This giant forest experiment offers hope for carbon storage

Key Points:

• Since 2017, a ring of pipes has blown elevated CO2 (573 ppm) over 180-year-old English oaks in Staffordshire, simulating future atmospheric conditions expected by the 2050s, resulting in increased wood growth compared to untreated trees.
• The study found that soil under CO2-enriched trees released about 29% more usable nitrogen, which trees absorbed to support their extra growth, addressing previous concerns that nitrogen availability limits forest growth under higher CO2.
• Trees stimulate soil microbes by releasing carbon-rich root exudates, accelerating nitrogen release from organic matter by about 30%, while also maintaining a "faster but tighter" nitrogen cycle that minimizes nitrogen loss through leaching or gas emissions.
• Despite increased nitrogen cycling, the forest's nitrogen reserves could be depleted over decades, and future nitrogen limitation risks are heightened due to declining atmospheric nitrogen deposition from pollution reductions.
• The study highlights the need for further research to accurately quantify soil carbon balances under elevated CO2 to determine if soils gain or lose carbon, which is crucial for understanding forests' role in climate change mitigation.