Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.
Environ Microbiol. 2011 Apr;13(4):854-71. doi: 10.1111/j.1462-2920.2010.02402.x. Epub 2011 Jan 18.
We report N(2) fixation rates measured from two stations monitored monthly off the Mediterranean coast of Israel during 2006 and 2007, and along a transect from Israel to Crete in September 2008. Analyses of time-series data revealed expression of nifH genes from diazotrophs in nifH clusters I and II, including cyanobacterial bloom-formers Trichodesmium and diatom-Richelia intracellularis associations. However, nifH gene abundance and rates of N(2) fixation were very low in all size fractions measured (> 0.7 µm). Volumetric (15) N uptake ranged from below detection (∼ 36% of > 300 samples) to a high of 0.3 nmol N l(-1) d(-1) and did not vary distinctly with depth or season. Areal N(2) fixation averaged ∼ 1 to 4 µmol N m(-2) d(-1) and contributed only ∼ 1% and 2% of new production and ∼ 0.25% and 0.5% of primary production for the mixed (winter) and stratified (spring-fall) periods respectively. N(2) fixation rates along the 2008 east-west transect were also extremely low (0-0.04 nmol N l(-1) d(-1), integrated average 2.6 µmol N m(-2) d(-1) ) with 37% of samples below detection and no discernable difference between stations. We demonstrate that diazotrophy and N(2) fixation contribute only a minor amount of new N to the P impoverished eastern Mediterranean Sea.
我们报告了 2006 年和 2007 年期间每月在以色列地中海沿岸监测到的两个站点的 N2 固定率，以及 2008 年 9 月从以色列到克里特岛的一条横断线上的 N2 固定率。时间序列数据分析揭示了在 nifH 簇 I 和 II 中来自固氮生物的 nifH 基因的表达，包括蓝藻形成的束毛藻和硅藻- Richelia 内共生体。然而，在所测量的所有粒径（> 0.7 µm）中，nifH 基因丰度和 N2 固定率都非常低（> 300 个样本中有 36%低于检测限）。体积（15）N 吸收范围从低于检测限（∼ 36%的> 300 个样本）到高达 0.3 nmol N l(-1) d(-1)，且不随深度或季节而明显变化。区域 N2 固定率平均约为 1 至 4 µmol N m(-2) d(-1)，仅分别占混合（冬季）和分层（春季-秋季）期新生产力的 1%和 2%，以及初级生产力的 0.25%和 0.5%。2008 年东西向横断线上的 N2 固定率也极低（0-0.04 nmol N l(-1) d(-1)，综合平均值为 2.6 µmol N m(-2) d(-1)），有 37%的样本低于检测限，且各站点之间没有明显差异。我们证明，固氮作用和 N2 固定仅为贫瘠的东地中海提供了少量新氮。
