From Leaves to Roots: How Foliar IAA Application Alters Fungal Network in the Rhizosphere and Endosphere of Eucommia ulmoides.

Eucommia ulmoides, a valuable tree species endemic to China, faces challenges such as the limited scale and low prevalence of quality seed resources, slow growth and low utilization rates, leading to a persistent supply-demand gap. Growth hormones play an important role in the plant growth and development, and have been shown to significantly enhance the rooting rate of E. ulmoides. In this study, we employed high-throughput sequencing technology and controlled pot experiments to explore the effects of different concentrations of indole-3-acetic acid (IAA) on the endospheric and rhizospheric fungal communities of E. ulmoides. The results revealed that the application of IAA significantly altered the composition, diversity and function of the fungal communities. The most pronounced changes occurred at an IAA concentration of 1000 µM, with a stronger influence on the rhizospheric fungi than on the endospheric fungi. Futhermore, the application of IAA significantly increased the abundance of beneficial fungi in the endosphere, which are crucial for the growth and health of E. ulmoides. These findings indicate that foliar spraying of IAA could effectively reshape the fungal community structure in both the rhizosphere and endosphere of E. ulmoides, and enrich the beneficial functional microbiota. This study provides novel insights into efficient and sustainable agricultural practices from a microbiological perspective.