Seawater carbonate chemistry, primary production, biomass and calcification of plankton and bacteria, 2009

Production (abundance and biomass) and net calcification rates of the coccolithophorid Pleurochrysis carterae under different partial pressures of CO2 (pCO2) were examined using short (15, 24 and 39 h), long (7 d) and dark (7 d) incubation experiments. Short incubations were conducted at ambient, 500 and 820 ppm pCO2 levels in natural seawater that was enriched with nutrients and inoculated with P. carterae. Long incubations were conducted at ambient and 1200 ppm pCO2 levels in natural seawater (0.2 µm filtered as well as unfiltered) that was enriched with nutrients and inoculated with P. carterae. Dark incubations were conducted at ambient and 1200 ppm pCO2 in unfiltered seawater that was inoculated with P. carterae. The abundance and biomass of coccolithophorids increased with pCO2 and time. The abundance and biomass of most noncalcifying phytoplankton also increased, and were hardly affected by CO2 inputs. Net calcification rates were negative in short incubations during the pre-bloom phase regardless of pCO2 levels, indicating dissolution of calcium carbonate. Further, the negative values of net calcification in short incubations became less negative with time. Net calcification rates were positive in long incubations during blooms regardless of pCO2 level, and the rate of calcification increased with pCO2. Our results show that P. carterae may adapt to increased (~1200 ppm) pCO2 level with time, and such increase has little effect on the ecology of noncalcifying groups and hence in ecosystem dynamics. In dark incubations, net calcification rates were negative, with the magnitude being dependent on pCO2 levels.

本研究通过短期（15、24和39 h）、长期（7 d）及黑暗条件（7 d）的培养实验，探究了不同二氧化碳分压（partial pressure of CO2, pCO2）下颗石藻（coccolithophorid）卡特氏扁藻（Pleurochrysis carterae）的生产力（丰度与生物量）及净钙化速率。短期培养实验在添加营养盐并接种卡特氏扁藻的天然海水中开展，设置了环境水平、500 ppm及820 ppm三种pCO2梯度。长期培养实验同样在添加营养盐并接种卡特氏扁藻的天然海水中进行，设置了环境水平与1200 ppm两种pCO2梯度，所用海水分为0.2 μm过滤组与未过滤组。黑暗培养实验则在未过滤且接种卡特氏扁藻的天然海水中开展，设置了环境水平与1200 ppm两种pCO2梯度。研究结果显示，颗石藻的丰度与生物量随pCO2升高及培养时长增加而上升；多数非钙化浮游植物的丰度与生物量亦呈上升趋势，且几乎不受二氧化碳分压变化的影响。在藻华前期的短期培养实验中，无论pCO2水平如何，净钙化速率均为负值，表明碳酸钙发生溶解；且随着培养时长增加，短期培养中的净钙化速率负值逐渐减小。在藻华期的长期培养实验中，无论pCO2水平如何，净钙化速率均为正值，且钙化速率随pCO2升高而提升。本研究表明，卡特氏扁藻可随培养时长逐步适应约1200 ppm的升高pCO2水平；而pCO2升高对非钙化浮游植物类群的生态特征几乎无影响，因此对生态系统动态的作用有限。在黑暗培养实验中，净钙化速率为负值，其绝对值随pCO2水平变化而改变。