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Nitrogen (N) deposition has a major impact on litter and soil carbon (C) dynamics in forests. Averaged across ecosystems, N deposition has negative impacts on the abundance and diversity of saprotrophic microbes (fungi and bacteria) and changes their species composition toward more opportunistic species. Concomitant with these changes in microbial communities, changes in enzyme activity occur, with hydrolytic-enzyme activity increasing and oxidative-enzyme activity decreasing. A reduction of oxidative-enzyme activity is usually accompanied by a decline in manganese availability. Genomics data confirm that N addition downregulates genes for oxidative enzymes. In the initial stages of litter decomposition an enhancement has repeatedly been observed, but this effect is transient. Soil respiration, the flux of CO₂ from the soil to the atmosphere, is reduced, with a significant reduction of heterotrophic …