Coupled treatment of wet-dry alternation irrigation and seedling-promoting fertilizer has a beneficial effect on the rhizosphere microbial community profile and regenerating physiology of ratoon rice

Reasonable water and nitrogen management is a key measure to promote root function and improve the axillary bud germination rate and yield of ratoon rice. However, the effects of water and nitrogen management on root physiology and rhizosphere microorganisms in ratoon rice are largely unclear. This study focused on endogenous hormones in the roots and the rhizosphere microbial community structure of ratoon rice under different water and seedling-promoting fertilizer treatments. The endogenous hormones in the root-stem junctions and the rhizosphere bacterial community structure varied significantly between the wet-dry alternation irrigation coupled with the application of seedling-promoting nitrogen fertilizer (WDN), wet-dry alternation irrigation without nitrogen application (WD), and flood irrigation without nitrogen application (FI). Compared with WD and FI, WDN significantly increased auxin content by 8.13 and 4.83 times and by 14.52 and 14.50 times in the root-stem junctions at the 5th and 10th days after treatment, respectively, and gibberellin A(3) content by 16.70% and 29.74% at the 10th day, respectively. The WDN treatment also significantly increased the diversity and evenness indices of rhizosphere bacterial communities, as well as the relative abundances of plant growth-promoting rhizobacteria, including Brevibacillus, Paenibacillus, Rhizobium, and Clostridium. The white root number and the contribution of the white root weight to the total root weights of ratoon rice in the WDN treatment were significantly higher than those in the WD and FI treatments by 34.41% and 25.98% and by 220.51% and 190.16%, respectively. The results showed that the WDN could significantly increase the levels of endogenous hormones related to root primordium formation and root elongation and improve the population of bacteria related to nutrient cycling and growth promotion in the rhizosphere soil. These improvements significantly promoted the new roots and the growth of low nodal axillary buds, and increased the yield of ratooning rice. The results provide guidance for improving the rhizosphere cultivation of ratooning rice.