Changes in root endogenous hormone levels and rhizosphere fungi diversity in alfalfa under drought stress

To explain the relationship between rhizosphere fungi diversity and community composition of alfalfa under drought stress and endogenous hormones in alfalfa, we used sand culture to investigate the performance of Medicago sativa 'Qingshui' (or QS), M. sativa 'Longdong' (or LD), and M. varia 'Gongnong No. 4' (or GN) with contrasting different degrees of drought tolerance. After 7 days of drought stress treatment, the composition of the fungi community in the rhizosphere of alfalfa underwent significant changes, we found Ascomycota and Basidiomycota were the dominant fungi groups in all treatments, indicating that drought-stressed environments play a crucial role in shaping their communities. The results showed significant effects of drought on the & alpha;-diversity, Chao1, Pielou-e, Shannon and Simpson of rhizospheric fungi. The Simpson index was highest for severe stress in LD, while the Chao1 index was highest for moderate stress in QS and GN. The Pielou-e, Shannon and Simpson indices were highest for their respective controls. In addition, the study found that drought stress had a significant impact on endogenous hormone concentrations in alfalfa roots. As drought stress increased, the levels of gibberellin (GA(3)) and zeatin (ZA), as well as the GA(3)/abscisic acid (ABA) ratio, initially increased and then decreased, with the highest levels observed under moderate stress, indole-3-acetic acid (IAA), IAA/ABA, and (IAA + GA(3) + ZA) /ABA were decreased and were the lowest under severe stress, while ABA content was increased in the roots and was the highest under severe stress. The study found a correlation between the endogenous hormone content of roots and rhizosphere fungi. GA(3) (12.8%) and GA(3)/ABA (12.7%) were identified as significant driving factors in the composition of fungi.