Kinetics of silicic acid uptake by natural diatom assemblages in two Gulf Stream warm-core rings
Kinetics of silicic acid uptake by natural diatom assemblages in two Gulf Stream warm-core rings
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DOI：
10.3354/meps062283
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发表时间：
1990
影响因子：
2.5
通讯作者：
D. Nelson;M. Brzezinski
中科院分区：
文献类型：
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作者：
D. Nelson;M. Brzezinski
我们进行了Si示踪实验，以测量在2个墨西哥湾流暖核环中组装的天然硅藻对硅酸的吸收率作为细胞外硅酸浓度的函数。实验在81-D环和82-B环的中心附近进行，包括5个采样日期，分别是春末、夏季和秋季，在20 - 30 m的上部，常规分析无法检测到硅酸（< 0.2 yM），只有在无法检测到硅酸的站点，才能测量到底物的吸收。在季节性温跃层形成之前，典型的82-B环的Si(OH)4浓度为2.5 ~ 31rm，足以支持最大吸收率。当衬底1i。吸附速率对硅酸浓度的依赖性表现为双曲线饱和动力学，其半饱和常数（K,）在0.53 ~ 0.90 μ m之间。这一范围大大低于以前报道的天然硅藻的范围（1.5至3.7 pM）。数值模拟表明，具有典型环组合K值的硅藻物种在培养过程中，不仅在持续低碳-碳- d浓度的条件下，而且在具有暖核海洋漩涡特征的零星脉冲营养物注入的条件下，都将胜过大多数硅动力学研究过的硅藻物种。以前对天然水体中硅酸吸收动力学的研究都是在相对营养匮乏的系统中进行的，我们在这里报道的2个墨西哥湾流暖核环的低K值表明，生长在营养严重匮乏的地表水中的硅藻比生长在更富营养化栖息地的硅藻对硅酸的依赖性更高。如果在其他营养物枯竭的环境，如热带和洋中环流中也是如此，那么在这些系统中出现显著的海水限制的可能性就降低了。
We performed "Si tracer experiments to measure the uptake rates of silicic acid by natural diatom assemblaged in 2 Gulf Stream warm-core rings as a function of the extracellular silicic acid concentration. The experiments were performed a t and near the centers of rings 81-D and 82-B, and lncluded 5 sampling dates in late spring, summer and autumn, when silicic acid was undetectable to conventional analyses (< 0.2 yM) throughout the upper 20 to 30 m Uptake was measurably substratelimited only at those stations where silicic acid was undetectable. Concentrations of 2.5 to 3 1rM Si(OH)4, which typlfied ring 82-B before the development of the seasonal thermocline, were high enough to support maximum uptake rates. When substrate 1i.mitation was present the dependence of the uptake rate on sllicic acid concentration exhibited hyperbolic saturation kinetics, with half-saturation constants (K,) ranging from 0.53 to 0.90 \&M. This range is considerably lower than that reported previously for natural diatom asselnblages (1.5 to 3.7 pM). A numerical sllnulation indicates that a diatom species with a K, value typical of the ring assemblages would outcompete most diatom species whose silicon kinetics have been examined in culture, not only under conditions of continuously low sll~cic a c ~ d concentration but with the sporadic, pulsed nutrient injections that appear to characterne warm-core ocean eddies. Prevlous studies of silicic acid uptake kinetics in natural waters have all been conducted In relatively nutnent-rlch systems and the lower K, values we report here for 2 Gulf Stream warm-core rings Indicate that diatoms growing in severely nutrient-depleted surface waters have a higher afflnlty for slliclc acid than those growing in more eutrophic habitats. If this is true for other nutrient-depleted environments such as the tropics and mid-ocean gyres, the likelihood of significant slhcon limitation in such systems is diminished.