Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands
Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands
复制标题
DOI：
10.1073/pnas.1515818112
复制
发表时间：
2015-11
期刊：
影响因子：
--
通讯作者：
B. Weber;Dianming Wu;A. Tamm;Nina Ruckteschler;E. Rodríguez‐Caballero;J. Steinkamp;H. Meusel;W. E
中科院分区：
文献类型：
--
作者：
B. Weber;Dianming Wu;A. Tamm;Nina Ruckteschler;E. Rodríguez‐Caballero;J. Steinkamp;H. Meusel;W. E
意义生物土壤结皮(生物结壳)存在于世界各地旱地的地面上，是最古老的生命形式之一，由蓝藻、地衣、苔藓和藻类以及不同比例的异养生物组成。它们通过固定大气中的碳和氮来防止土壤侵蚀和培育生态系统。在这里，我们展示了固定的氮在生物壳内被处理，在这个代谢活动中，氮氧化物和亚硝酸被释放到大气中。这两种气体都是高度相关的，因为它们影响低层大气的自由基形成和氧化能力，也与气候变化相互作用。在旱地，生物结壳似乎在固氮和释放大气活性氮方面发挥着关键作用。活性氮物种对大气化学和气候有很大的影响，将地球的氮循环与生物圈中的微生物活动紧密地联系在一起。然而，它们的来源并没有受到很好的限制，特别是在占全球陆地表面主要部分的干旱地区。在这里，我们展示了生物土壤结皮是一氧化氮(NO)和亚硝酸(HONO)的排放者。最大的通量是由暗蓝藻为主的生物结壳获得的，∼是邻近未生锈土壤的20倍。基于实验室、野外和卫星测量数据，我们得到了全球生物结壳活性氮排放量的最佳估计值∼1.7tg/年(1.1tg a−-1的NO-N和0.6tg a−-1的HONO-N)，相当于天然植被下土壤氮氧化物排放量的∼20%。在大陆范围内，非洲和南美的排放量最高，欧洲最低。我们的结果表明，旱地活性氮的排放在很大程度上是由生物结壳而不是底层土壤驱动的。它们有助于解释全球活性氮排放的测量方法和建模方法之间的神秘差异。由于生物壳的排放强烈依赖于降水事件，影响降水分布和频率的气候变化可能会对陆地活性氮的排放和相关的气候反馈效应产生强烈的影响。由于生物结壳也占全球陆地生物固氮的很大一部分，它们的影响应该进一步量化，并包括在区域和全球大气化学、生物地球化学和气候模式中。
Significance Biological soil crusts (biocrusts), occurring on ground surfaces in drylands throughout the world, are among the oldest life forms consisting of cyanobacteria, lichens, mosses, and algae plus heterotrophic organisms in varying proportions. They prevent soil erosion and nurture ecosystems by fixing carbon and nitrogen from the atmosphere. Here, we show that the fixed nitrogen is processed within the biocrusts, and during this metabolic activity, nitrogen oxide and nitrous acid are released to the atmosphere. Both of these gases are highly relevant, as they influence the radical formation and oxidizing capacity of the lower atmosphere, also interacting with climate change. In drylands, biocrusts appear to play a key role both in nitrogen fixation and the release of atmospheric reactive nitrogen. Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth’s nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a−1 of NO-N and 0.6 Tg a−1 of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.