The researchers investigated how forests in China deal with nitrogen (N) pollution by adding a special form of N to forests with different pollution levels. They found that forests could trap a significant amount of the added N, especially in trees. Even under high N pollution levels, forests in China hold onto N well, although nitrate N can be more easily released compared to ammonium N. Nitrates are mostly stored in plant tissues and could help forests store more carbon. More N was taken up by trees in areas with spring thawing. While forests may not store as much N under heavy pollution, they can still retain significant amounts, showing their ability to manage N pollution effectively.