Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates
Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates
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DOI：
10.5194/essd-4-47-2012
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发表时间：
2012-01-01
影响因子：
11.4
通讯作者：
Zehr, J. P.
中科院分区：
文献类型：
--
作者：
Luo, Y. -W.;Doney, S. C.;Zehr, J. P.
海洋固氮微生物是海洋浮游生态系统中的一个重要功能类群。生物固氮（N-2）为生物可利用氮提供了一个重要的新的氮源，并影响初级生产力和向深海输出的有机物。作为收集不同浮游植物功能群生物量和速率的一系列努力之一，我们通过汇编约12 000个蓝藻固氮生物丰度（基于显微镜细胞计数或针对nifH基因的qPCR测定）和N-2固定速率的直接实地测量结果，构建了全球中上层海洋固氮生物数据库。生物量转换系数是根据细胞大小估计的，以将丰度数据转换为固氮生物量。该数据库空间有限，缺乏大面积的海洋区域，特别是印度洋。数据近似为对数正态分布，并且大的方差存在于大多数子数据库中，非零值相差5到8个数量级。报告几何平均值和低于和高于几何平均值的一个几何标准误差的范围，全球海洋中浮游生物的N-2固定率估计为62（52-73）Tg Nyr（-1），全球海洋中浮游生物固氮生物量估计为2.1（1.4-3.1）Tg C（细胞计数）和89（43-150）Tg C（基于nifH的丰度）。报告算术平均值和一个标准误差，这三个总体估计值分别为140 +/- 9.2 Tg Nyr（-1）、18 +/- 1.8 Tg C和590 +/- 70 Tg C。与生物量转换因子无关的不确定性可使全球海洋中浮游重氮营养生物量几何平均数的估计值改变约+/-70%。最近发现，最常用的测量N-2固定的方法低估了真实的比率。因此，可以预期未来的速率测量将使平均N-2注视速率向上移动，并且可能导致对全局N-2注视的显著更高的估计。尽管如此，不断发展的数据库可用于研究海洋N-2固定的时空分布和变化，以验证地球化学估计，并参数化和验证海洋地球化学模型，同时铭记未来的速率测量值可能会上升。
Marine N-2 fixing microorganisms, termed di-azotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen ( N-2) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N-2 fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N-2 fixation rate in the global ocean is estimated to be 62 (52-73) Tg Nyr(-1) and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4-3.1) Tg C from cell counts and to 89 (43-150) Tg C from nifH- based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 +/- 9.2 Tg Nyr(-1), 18 +/- 1.8 Tg C and 590 +/- 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about +/- 70 %. It was recently established that the most commonly applied method used to measure N-2 fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N-2 fixation rate upward and may result in significantly higher estimates for the global N-2 fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N-2 fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future.