Impact of Exogenous Indoleacetic Acid on Nitrogen Cycling-Associated Bacteria in the Rhizosphere and Eutrophic Water Surrounding Hydrocotyle vulgaris Lam

Abstract

Phytohormones have the potential to enhance the nutrient removal efficiency of aquatic plants in wastewater treatment. Here, we investigated the impact of indoleacetic acid (IAA) on nitrogen removal by Hydrocotyle vulgaris Lam during the remediation process of eutrophic water. This investigation involved evaluating the biological indicators of H. vulgaris Lam, the nitrogen salt removal efficiency in eutrophic water, as well as analyzing the bacterial structure and function in both the rhizosphere and eutrophic water surrounding H. vulgaris Lam. The results indicated that surface-sprayed 50 mg/L IAA significantly stimulated the growth of H. vulgaris Lam, including parameters such as blade number, leaf area, petiole length, stem thickness, stem length, and root length of H. vulgaris Lam. Furthermore, exogenous application of IAA significantly accelerated the nitrogen removal of NH4+−N, NO3−−N and total nitrogen (TN) in eutrophic water by promoting the NH4−N uptake of H. vulgaris Lam and NO3−−N denitrification. These findings suggest a potential application for exogenous IAA to enhance the nitrogen removal of H. vulgaris Lam in eutrophication control.