# The Heterogeneous Effects of Epichloë and Rhizophagus irregularis on the Physiological and Rhizosphere Microbial Community of Festuca rubra

## TL;DR

This study explores how two types of fungi affect the growth and microbial environment of a grass species under different nitrogen conditions.

## Contribution

The study reveals novel insights into the combined effects of AMF and endophytic fungi on plant physiology and rhizosphere microbial communities.

## Key findings

- AMF inoculation significantly affected carbon and sulfur content in Festuca rubra under varying nitrogen conditions.
- Dual colonization by AMF and endophytic fungi influenced underground nitrogen content and transpiration rates.
- Soil extracellular enzyme activity and pH were closely linked to rhizosphere microbial community structures.

## Abstract

In nature, a significant number of plant species form symbiotic associations with microorganisms, with arbuscular mycorrhizal fungi (AMF) and endophytic fungi being two prevalent groups of these partners. However, the ability to establish such symbioses with AMF and endophytic fungi is limited to a small fraction of native grass species. Nitrogen is a crucial nutrient for plant growth, yet it is often a limiting factor, underscoring the importance of understanding how plants acquire it. AMF enhance plant growth by improving nitrogen uptake efficiency, but the combined effects of endophytic fungi and AMF on plant physiology and ecology remain underexplored. To address this knowledge gap, in the present study, we conducted an indoor randomized block experiment to investigate the influence of endophytic fungi and AMF infection on the physiological and ecological attributes of Festuca rubra under various nitrogen regimes. The findings indicated that AMF inoculation significantly affected the total carbon content of F. rubra and the total sulfur concentration in its underground tissues across different nitrogen conditions. Additionally, dual colonization by AMF and endophytic fungi had a significant impact on the underground total nitrogen content of the plants. Furthermore, the complex interactions among AMF, endophytic fungi, and nitrogen availability emerged as critical determinants influencing underground total carbon content, transpiration rates, intercellular carbon dioxide concentrations, and the activity of soil extracellular enzymes in F. rubra. The activity of soil extracellular enzymes and pH significantly affected the structure and diversity of rhizosphere bacterial, fungal, and archaeal communities. AMF enhanced the richness of rhizosphere bacterial communities under low-nitrogen conditions, whereas endophytic fungi infection increased bacterial diversity. Soil extracellular enzyme activity and pH were closely related to the community structures and diversities of rhizosphere bacteria, fungi, and archaea. This study clarifies the effects of AMF and endophytic fungi infection on the physiological and ecological characteristics of F. rubra, significantly contributing to our understanding of the synergistic mechanisms governing the interactions among AMF, endophytic fungi, and their host plants.