# Salinity gradients alter root-zone soil microbiome structure and nitrogen-related functional potential in alfalfa (Medicago sativa L.): a pot experiment

## TL;DR

This study shows how different levels of soil salinity affect the soil microbiome and plant growth in alfalfa, highlighting changes in soil chemistry and microbial diversity.

## Contribution

The study integrates soil chemistry, plant growth, and microbiome data to reveal how salinity affects alfalfa root zones.

## Key findings

- Moderate salinity increased soil NO3--N and decreased NH4+-N compared to control conditions.
- Plant height was highest under low salinity, while biomass decreased under salinity treatments.
- Microbial community diversity varied with salinity, though most functional differences were not statistically significant after correction.

## Abstract

Soil salinization constrains agricultural sustainability in arid and semi-arid regions. This study examined integrated soil–plant–microbe responses of alfalfa (Medicago sativa L.) to a salinity gradient.

A pot experiment was conducted with control, low-, and moderate-salinity treatments. Root-zone soil and plants were sampled to measure soil EC, pH, and inorganic nitrogen forms, and to assess plant growth traits. Shotgun metagenomics was used to characterize microbial community composition and metagenome-inferred functional potential.

Salinity increased soil EC and pH and altered inorganic nitrogen forms, with higher NO3--N under moderate salinity and lower NH4+-N under salinity compared with the control. Plant height peaked under low salinity, whereas fresh and dry biomass decreased under both salinity treatments. Microbial β-diversity differed among treatments, while α-diversity showed limited responses. Functional annotations indicated treatment-associated trends in nitrogen- and stress-related categories and KEGG level 3 pathways; however, most differences were not significant after FDR correction.

This integrative root-zone assessment links salinity-driven soil chemistry changes with alfalfa performance and suggests coordinated shifts in soil chemistry, microbiome structure, and plant growth under salinity stress.