Low nitrogen (N) availability in the Arctic and Subarctic constrains plant productivity, resulting in low litter inputs to soil. Increased N availability and litter inputs as a result of climate change, therefore, have the potential to impact the functioning of these ecosystems. We examined plant and microbial responses to chronic inorganic N (5 g m⁻² year⁻¹) and/or litter (90 g m⁻² year⁻¹), supplied during three growing seasons. We also compared the response to more extreme additions, where the total cumulative additions of N (that is, 15 g m⁻²) and litter (that is, 270 g m⁻²) were concentrated into a single growth season. Plant productivity was stimulated by N additions and was higher in the extreme addition plots than those with chronic annual additions. Microbial community structure also differed between the chronic and extreme plots, and there was a significant relationship between plant and microbial community structures. Despite differences in microbial structure, the field treatments had no effect on microbial growth or soil C mineralization. However, gross N mineralization was higher in the N addition plots. This led to a lower ratio of soil C mineralization to gross N mineralization, indicating microbial targeting of N-rich organic matter (“microbial N-mining”), likely driven by the increased belowground C-inputs due to stimulated plant productivity. Surprisingly, aboveground litter addition also decreased ratio of soil C mineralization to gross N mineralization. Together, these results suggest that elevated N availability will induce strong responses in tundra ecosystems by promoting plant productivity, driving changes in above- and belowground community structures, and accelerating gross N mineralization. In contrast, increased litter inputs will have subtle effects, primarily altering the ratio between C and N derived from soil organic matter.

北极和亚北极地区的氮（N）利用率低，限制了植物的生产力，导致土壤中的垫料输入量降低。因此，由于气候变化而增加的氮素供应和垃圾输入量有可能影响这些生态系统的功能。我们研究了植物和微生物对三个生长季节提供的慢性无机氮（5 g m - ² 年^-1）和/或凋落物（90 g m - ² 年^-1）的反应。我们还比较了对更极端添加的响应，其中N（即15 g m ^-2）和垫料（即270 g m ^-2）的总累积添加）集中到一个单一的生长季节。氮素的添加促进了植物的生产力，在极端添加地块中，其生产力高于长期每年添加的地块。慢性和极端情节之间的微生物群落结构也不同，并且植物和微生物群落结构之间存在显着的关系。尽管微生物结构不同，但田间处理对微生物生长或土壤碳矿化没有影响。但是，在氮添加区中，总的氮矿化度更高。这导致土壤C矿化与总N矿化的比率降低，表明微生物靶向富含N的有机物（“微生物N采矿”），这可能是由于地下C投入量的增加，这是由于植物生产力的提高所致。出奇，地上凋落物的添加还降低了土壤碳矿化与总氮矿化的比率。总之，这些结果表明，提高氮素利用率将通过提高植物生产力，推动地上和地下社区结构的变化以及加速总氮矿化作用而在苔原生态系统中引起强烈反应。相反，增加的凋落物投入将产生微妙的影响，主要是改变源自土壤有机质的碳氮比。