Modulation of cadmium uptake in phytoplankton by seawater CO2 concentration
Modulation of cadmium uptake in phytoplankton by seawater CO2 concentration
复制标题
海水 CO2 浓度调节浮游植物对镉的吸收
作者：
J. Cullen;T. Lane;F. Morel;R. Sherrell
镉在海洋中的垂直分布是藻类营养的特征，尽管潜在的生理基础尚未发现。然而，海水中溶解的镉和磷浓度之间的强相关性已被用于重建过去的海洋营养分布。在培养实验中，镉的加入加速了一些海洋浮游植物的生长，并增加了碳酸酐酶的活性，碳酸酐酶通常是一种锌基金属酶，参与无机碳的获取。在这里，我们表明，在海洋硅藻的Cd-碳酸酐酶的浓度，不同的锌-碳酸酐酶的CO2分压（pCO 2），以及锌浓度的调节。在加州中部沿海密集生产性沃茨的实地研究表明，自然浮游植物种群中的镉含量同样会随着地表水pCO 2的降低而增加。培养实验证实，自然浮游植物的镉吸收是负相关的海水pCO 2和锌浓度。因此，我们建议，从海洋表面沃茨中的生物去除镉是其利用碳酸酐酶，并调节溶解的CO2和锌浓度。因此，溶解的海水Cd/P比值将随大气pCO 2而变化，这使得使用镉作为上层海洋过去营养物浓度的示踪剂变得复杂。
The vertical distribution of cadmium in the ocean is characteristic of an algal nutrient, although an underlying physiological basis remains undiscovered. The strong correlation between dissolved cadmium and phosphorus concentrations in sea water has nevertheless been exploited for reconstructing past nutrient distributions in the ocean. In culture experiments, the addition of cadmium accelerates the growth of some marine phytoplankton and increases the activity of carbonic anhydrase, normally a zinc-based metalloenzyme that is involved in inorganic carbon acquisition. Here we show that the concentration of a Cd-carbonic-anhydrase—distinct from Zn-carbonic-anhydrases—in a marine diatom is regulated by the CO2 partial pressure (pCO2) as well as by the zinc concentration. Field studies in intensely productive coastal waters off central California demonstrate that cadmium content in natural phytoplankton populations similarly increases as surface-water pCO2 decreases. Incubation experiments confirm that cadmium uptake by natural phytoplankton is inversely related to seawater pCO2 and zinc concentration. We thus propose that biological removal of cadmium from ocean surface waters is related to its utilization in carbonic anhydrase, and is regulated by dissolved CO2 and zinc concentrations. The dissolved seawater Cd/P ratio would therefore vary with atmospheric pCO2, complicating the use of cadmium as a tracer of past nutrient concentrations in the upper ocean.