By Abbas Nazil
A study from the University of California, Riverside, challenges long-standing assumptions about how forest soils respond to rising global temperatures and their role in the nitrogen cycle.
For decades, scientists have warned that climate warming would cause forest soils to release more nitrogen gases into the atmosphere, increasing pollution, accelerating global warming, and depriving trees of a critical nutrient for growth.
However, after six years of extensive field research in a temperate forest near Shenyang City, China, the research team found that warming may actually reduce nitrogen emissions in regions where rainfall is limited.
The study, published in the *Proceedings of the National Academy of Sciences*, involved more than 200,000 measurements of soil gases, collected through automated chambers installed across six 108-square-meter forest plots.
The researchers simulated a 2°C increase in temperature, roughly the predicted warming by mid-century, using infrared heaters mounted above the soil to mimic atmospheric heat.
Contrary to expectations, nitric oxide emissions dropped by 19 percent, while nitrous oxide, a potent greenhouse gas, decreased by 16 percent under warming conditions.
Associate Professor Pete Homyak, a co-author of the study, explained that while laboratory experiments suggest warming accelerates microbial activity and nitrogen release, field conditions, especially in drier soils, slow microbial processes due to reduced moisture.
The research highlights the importance of soil moisture as a determining factor in nitrogen cycling.
In forests receiving less than 1,000 millimeters of rainfall annually, warming tends to dry soils, suppressing nitrogen emissions, whereas wetter forests still experience increased nitrogen loss, consistent with earlier predictions.
First author Kai Huang, a postdoctoral scholar from the Chinese Academy of Sciences, noted that while nitrogen remains in drier soils, tree growth did not accelerate, potentially due to drought stress, indicating that nutrient retention alone may not offset climate impacts on forest productivity.
The study provides critical insights for climate modeling, emphasizing that accurate predictions must account for both temperature and soil moisture interactions.
By revealing these nuanced dynamics, the research contributes to a better understanding of forest ecosystems as carbon sinks and their ability to continue absorbing atmospheric carbon under a warming climate.
The findings underscore the need for long-term, high-resolution studies to monitor microbial responses, soil chemistry, and tree growth to inform climate adaptation strategies and improve ecological models.
The team continues to track ecological changes in this and other experimental forest plots worldwide to refine predictions of how warming will shape forest health, nutrient cycles, and carbon sequestration in the coming decades.
