# How river drying influences greenhouse gas emissions: insights from species and gene shifts

## TL;DR

River drying can reduce greenhouse gas emissions by shifting microbial communities and their functions, turning biofilms from carbon sources to sinks.

## Contribution

The study reveals a mitigation effect of river drying on greenhouse gas emissions through changes in functional genes and taxa.

## Key findings

- CO2 and N2O emissions from biofilms did not increase with more drying due to functional community and gene changes.
- Prolonged drying transformed biofilms from carbon sources to sinks, with emission fluxes ranging from 804.78 to −305.55 mg m2 h2.
- Increased abundance of genes in the Calvin–Benson–Bassham cycle and taxa like gemmatimonadota and pseudomonadota drove this shift.

## Abstract

Drying is threatening global river ecosystems due to climate change, altering community composition and function even upon flow resumption. This mesocosm study investigated the greenhouse gas emissions fluxes and underlying mechanisms from benthic habitats prone to 20–100 days of drying. Results show that CO2 and N2O emissions from biofilms did not increase when drying increased, due to the changes in functional communities and genes. Notable is the transformation of biofilm from carbon source to sink following prolonged drying (mean emission fluxes ranged from 804.78 to −305.55 mg m2 h2). This was mainly due to strong increases in the abundance of genes involved in the Calvin–Benson–Bassham cycle (2.82 × 10−5 to 7.12 × 10−5), and functional taxa such as gemmatimonadota and pseudomonadota. These findings reveal a potential mitigation effect of drying on greenhouse gas emissions from rivers and streams, which could be relevant in the face of climate change.