Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (NO) and methane (CH). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked NO emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first isotope measurements of NO fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted NO from bomas suggests that on average 91 ± 8% NO was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of NO reduction to N across all sample sites (81 ± 9%), indicating high levels of NO consumption. The abundances of denitrification-related genes and ) were significantly higher than those of nitrification-related genes (: AOA and AOB) in the cattle manure samples taken from the bomas, corroborating NO emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene () also corroborated the high potential for microbial NO reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern NO emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions.

中文翻译：

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双同位素和功能基因分析揭示肯尼亚牲畜圈舍高 N2O 排放背后的机制


由于温室气体（GHG）排放，特别是一氧化二氮（NO）和甲烷（CH），牲畜粪便会导致全球变暖。在撒哈拉以南非洲（SSA）的干旱和半干旱地区，广泛的牧区放牧系统很常见，牛白天在稀树草原上吃草，晚上则被关在围栏（在肯尼亚称为）中。粪便通常不会从沼泽中清除，而是堆积起来，导致当地氮负荷过多，使这些沼泽成为 SSA 中被忽视的 NO 排放热点，目前尚未纳入国家和地区温室气体预算。在这里，我们首次对肯尼亚博马废弃后 0 至 5 年的 37 头牛博马的 NO 通量进行了同位素测量，并对土壤和粪便样本进行了功能基因分析。博马排放的一氧化氮的同位素组成表明，平均 91 ± 8% 的一氧化氮是通过细菌反硝化和/或硝化菌反硝化产生的，不同博马年龄段的差异很小。我们还发现所有样本点的 NO 还原成 N 的水平很高 (81 ± 9%)，表明 NO 消耗水平很高。在牛粪样品中，反硝化相关基因（和）的丰度显着高于硝化相关基因（AOA和AOB），证实了NO排放很大程度上归因于反硝化。还原相关基因 () 的大量丰度也证实了博马中微生物 NO 还原的巨大潜力。因此，通过结合双同位素和功能基因分析，我们能够确定控制这些系统 NO 排放的源过程。 更一般地说，通过将粪便撒在沼泽附近或专门的饲料田上来利用粪便，可以提高稀树草原生产力，同时减少温室气体排放，从而实现双赢。