TEMPO.CO, Jakarta - Long-held assumptions about forests and their response to rising temperatures have been challenged by new research findings. Scientists had previously believed that microbes would move faster and release more nitrogen gas into the air as the soil heats up.
Excess nitrogen oxide and nitrous oxide, potent greenhouse gases, contribute to air pollution. An abundance of NO and N2O is also linked to stronger greenhouse gas effects and depletes the remaining nutrients essential for trees.
Researchers from the University of California Riverside conducted a six-year field study to test this idea. Rather surprisingly, their findings contradicted previous assumptions. The team discovered that in dry summer forests, when the researchers heated up the climate-moderate forests in eastern China, nitric oxide emissions decreased by 19% and nitrous oxide by 16%. This was not due to faster movement, but rather because the microbes slowed down.
As the soil dries up due to heat, microbial activity stalls instead of increasing. Pete Homyak, an associate professor of environmental science at UC Riverside, stated, 'This finding overturns our assumptions', as quoted in a report by Earth on Saturday, December 6, 2025.
While laboratory tests showed that heating could increase nitrogen loss, when simulated in real drought conditions, the microbes stopped in dry soil. The experiments were carried out in Qingyuan County near Shenyang, China, chosen for its sensitive soil and climate.
To mimic atmospheric heating, the team installed infrared heaters over six 108-square-meter forest plots (approximately 1,160 square feet), warming the soil surface as expected in future summer seasons. Automated chambers at each plot periodically closed, capturing and analyzing the gases emitted from the soil.
Changes in Dry Soil Conditions
Over the six years, graduate students and postdoctoral researchers based in China kept the system running, generating over 200,000 measurements to monitor the fluctuation of gas emissions following seasons, rain, and heatwaves.
According to the UC Riverside team's research, dry regions with an annual rainfall of less than 1,000 millimeters are hot and can suppress microbial activity, weakening the nitrogen cycle that produces nitric oxide and nitrous oxide.
Researchers are concerned about the impact of hot conditions on the nitrogen cycle. 'Will forests have enough nutrients to continue absorbing carbon as the Earth gets warmer?' stated Kai Huang, an ecologist and the lead author of the study.
The Impact of Nitrogen Constraints on Climate
Forests are one of the Earth's largest carbon sinks, absorbing more carbon dioxide from the air than they release. Trees can only continue to absorb carbon when they grow, and this growth depends on nitrogen.
If consistent heating depletes nitrogen from the soil as gas, the forest's ability to absorb carbon may weaken. According to the latest data, very little nitrogen gas escapes in dry summer regions. However, regardless, the hot conditions still impede tree growth even if nitrogen remains stored in the soil.
One surprising finding was that if less nitrogen gas leaves the soil, trees should grow faster. However, this did not occur at the end of the research. The team's study reaffirms a series of problems triggered by global warming: the reduced loss of nitrogen from the soil, yet plants struggle to access water due to the decreased quantity.
Read: Indonesia Probes 12 Legal Entities Over Forest Destruction Behind Sumatra Floods
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