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 h 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.