Anthropogenic N deposition, fungal gene expression, and an increasing soil carbon sink in the Northern Hemisphere.

Terrestrial ecosystems in the Northern Hemisphere are a globally important sink for anthropogenic CO₂ in the Earth's atmosphere, slowing its accumulation as well as the pace of climate warming. With the use of a long‐term field experiment (ca. 20 yr), we show that the expression of fungal class II peroxidase genes, which encode enzymes mediating the rate‐limiting step of organic matter decay, are significantly downregulated (−60 to −80%) because of increases in anthropogenic N deposition; this response was consistent with a decline in extracellular peroxidase enzyme activity in soil, the slowing of organic‐matter decay, and greater soil C storage. The reduction in peroxidase expression we document here occurred in the absence of a compositional shift in metabolically active fungi, indicating that an overall reduction in peroxidase expression underlies the slowing of decay and increases in soil C storage. This molecular mechanism has global implications for soil C storage and should be represented in coupled climate–biogeochemical models simulating the influence of enhanced terrestrial C storage on atmospheric CO₂ and the future climate of an N‐enriched Earth.