Staff Scientist Oak Ridge National Laboratory Knoxville, Tennessee
Plant roots are colonized by microorganisms that influence plant growth and health. Variation in host phenotype and abiotic factors alter plant-microbe interactions and may scale to affect key ecosystem processes like soil organic matter (SOM) partitioning between mineral-associated and particulate pools, consequently influencing the retention time of SOM. A greater understanding of the factors involved in SOM partitioning is needed to leverage plant-microbe interactions to increase sustainability in managed ecosystems and to accurately model how future climate scenarios will impact SOM cycling. Therefore, we utilized Populus trichocarpa, a foundational tree species in forested ecosystems and a potential bioenergy tree, to investigate how differences in plant metabolites influence belowground microbial communities and SOM partitioning. We hypothesized that variation in plant metabolites would alter plant associated microbial communities, and that collectively these host-microbe interactions would impact SOM partitioning.
To investigate this hypothesis, we collected roots, rhizosphere, and bulk soil from select plant genotypes in a common garden in Davis, CA where Populus trees have been grown under full and reduced irrigation. We characterized archaeal/bacterial and fungal community composition using targeted amplicon sequencing. We quantified soil organic carbon and nitrogen following size-based fractionation of mineral-associated and particulate SOM. We found that SOM is higher under drought conditions when compared to control. We observed a significant positive correlation between concentrations of ferulic acid in P. trichocarpa and mineral-associated organic carbon. Bacterial/archaeal and fungal community composition in the bulk soil and rhizosphere were significantly impacted by drought, and microbial community composition was correlated with soil OM composition. These results indicate that variation in host chemistry influences SOM partitioning, and that differences in SOM partitioning may be driven by plant-associated microbial communities. Collectively, our results suggest that plant genotype selection in managed ecosystems may be leveraged to drive long term retention of soil organic carbon.