干出和沉水不同条件下羊栖菜光合作用碳源获得机制比较(英文)

经济海洋褐藻羊栖菜(Hizikia fusiforme(Harv.)Okamura)低潮时常常周期性地暴露于空气中。为了认识这种海藻在潮汐循环背景下的光合特征,对其在高潮沉水和低潮干出不同条件下的光合作用碳素获得机制进行了比较。沉水时,羊栖菜主要利用海水中HCO_3~-作为外源无机碳源驱动光合作用;而在干出条件下,其光合作用的主要碳源为空气中的CO_2。在这两种不同环境条件下,光合作用与pH值的关系不同:沉水状态时,羊栖菜在高pH值(10.0)下光合活性很弱;而在干出条件下,羊栖菜在高pH值时仍有较高的光合活性。然而,光合作用无论是在沉水还是在干出条件下,对外源碳源的获得都表现出对胞外碳酸酐酶(CA)强烈的依赖性,并且其光合速率都受周围环境中无机碳源水平的限制。此外,在沉水和干出两种环境条件下,羊栖菜光合作用都表现出对氧气的敏感性。这表明,在羊栖菜中,依赖胞外CA的碳源获得机制不能使细胞内CO_2浓度提高到阻碍其光呼吸的程度。增加空气中或海水中无机碳的浓度,能促进羊栖菜的光合作用,进而增加这种海藻的水产养殖产量。

Comparative Mechanisms of Photosynthetic Carbon Acquisitionin Hizikiafusiforme Under Submersed and Emersed Conditions

The economic seaweed Hizikia fusiforme (Harv.) Okamura (Sargassaceae, Phaeophyta) usually experiences periodical exposures to air at low tide. Photosynthetic carbon acquisition mechanisms were comparatively studied under submersed and emersed conditions in order to establish a general understanding of its photosynthetic characteristics associated with tidal cycles. When submersed in seawater, H.fusiforme was capable of acquiring HCO3^- as a source of inorganic carbon (Ci) to drive photosynthesis, while emersed and exposed to air, it used atmospheric 002 for photosynthesis. The pH changes surroundingthe H.fusiforme fronds had less influence on the photosynthetic rates under emersed condition than under submersed condition. When the pH was as high as 10.0, emersed H.fusiforme could photosynthesize efficiently, but the submersed alga exhibited very poor photosynthesis. Extracellular carbonic anhydrase (CA) played an important role in the photosynthetic acquisitions of exogenous Ci in water as well as in air. Both the concentrations of dissolved inorganic carbon in general seawater and CO2 in air were demonstrated to limit the photosynthesis of H.fusiforme, which was sensitive to O2. It appeared that the exogenous carbon acquisition system, being dependent of external CA activity, operates in a way not enough to raise intracellular CO2 level to prevent photorespiration. The inability of H.fusiforme to achieve its maximum photosynthetic rate at the current ambient Ci levels under both submersed and emersed conditions suggested that the yield of aquaculture for this economic species would respond profitably to future increases in CO2 concentration in the sea and air.