Microorganisms at the base of water lilies

Nymphaea candida Presl is a rare and endangered waterlily species, and cultivating robust seedlings suitable for artificial propagation has become a critical issue for the conservation of this species. In this study, Aspergillus fumigatus, an endophytic fungus isolated from the roots of N. candida showed the capability of solubilizing phosphate, potassium and producing siderophores. The application of A. fumigatus significantly increased leaf length, leaf width, leaf number, and root length of N. candida seedlings by 97.83%, 131.37%, 94.12%, and 171.25%, respectively. Meanwhile, A. fumigatus application significantly enhanced soil organic matter content, alkali-hydrolyzable nitrogen content, sucrase activity, and peroxidase activity by 6.57%, 31.62%, 23.26%, and 7.53%, respectively. Moreover, A. fumigatus enriched beneficial microorganisms including Cyanobium, Aquicella, and Cryptomycota to form a more stable rhizosphere soil microenvironment. Additionally, A. fumigatus upregulated genes involved in photosynthesis and photosynthesis-antenna protein pathways in N. candida leaves, with the expression levels of PsbA, PetG, and PsbH significantly increasing by 2.17, 0.28, and 4.48-fold, respectively. Therefore, the isolated endophytic growth-promoting fungus A. fumigatus might be a reliable tool for the propagation of N. candida seedlings, which would be helpful for the conservation of this rare and endangered aquatic plant species.