Methane (CH4) flux from ecosystems is driven by C1-cycling microorganisms – the methanogens and the methylotrophs. Little is understood about what regulates these communities, complicating predictions about how global change drivers such as nitrogen enrichment will affect methane cycling. Using a nitrogen addition gradient experiment in three Southern California salt marshes, we show that sediment CH4 flux increased linearly with increasing nitrogen addition (1.23 μg CH4 m−2 day−1 for each g N m−2 year−1 applied) after 7 months of fertilization. To test the reason behind this increased CH4 flux, we conducted a microcosm experiment altering both nitrogen and carbon availability under aerobic and anaerobic conditions. Methanogenesis appeared to be both nitrogen and carbon (acetate) limited. N and C each increased methanogenesis by 18%, and together by 44%. In contrast, methanotrophy was stimulated by carbon (methane) addition (830%), but was unchanged by nitrogen addition. Sequence analysis of the sediment methylotroph community with the methanol dehydrogenase gene (mxaF) revealed three distinct clades that fall outside of known lineages. However, in agreement with the microcosm results, methylotroph abundance (assayed by qPCR) and composition (assayed by terminal restriction fragment length polymorphism analysis) did not vary across the experimental nitrogen gradient in the field. Together, these results suggest that nitrogen enrichment to salt marsh sediments increases methane flux by stimulating the methanogen community.
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机译：来自生态系统的甲烷（CH4）流量是由C1循环微生物（产甲烷菌和甲基营养菌）驱动的。人们对如何规范这些社区知之甚少，有关全球变化驱动因素（如氮富集）将如何影响甲烷循环的预测变得复杂。使用南加州三个盐沼的氮添加梯度实验，我们发现沉积物CH4通量随氮添加量的增加而线性增加（1.23μgg CH4 m −2 day −1 受精7个月后，每g N m −2 year -1 。为了测试CH4通量增加的原因，我们进行了一个微观实验，在有氧和厌氧条件下改变氮和碳的利用率。甲烷生成似乎受到氮和碳（乙酸盐）的限制。 N和C分别使甲烷生成增加18％，合起来增加44％。相比之下，甲烷（甲烷化）受碳（甲烷）的添加（830％）的刺激，而氮的添加却没有改变。用甲醇脱氢酶基因（mxaF）对沉积物甲基营养型群落的序列分析揭示了三个不同的进化枝，它们落在已知谱系之外。但是，与微观结果一致，甲基营养体的丰度（通过qPCR测定）和组成（通过末端限制性片段长度多态性分析测定）在整个实验氮梯度中没有变化。总之，这些结果表明，盐沼沉积物的氮富集通过刺激产甲烷菌群落而增加了甲烷通量。
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