Global change drivers that modify the quality and quantity of litter inputs to soil affect greenhouse gas fluxes, and thereby constitute a feedback to climate change. Carbon cycling in the Yukon–Kuskokwim (Y–K) River Delta, a subarctic wetland system, is influenced by landscape variations in litter quality and quantity generated by herbivores (migratory birds) that create ‘grazing lawns’ of short stature, nitrogen-rich vegetation. To identify the mechanisms by which these changes in litter inputs affect soil carbon balance, we independently manipulated qualities and quantities of litter representative of levels found in the Y–K Delta in a fully factorial microcosm experiment. We measured CO₂ fluxes from these microcosms weekly. To help us identify how litter inputs influenced greenhouse gas fluxes, we sequenced soil fungal and bacterial communities, and measured soil microbial biomass carbon, dissolved carbon, inorganic nitrogen, and enzyme activity. We found that positive correlations between litter input quantity and CO₂ flux were dependent upon litter type, due to differences in litter stoichiometry and changes to the structure of decomposer communities, especially the soil fungi. These community shifts were particularly pronounced when litter was added in the form of herbivore feces, and in litter input treatments that induced nitrogen limitation (i.e., senesced litter). The sensitivity of carbon cycling to litter quality and quantity in this system demonstrates that herbivores can strongly impact greenhouse gas fluxes through their influence on plant growth and tissue chemistry.

Graphical abstract

中文翻译：

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食草动物通过改变亚北极湿地的凋落物质量和数量来影响生物地球化学过程

全球变化驱动因素改变了土壤垃圾输入的质量和数量，影响温室气体通量，从而构成对气候变化的反馈。育空-库斯科奎姆 (Y-K) 河三角洲是一个亚北极湿地系统，其碳循环受到草食动物（候鸟）产生的凋落物质量和数量的景观变化的影响，这些草食动物（候鸟）创造了身材矮小、富含氮的“放牧草坪”植被。为了确定凋落物输入的这些变化影响土壤碳平衡的机制，我们在全因子微观世界实验中独立操纵了代表 Y-K 三角洲水平的凋落物的质量和数量。我们每周测量这些微观世界的 CO ₂通量。为了帮助我们确定凋落物输入如何影响温室气体通量，我们对土壤真菌和细菌群落进行了测序，并测量了土壤微生物生物量碳、溶解碳、无机氮和酶活性。我们发现，由于凋落物化学计量的差异以及分解者群落（尤其是土壤真菌）结构的变化，凋落物输入量和CO _{2通量之间的正相关性取决于凋落物类型。}当以草食动物粪便的形式添加垫料时，以及在诱导氮限制（即衰老垫料）的垫料输入处理中，这些群落变化尤其明显。该系统中碳循环对凋落物质量和数量的敏感性表明，食草动物可以通过影响植物生长和组织化学来强烈影响温室气体通量。

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