# Effects of Simulated Precipitation Treatment on Denitrifying Microbial Communities in the Wayan Mountains

## TL;DR

Changing rainfall patterns in the Tibetan Plateau reshape denitrifying microbial communities, affecting nitrogen cycling through soil pH and moisture changes.

## Contribution

The study reveals how precipitation shifts reconfigure denitrifier communities via deterministic processes and environmental filtering.

## Key findings

- Reduced precipitation enriched Ochrobactrum and enhanced nitrogen fixation potential.
- Increased precipitation favored Rhodopseudomonas and strengthened nitrate respiration.
- Soil pH was the dominant environmental driver, with community assembly governed by deterministic processes.

## Abstract

Precipitation regimes on the Qinghai–Tibet Plateau are shifting, yet how these changes affect denitrifying microbes—key regulators of soil nitrogen cycling—remains poorly understood. Through a simulated precipitation experiment in the Wayan Mountain alpine wetland, we show that although short-term precipitation alterations (±25%, ±50%) did not affect the alpha diversity of nirK-type denitrifying communities, they profoundly reshaped community composition and functional potential. Reduced precipitation enriched Ochrobactrum and enhanced nitrogen fixation potential, whereas increased precipitation favored Rhodopseudomonas and strengthened nitrate respiration. Extreme drought suppressed Planctomycetes. Soil pH emerged as the dominant environmental driver, and community assembly was governed entirely by deterministic processes (variable selection). These findings reveal how precipitation modulates denitrifier communities via soil filtering, providing mechanistic insight into nitrogen cycle responses to climate change on the Tibetan Plateau.

The Qinghai–Tibet Plateau is undergoing rapid warming and humidification, with altered precipitation regimes increasingly affecting soil nitrogen cycling and N2O emissions. Denitrification—a key nitrogen transformation pathway—is particularly sensitive to these hydrological changes. Here, we investigated the response of nirK-type denitrifying microbial communities to altered precipitation in an alpine wetland on the northern shore of Qinghai Lake. Using a long-term precipitation manipulation platform with five gradients (ambient, ±25%, and ±50%), we integrated high-throughput sequencing with bioinformatics to systematically assess community shifts. Short-term precipitation treatments did not significantly alter alpha diversity, but markedly restructured community composition. Extreme wetting (+50%) increased within-group heterogeneity. At the phylum level, Proteobacteria remained dominant across all treatments, whereas extreme drought (−50%) suppressed Planctomycetes. At the genus level, Ochrobactrum was enriched under reduced precipitation, while Rhodopseudomonas increased under increased precipitation. Functional predictions indicated that reduced precipitation enhanced nitrogen fixation potential, whereas increased precipitation favored nitrate respiration. Soil pH and carbon fractions were the key environmental filters driving community variation. Ecological process analysis revealed that community assembly was entirely governed by deterministic processes, specifically variable selection. Together, these findings elucidate how precipitation shifts reconfigure the structure and functional potential of denitrifying microbial communities in alpine wetlands, primarily via changes in soil pH and moisture under variable selection. This work provides critical insights into microbial regulation of the nitrogen cycle on the Tibetan Plateau under ongoing climate change.