# Soil water limitation intensity alters nitrogen cycling at the plant-soil interface in Scots pine mesocosms

## TL;DR

This study shows how drought affects nitrogen cycling in soil and plants, with severe drought slowing nitrogen release and altering microbial activity.

## Contribution

The study provides empirical evidence on how progressive water limitation alters nitrogen cycling at the plant-soil interface in Scots pine ecosystems.

## Key findings

- Severe water limitation reduces nitrogen release from decomposing litter and impairs plant nitrogen uptake.
- Moderate drought has minimal impact on microbial nitrogen cycling genes and plant nitrogen uptake.
- Severe drought increases microbial genes linked to water stress tolerance and decreases mineralization and nitrification genes.

## Abstract

More intense episodes of drought are expected to affect terrestrial nitrogen (N) cycling by altering N transformation rates, the functioning of soil microorganisms, and plant N uptake. However, there is limited empirical evidence of how progressive water loss affects N cycling at the plant-soil interface.

We adopted 15N tracing techniques and metagenomic analyzes of microbial genes involved in N cycling to assess how different levels of soil water availability influenced the fate of N derived from decomposing litter in mesocosms with Scots pine saplings.

With increasing water limitation, the release of N from decomposing litter into the soil declined rapidly. However, moderate levels of water limitation barely affected the microbial metagenome associated with N cycling and the uptake of N by the saplings. Comparatively, severe levels of water limitation impaired plant N uptake, and increased the prevalence of microbial N-cycling genes potentially involved in mechanisms that protect against water stress. Genes associated with the uptake and release of N during mineralization and nitrification declined under low soil water contents.

When soil water becomes largely unavailable, the cycling of N at the plant-soil interface is slowed down, and microbial and plant tolerance mechanisms may prevail over N uptake and microbial decomposition.

The online version contains supplementary material available at 10.1007/s11104-025-07758-z.