Nitrogen pollution is rising: What a new global map means for forest carbon

On a cool spring morning in a northern forest, the ground feels soft underfoot. Mist hangs between the trunks, and the air smells of wet leaves and old humus; the slow alchemy that keeps a forest alive. Beneath the surface, billions of microbes break down organic matter and hair-thin roots exhale, releasing steady pulses of carbon dioxide. This process, known as soil respiration, is one of the largest carbon fluxes on the planet, usually so...