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Nitrogen (N) deposition can enhance carbon (C) capture and storage in northern coniferous forests but it may also enhance the demand for phosphorus (P). While it is well established that long‐term N enrichment can decrease decomposition and enhance the accumulation of C in soils, it remains uncertain if a higher demand and acquisition of P influence soil C.We studied microbial phosphorus mobilization and growth within a long‐term N enrichment experiment in a Norway spruce forest, where N deposition was simulated by adding 0, 12.5 or 50 kg N ha−1 year−1 for 21 years (n = 12), by incubating microbial ingrowth cores with needles and humus with low and high P content, and with sand with and without mineral apatite P.Long‐term N enrichment had no effect on microbial P mobilization in needles and humus and did not enhance the positive effect that apatite had on fungal growth. However, it consistently strengthened the retention of C in the soil by decreasing decomposition of needle and humus, both with low and high P content, and by increasing fungal growth in sand‐filled ingrowth cores. Furthermore, we did not find any evidence that higher microbial P mobilization in response to N enrichment affected soil C storage.These results show that long‐term N enrichment in relatively young soils dominated by coniferous trees and ectomycorrhizal fungi can have relatively small impact on microbial P mobilization from organic sources and on the potential to mobilize P from minerals, and subsequently that elevated P demand due to N enrichment is unlikely to lead to a reduction in the soil C accumulation rate. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Increased reactive nitrogen (Nr) deposition has raised the amount of N available to organisms and has greatly altered the transfer of energy through food webs, with major consequences for trophic dynamics. The aim of this review was to: (i) clarify the direct and indirect effects of Nr deposition on forest and lake food webs in N-limited biomes, (ii) compare and contrast how aquatic and terrestrial systems respond to increased Nr deposition, and (iii) identify how the nutrient pathways within and between ecosystems change in response to Nr deposition. We present that Nr deposition releases primary producers from N limitation in both forest and lake ecosystems and raises plants' N content which in turn benefits herbivores with high N requirements. Such trophic effects are coupled with a general decrease in biodiversity caused by different N-use efficiencies; slow-growing species with low rates of N turnover are replaced by fast-growing species with high rates of N turnover. In contrast, Nr deposition diminishes below-ground production in forests, due to a range of mechanisms that reduce microbial biomass, and decreases lake benthic productivity by switching herbivore growth from N to phosphorus (P) limitation, and by intensifying P limitation of benthic fish. The flow of nutrients between ecosystems is expected to change with increasing Nr deposition. Due to higher litter production and more intense precipitation, more terrestrial matter will enter lakes. This will benefit bacteria and will in turn boost the microbial food web. Additionally, Nr deposition promotes emergent insects, which subsidize the terrestrial food web as prey for insectivores or by dying and decomposing on land. So far, most studies have examined Nr-deposition effects on the food web base, whereas our review highlights that changes at the base of food webs substantially impact higher trophic levels and therefore food web structure and functioning. [ABSTRACT FROM AUTHOR]