Temporally selective modification of the tomato rhizosphere and root microbiome by a dacitic tuff breccia (volcanic ash) containing minerals and trace elements.

Abstract

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.