Institute of Marine Sciences, University of North Carolina, Morehead City, North Carolina 28557.
Appl Environ Microbiol. 1987 Oct;53(10):2353-62. doi: 10.1128/aem.53.10.2353-2362.1987.
Diel variations in N(2) fixation (acetylene reduction), CO(2) fixation, and oxygen concentrations were measured, on three separate occasions, in a marine microbial mat located on Shackleford Banks, North Carolina. Nitrogenase activity (NA) was found to be inversely correlated with CO(2) fixation and, in two of the three diel periods studied, was higher at night than during the day. Oxygen concentrations within the top 3 mm of the mat ranged from 0 to 400 muM on a diel cycle; anaerobic conditions generally persisted below 4 mm. NA in the mat was profoundly affected by naturally occurring oxygen concentrations. Experimentally elevated oxygen concentrations resulted in a significant depression of NA, whereas the addition of the Photosystem II inhibitor 3(3,4-dichlorophenyl)-1,1-dimethylurea decreased oxygen concentrations within the mat and resulted in a significant short-term enhancement of NA. Mat N(2)-fixing microorganisms include cyanobacteria and heterotrophic, photoautotrophic, and chemolithotrophic eubacteria. Measured (whole-mat) NA is probably due to a combination of the NA of each of these groups of organisms. The relative contributions of each group to whole-mat NA probably varied during diel and seasonal (successional) cycles. Reduced compounds derived from photosynthetic CO(2) fixation appeared to be an important source of energy for NA during the day, whereas heterotrophic or chemolithotrophic utilization of reduced compounds appeared to be an important source of energy for NA at night, under reduced ambient oxygen concentrations. Previous estimates of N(2) fixation calculated on the basis of daytime measurements may have seriously underestimated diel and seasonal nitrogen inputs in mat systems.
我们分别在三次测量了位于北卡罗来纳州 Shackleford Banks 的海洋微生物席中 N2 固定（乙炔还原）、CO2 固定和氧气浓度的日变化。发现固氮酶活性（NA）与 CO2 固定呈负相关，在研究的三个日周期中的两个周期中，夜间的 NA 高于白天。微生物席顶层 3 毫米范围内的氧气浓度在日周期内从 0 到 400 μM 不等；通常在 4 毫米以下保持厌氧条件。席中的 NA 受到自然存在的氧气浓度的强烈影响。实验中升高的氧气浓度会显著抑制 NA，而添加光合作用系统 II 抑制剂 3(3,4-二氯苯基）-1,1-二甲基脲会降低席内的氧气浓度，并导致 NA 短期显著增强。席中固定氮的微生物包括蓝细菌和异养、光自养和化能自养细菌。测量的（整个席）NA 可能是这些生物体组的每个 NA 的组合。每个组对整个席 NA 的相对贡献可能在日周期和季节（演替）周期中发生变化。来自光合作用 CO2 固定的还原化合物似乎是白天 NA 的重要能源来源，而在减少的环境氧气浓度下，异养或化能利用还原化合物似乎是夜间 NA 的重要能源来源。以前基于白天测量值计算的 N2 固定估计可能严重低估了席系统中日周期和季节的氮输入。
