Maize roots modulate microbial functional traits in the rhizosphere to mitigate drought stress

Abstract

Drought affects soil C sequestration by altering the availability of nutrients to plants and microorganisms. However, the mechanisms of plant-microbe interactions and the potential role of root hairs, which enlarge the root-soil interface, in maintaining rhizosphere processes under drought remain uncertain. We investigated the effect of a 7-day drought on root gene expression in two maize plants, a root hair-deficient mutant and its corresponding wild-type, and its correlation with rhizosphere functions: microbial growth and enzyme kinetics related to organic matter decomposition. Under drought, roots reduced the expression of several chitinase, acid phosphatase and pathogenesis-related genes. In parallel, drought reduced the maximum enzymatic rate of β-glucosidase and acid phosphatase by 3.5- and 1.9-fold, respectively, while the affinity of these enzymes in the rhizosphere increased by 35 and 71 %, respectively, compared to the well-watered treatment. The effect of drought was more pronounced in the rhizosphere of wild-type maize than in that of the mutant. Notably, leucine aminopeptidase and N-acetylglucosaminidase did not respond to drought. Inhibition by high substrate concentrations was observed for β-glucosidase and acid phosphatase only under drought, highlighting the potential use of the substrate inhibition model as a complementary indicator of altered enzyme systems in response to environmental regulators. Finally, drought prolonged the microbial lag phase by up to 24 hours and reduced the microbial specific growth rate by up to 36 % compared to the well-watered treatment. The maximum specific growth rate recovered after rewetting of the soil, demonstrating the sustainability of microbial function after a short-term drought.