天津近岸浮游植物群落对海洋酸化和硝酸盐加富的响应

为了评估海洋酸化和富营养化耦合作用对近海浮游生态环境的影响,本研究以天津市近岸海域浮游植物群落的生物地球化学指标为研究对象,分别采用一次性及连续培养的方式模拟自然水华及稳态条件,探究其对二氧化碳(CO₂)和硝酸盐浓度变化及二者耦合作用的响应。实验条件设置如下:1)对照:二氧化碳分压p(CO₂)40.53 Pa、无硝酸盐添加;2)酸化:p(CO₂)101.3 Pa、无硝酸盐添加;3)加N:p(CO₂)40.53 Pa、添加硝酸盐50 μmol·L^–1;4)酸化加N:p(CO₂)101.3 Pa、添加硝酸盐50 μmol·L^–1。实验结果表明,硝酸盐加富比酸化更加显著地促进浮游植物群落总叶绿素(Chl a)生物量及颗粒有机碳(POC)和颗粒有机氮(PON)积累,酸化和加N使浮游植物群落粒径大小升高。连续培养实验表明,酸化和N加富对Chl a、生物硅(BSi)、PON浓度、PON与颗粒有机磷(POP)比值(N/P)、POC与BSi比值(C/BSi)及沉降速率有协同交互作用,对POP和POC浓度及POC与PON比值(C/N)有拮抗性交互作用。在一次性培养后,酸化显著降低了浮游植物群落的沉降速率;而在连续培养后,酸化和N加富使浮游植物群落沉降速率显著升高。这些结果表明酸化和N加富对与近岸浮游植物相关的生物地球化学循环及在不同生长阶段的种群碳沉降存在不同的潜在影响及交互效应。

Response of Tianjin coastal phytoplankton community to ocean acidification and nitrate enrichment

To assess the effects of the coupling of ocean acidification (OA) and eutrophication on the coastal phytoplankton ecosystems, this study mainly investigated the interactive effects of the changes in CO₂ and nitrate concentrations on the biogeochemistry of the phytoplankton community in coastal Tianjin area. Both batch incubation and continuous incubation were conducted under four experimental conditions: 1) control, no nitrate addition, p(CO₂) 40.53 Pa; 2) OA, no nitrate addition, p(CO₂) 101.3 Pa; 3) N addition: nitrate 50 µmol/L, p(CO₂)40.53 Pa; and 4) OA + N addition: nitrate 50 µmol/L, p(CO₂) 101.3 Pa. Our study suggests that nitrate enrichment promoted more accumulation of total chlorophyll biomass, particulate organic carbon (POC), and particulate organic nitrogen (PON) concentrations than OA. Both OA and N enrichment increased the cell size of the phytoplankton community. The results from the continuous incubation experiments suggest that OA and N enrichments had a synergistic interactive effect on Chl a, biogenic silica (BSi) and PON concentrations, PON to particulate organic phosphorous ratio (N/P), POC to BSi ratio (C/BSi), and the sinking rate; however, antagonistic interactive effects were observed on the POP and POC concentrations and POC to PON ratio (C/N). After the batch culture, OA significantly reduced the sinking rate of the phytoplankton community. Nevertheless, OA and N enrichment significantly increased the sinking rate of the phytoplankton community in the continuous culture. These results indicate that acidification and N enrichment might have potential different interactive effects on the biogeochemical cycles associated with coastal phytoplankton and the carbon export of phytoplankton populations at different growth stages.