New research from a subtropical plantation in southern China finds that nitrogen pollution reduces microbial necromass carbon in forest soils, regardless of whether the nitrogen arrives as ammonium, urea, or glycine. The three forms cut fungal necromass carbon by roughly 17 to 21 percent, while total soil organic carbon and CO2 emissions stayed flat. That decoupling matters because microbial residues, especially fungal necromass, are a key stable component of soil carbon. The study points to two linked mechanisms: nitrogen shifts the microbial community toward slower-growing, resource-conservative species, and it intensifies phosphorus limitation. Microbes then work harder to scavenge phosphorus, breaking down the very fungal residues that would otherwise accumulate. For carbon accounting and forest management, the takeaway is that bulk soil carbon measurements can miss a quiet loss in the most persistent carbon pool. Nitrogen deposition loads, not just nitrogen form, deserve closer attention in soil carbon models.
