids(?), which may result in its stabilization in the rhizosphere. Building upon these results, we are working to introduce different microorganisms into EcoFABs to further explore how different microbial communities affect the exudate turnover and carbon accumulation in the rhizosphere. Our work demonstrates that the EcoFABs combined with the isotope tracing technique provides an important molecular tool to dissect the rhizosphere metabolomics.