a laboratory assessment

The brown algae Fucus serratus is one of the major meadow forming algae of the Western Baltic Sea nearshore ecosystem. At the end of summer, those meadows are exposed to local upwelling suddenly increasing the pCO2 and DIC up to 2500 µatm and 2250 µmol/kg resp., for period of days to weeks. This study investigates the growth response of summer's vegetative Fucus serratus to elevated pCO2 (1350 and 4080 µatm) during a 40 days laboratory incubation. After 10 days, increases of growth rates of 20 % and 47 % of the control were observed in the 1350 and 4080 µatm pCO2 treatments respectively. Beyond 20 days, the growth rates collapsed in all treatments due to nutrients shortage, as demonstrated by high C:N ratios (95:1) and low N tissue content (0.04 % of dry weight). The collapse occurs faster at higher pCO2. On day 30, growth rates were reduced by 40 % and 100 % relative to the control at 1350 and 4080 µatm respectively. These results are consistent with a fertilizing effect of elevated pCO2 on Fucus serratus presumably linked to the transition from active HCO3- to passive CO2(aq) uptake. This positive effect is limited by nutrients resources, low seawater dissolved inorganic N and P and shortage of the nutrients reserves accumulated over the previous autumn and winter.

褐藻锯齿墨角藻（Fucus serratus）是西波罗的海近岸生态系统中主要的造草甸藻类之一。夏末时节，此类藻草甸会遭遇局地上升流，致使水体二氧化碳分压（pCO2）与溶解无机碳（Dissolved Inorganic Carbon，DIC）分别升至2500 µatm与2250 µmol/kg，该高碳环境可持续数日至数周。本研究针对夏季营养生长期的锯齿墨角藻，开展了为期40天的室内培养实验，探究其在升高的pCO2（1350与4080 µatm）条件下的生长响应。培养至第10天时，1350 µatm与4080 µatm pCO2处理组的生长速率较对照组分别提升20%与47%。培养20天后，所有处理组的生长速率均因营养盐匮乏出现骤降，该现象可通过较高的碳氮比（95:1）与较低的组织氮含量（干重的0.04%）得到佐证。且pCO2浓度越高，生长速率骤降的速度越快。至第30天时，1350 µatm与4080 µatm处理组的生长速率较对照组分别降低40%与100%。上述结果与升高的pCO2对锯齿墨角藻的施肥效应相符，该效应推测与藻类从主动摄取碳酸氢根（HCO3⁻）转变为被动摄取溶解态二氧化碳（CO₂(aq)）的生理过程相关。但此类促生效应会受到营养盐资源的限制：海水溶解态无机氮与磷含量偏低，且前秋、冬季积累的营养盐储备已耗尽。