Temporally selective modification of the tomato rhizosphere and root microbiome by volcanic ash fertilizer containing micronutrients

Authors: MEHLFERBER, ELIJAH - University Of California; McCue, Kent; FERREL, JON - Azomite Mineral Products, Inc; KOSKELLA, BRITT - Azomite Mineral Products, Inc; KHANNA, RAJNISH - University Of California

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2022
Publication Date: 3/21/2022
Citation: Mehlferber, E., McCue, K.F., Ferrel, J.E., Koskella, B., Khanna, R. 2022. Temporally selective modification of the tomato rhizosphere and root microbiome by volcanic ash fertilizer containing micronutrients. Applied and Environmental Microbiology. 88(7). Article e00049-22. https://doi.org/10.1128/aem.00049-22.
DOI: https://doi.org/10.1128/aem.00049-22

Interpretive Summary: Tomatoes are the number two most consumed vegetable after the potato. Soil health is critical to provide enough nutrients for the growing plant and maximize productivity. Availability of nutrients from the soil is determined both by abundance of those nutrients and the competition or facilitation by other organisms in the soil. The community of organisms in the soil bacteria and fungi are known as the soil microbiome. This can be further divided into those organisms living in the free soil, closely associated with the roots system or within the roots themselves. Other compartments above ground include microorganisms living on the plant and inside the leaves and stems. The nutrients in the soil impact the microbiome. Similarly, the physical characteristics and chemical composition of the soil can affect the microbiome. In this study we looked at the effect of adding a soil amendment derived from volcanic ash on the composition of the microbiome in the soil and roots and correlated that with crop productivity as measured by the number and weight of the tomatoes produced. The addition of the volcanic amendment had a significant effect on the number and kinds of bacteria present as well as affecting the number and total weight of tomatoes produced.

Technical Abstract: Food crops are grown with fertilizers containing nitrogen, phosphorus, and potassium (macronutrients), along with magnesium, calcium, boron, and zinc (micronutrients) at different ratios during their cultivation. Soil and plant associated microbes have been implicated to promote plant growth, stress tolerance, and productivity. However, the high degree of variability across agricultural environments makes it difficult to assess the possible influences of nutrient fertilizers on these microbial communities. Uncovering the underlying mechanisms could lead us to achieving consistently improved food quality and productivity with minimal environmental impacts. For this purpose, we tested a commercially available fertilizer (surface-mined 38-million-year-old volcanic ash deposit AZOMITE®), applied as a supplement to the normal fertilizer program to tomato plants grown in the greenhouse. We examined its impact on the composition of below-ground microbial communities, focusing on those members we identified as “core taxa” that were enriched in the rhizosphere and root endosphere compared to bulk soil, and appeared above their predicted neutral distribution levels in control and treated samples. This analysis revealed that Azomite had little effect on soil or rhizosphere microbial composition overall, but it had a significant, temporally selective influence on the rhizosphere and root associated core taxa. Changes in the composition of the core taxa were correlated to associated functional pathway enrichment of carbohydrate metabolism over shorter chain carbon metabolism, suggesting a conversion of available microbial nutrient source within the roots. This finding exemplifies how the nutrient environment can specifically alter the functional capacity of root-associated bacterial taxa, with potential to improve crop productivity.