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

Abstract To explain the relationship between rhizosphere fungal 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, we found Ascomycota and Basidiomycota were the dominant fungal groups in all treatments. Drought affected the alpha diversity, Chao1, Pielou-e, Shannon, and Simpson indices in LD were the highest under severe stress, Chao1 index in QS and in GN was highest under moderate stress, whereas Pielou-e, Shannon, and Simpson indices were the highest under their respective controls. With increasing drought stress, gibberellin (GA 3 ) and zeatin (ZA) contents and GA 3 /abscisic acid (ABA) increased first and then decreased in the roots and were the highest 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 results suggested that GA 3 (12.8%) and GA 3 /ABA (12.7%) were important driving factors for fungal composition.