Dysbiosis of the rhizosphere microbiome caused by γ-irradiation alters the composition of root exudates and reduces phosphorus uptake by rice in flooded soils

Purpose The response of rice (Oryza sativa L.) plants to phosphorus (P) deficiency and to alterations in the rhizosphere microbiome in flooded soils remains unexplored. We aimed to identify the association between alterations in bacterial diversity and underground metabolic and chemical reactions in the rhizosphere in P-deficient and gamma-irradiated conditions. Methods Two rice varieties were grown in a split-root box under flooded conditions and filled with either P-applied or non-P-applied soils with or without gamma-irradiation. At 41-42 days after transplanting, we determined plant biomass, P uptake, exudation rates of total carbon and low-molecular-weight organic acids (LMWOAs) from the roots, and bacterial diversity, P fractions, and phosphatase activity in the rhizosphere. Results gamma-irradiation significantly decreased the P uptake and biomass of both rice varieties and reduced the relative abundance of Alphaproteobacteria and microbiome beta diversity in the rhizosphere. Concurrently, gamma-irradiation reduced the uptake of insoluble P from soils. These microbiological and chemical changes in the gamma-irradiated rhizosphere occurred irrespective of the P treatments of soils. On the contrary, the proportion of LMWOAs and citric acid exudation, which have a high P-solubilization capacity, increased in the gamma-irradiated and P-applied rhizosphere soils at the expense of other carbons. No differences were detected in phosphatase activity in any treatments. Conclusion Dysbiosis of the rhizosphere microbiome negatively affected rice growth and the uptake of insoluble P in flooded soils. With a reduction in microbiome diversity, rice plants may have a complementary strategy to increase the proportion of citric acid exudation toward the P-rich soil area.