PS 32-127 - Drought and microbiome effects on maize growth and root metabolomics

Background/Question/Methods

Root exudation is a crucial process that allows plants to interact directly with their rhizosphere environment. Exudates, such as carbohydrates, provide a carbon source for rhizosphere microbes and other exuded compounds, such as organic acids, can directly change rhizosphere soil chemistry. These functions make producing exudates an important plant process when resources, such as water and nutrients, are scarce. To understand the impacts of drought and rhizosphere microbiome on root exudate production and composition, we conducted an experiment to investigate how drought and microbial inoculation affect root and exudate chemical composition (metabolome), using in situ root exudate traps to collect exudate material. We grew Zea mays for six weeks under either full (65% volumetric water content, VWC) or limited (45% VWC) water treatment. Within each watering treatment, half of the plants were inoculated with a microbiome extracted from historically unirrigated agricultural soil and half of the plants were left uninoculated. At the end of the experiment, we analyzed root and exudate metabolite profiles, along with plant gas exchange, growth traits, and soil chemistry to see if plant roots directly exuded compounds in response to their altered environment.

Results/Conclusions

Larger metabolite profile differences were observed in response to the microbiome treatment, even though the watering treatment had a greater impact on plant growth. Uninoculated plants had a higher abundance of many sugars and organic acids as compared to the agricultural microbiome treatment while fully watered plants were more abundant in a handful of organic acids and carbohydrates compared to their half-watered counterparts. The full water treatment tended to produce larger plants with more root biomass than the limited water treatment. Additionally, pore water from the limited water pots was more acidic than the full water treatment. The microbiome treatment had little effect on plant gas exchange, growth, or pore water chemistry. These differences in root tissue profiles were not realized in our root exudate results, likely due to unobserved root damage which caused very high variability in our root exudate samples. These results suggest that, even when plant growth is not noticeably different in response to plant-microbiome status, plant metabolite production is altered to impact how the roots interact with their rhizosphere.