近岸水域，与外海或大洋相比，生物生产力高，生物同化与异化作用导致明显的pH昼夜变化。这种碳酸盐化学的昼夜变化，与全球海洋酸化相比，可能对生物产生更明显的影响。为此，研究海水碳酸盐系统振荡及其条件下的海洋酸化生理生态效应，是认识近海生物响应酸化机制的重要环节。

高坤山教授课题组以近岸（威氏海链藻，Thalassiosira weissflogii）及大洋硅藻（大洋海链藻，Thalassiosira oceanica）为研究对象，探讨了海水碳酸盐系统昼夜变化条件下CO₂浓度升高（酸化）对其生长及光合生理的影响。结果表明，酸化及海水碳酸盐系统昼夜变化对两种硅藻表现出截然不同的影响。酸化提高威氏海链藻的呼吸作用，促进胞内有机物的生产速率，对其生长没有影响。而大洋海链藻的生长速率明显受到酸化处理的抑制。海水碳酸盐系统昼夜变化对威氏海链藻没有明显影响，却显著降低了大洋海链藻的生长速率及胞内有机物的生产速率。显然，两种不同生态位的硅藻对酸化具有不同的响应，其适应策略也会不同。另外，该结果暗示，浮游植物对碳酸盐系统昼夜变化的适应能力，可能是影响其地理分布的一个重要因素。

该研究成果近日以“Physiological responses of coastal and oceanic diatoms to diurnal fluctuations in seawater carbonate chemistry under two CO₂ concentrations”为题，发表在Biogeosciences期刊上。第一作者为2014级博士生李富田，通讯作者为高坤山教授。 

Figure 1. Measured pH values under different treatments over a diel cycle. LCs (blue closed triangles): steady regime under ambient CO₂ level; LCf (blue open triangles): fluctuating regime under ambient CO₂ level; HCs (red closed circles): steady regime under elevated CO₂ level; HCf (red open circles): fluctuating regime under elevated CO₂ level.

Figure 2 Specific growth rate, respiration rate, POC and PON production rates of the oceanic diatom Thalassiosira oceanica in steady (columns without hatching) and fluctuating  (columns with hatching) regimes under ambient (LC, blue columns) and elevated (HC, red columns) CO₂ levels.

Abstract: Diel and seasonal fluctuations in seawater carbonate chemistry are common in coastal waters, while in the open-ocean carbonate chemistry is much less variable. In both of these environments, ongoing ocean acidification is being superimposed on the natural dynamics of the carbonate buffer system to influence the physiology of phytoplankton. Here, we show that a coastal Thalassiosira weissflogii isolate and an oceanic diatom, Thalassiosira oceanica, respond differentially to diurnal fluctuating carbonate chemistry in current and ocean acidification (OA) scenarios. A fluctuating carbonate chemistry regime showed positive or negligible effects on physiological performance of the coastal species. In contrast, the oceanic species was significantly negatively affected. The fluctuating regime reduced photosynthetic oxygen evolution rates and enhanced dark respiration rates of T. oceanica under ambient CO₂ concentration, while in the OA scenario the fluctuating regime depressed its growth rate, chlorophyll a content, and elemental production rates. These contrasting physiological performances of coastal and oceanic diatoms indicate that they differ in the ability to cope with dynamic pCO₂. We propose that, in addition to the ability to cope with light, nutrient, and predation pressure, the ability to acclimate to dynamic carbonate chemistry may act as one determinant of the spatial distribution of diatom species. Habitat-relevant diurnal changes in seawater carbonate chemistry can interact with OA to differentially affect diatoms in coastal and pelagic waters.

Reference:  Li, F., Wu, Y., Hutchins, D. A., Fu, F., and Gao, K.: Physiological responses of coastal and oceanic diatoms to diurnal fluctuations in seawater carbonate chemistry under two CO₂ concentrations, Biogeosciences, 13, 6247-6259, doi:10.5194/bg-13-6247-2016, 2016.

Link to full text: http://www.biogeosciences.net/13/6247/2016/bg-13-6247-2016.pdf