Absolute quantification revealed that glutamate increased the abundance of the rhizosphere bacterial community in Camellia oil tree under drought stress

Kaizheng Lu^1,2Junqin Zhou^1,3,4*Jun Yuan^1,3Jiaqi Qiu⁵Xiaofeng Tan^1,2*

• ¹Key Laboratory of Cultivation and Protection for Non-Wood Forest Trees, Ministry of Education, Central South University Forestry and Technology, Changsha, Hunan Province, China
• ²Academy of Camellia Oil tree, Central South University of Forestry and Technology, Changsha, China
• ³Central South University Forestry and Technology, Changsha, China
• ⁴College of Landscape Architecture, Central South University of Forestry and Technology, Changsha, Hunan Province, China
• ⁵Weichang Manzu Mongol Autonomous County Forestry and Grassland Administration, Chengde, China

Seasonal drought associated with the subtropical monsoon climate significantly impairs the growth and development of Camellia oil tree seedlings. While previous studies have established that drought stress elevates glutamate content in the rhizosphere of Camellia oil tree, the mechanisms through which glutamate modulates rhizosphere microbial community assembly remain unresolved. To investigate the effects of glutamate on the rhizosphere environment under drought stress, we conducted an experiment using three-year-old potted seedlings subjected to moderate drought. These seedlings were irrigated with 50 mL of glutamate solutions at varying concentrations (0, 1, 2, 5, and 10 mmol/L; labeled G0, G1, G2, G5, and G10, respectively). Through analysis of rhizosphere soil nutrients, enzyme activity, and bacterial community abundance (relative and absolute), the study revealed the following: Concentrations of available nitrogen forms (DON, NH₄⁺-N, NO₃⁻-N) increased proportionally with glutamate concentration, whereas soil pH and urease activity exhibited inverse trends. Alpha and beta diversity analyses demonstrated significant divergence in bacterial community composition across treatments. Kruskal-Wallis, ANOVA, and LEfSe analyses identified 24 bacterial phyla significantly associated with treatment differences, with their abundance patterns corresponding to nitrogen cycling gene dynamics-generally peaking at G5 before declining. These findings suggest that 50 mL of 5 mmol/L glutamate represents the optimal concentration for modulating the rhizosphere bacterial community of Camellia oil tree under moderate drought stress.