# Interspecific Differences in Carbon and Nitrogen Metabolism and Leaf Epiphytic Bacteria among Three Submerged Macrophytes in Response to Elevated Ammonia Nitrogen Concentrations

## TL;DR

This study explores how three types of underwater plants and their leaf bacteria respond to increased ammonia levels in water.

## Contribution

The study reveals interspecific differences in carbon and nitrogen metabolism and epiphytic bacterial communities among submerged macrophytes under ammonia stress.

## Key findings

- Submerged macrophytes consume soluble carbohydrates and produce free amino acids under ammonia stress.
- Epiphytic bacterial communities show host-specific variations in relative abundance and denitrification effects.
- Ammonia stress leads to divergent epiphytic bacterial responses related to ammonia oxidation and denitrification.

## Abstract

Submerged macrophytes in eutrophic aquatic environments adapt to changes in ammonia nitrogen (NH4-N) levels by modifying their levels of free amino acids (FAAs) and soluble carbohydrates (SCs). As symbionts of submerged macrophytes, epiphytic bacteria have obvious host specificity. In the present study, the interspecific differences in the FAA and SC contents of Hydrilla verticillata (Linn. f.) Roylep, Vallisneria natans Hara and Chara braunii Gmelin and their leaf epiphytic bacterial communities were assessed in response to increased NH4-N concentrations. The results revealed that the response of the three submerged macrophytes to NH4-N stress involved the consumption of SCs and the production of FAAs. The NH4-N concentration had a greater impact on the variation in the FAA content, whereas the variation in the SC content was primarily influenced by the species. At the phylum level, the relative abundance of Nitrospirota on the leaves exhibited specific differences, with the order H. verticillata > V. natans > C. braunii. The dominant genera of epiphytic bacteria with denitrification effects on V. natans, H. verticillata and C. braunii leaves were Halomonas, Acinetobacter and Bacillus, respectively. When faced with NH4-N stress, the variation in epiphytic bacterial populations associated with ammonia oxidation and denitrification among submerged macrophytes could contribute to their divergent responses to heightened nitrogen levels.