# Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levels

## TL;DR

The study shows that the combination of photorespiration and wildfires helps maintain stable atmospheric oxygen levels over millions of years.

## Contribution

The paper reveals a new regulatory mechanism involving photorespiration and fire that tightly controls oxygen levels.

## Key findings

- High moisture in tropical ecosystems weakens the fire feedback on oxygen levels.
- Photorespiration becomes more effective at higher temperatures, reducing global biomass by 86% at 35% oxygen.
- The combined effects of fire and photorespiration provide tighter oxygen regulation than fire alone.

## Abstract

Atmospheric oxygen concentrations have remained remarkably stable over the past ~400 million years (Myr), suggesting the presence of robust regulatory mechanisms. Because of its sensitivity to oxygen, wildfire was traditionally assumed to control oxygen levels by limiting terrestrial vegetation; however, this feedback is nullified by high moisture levels in tropical ecosystems. Using vegetation modeling, we show that where oxygen-fire effects are dampened by high moisture, photorespiration becomes more effective through increased temperatures. Together, these processes interact to drive an 86% reduction in modeled global biomass when oxygen levels reach 35%. This coregulation imposes substantially tighter control of atmospheric oxygen than wildfire alone, providing previously unknown insights into the spatial and interactive feedbacks that may explain the remarkable stability of oxygen levels since the evolution of forests.

Interactions between wildfire and photorespiration under high O2 strongly regulate Earth’s atmospheric oxygen levels.