CO2 fixation by planktonic algae and subsequent assimilation of algae-derived organics by planktonic bacteria, and the coupling relationship between them were studied at elevated CO2 levels. The elevated CO2 levels were achieved in three sets of mesocoms, each having a volume faction of 400×10-6 (P1), 800×10-6 (P2), and 1200×10-6 (P3), respectively. Results showed that elevated CO2 supplies promoted algal growth, leading to biomass of 9.4×106cells/mL, 1.1×107cells/mL, and 1.5×107cells/mL at P1, P2, and P3 levels. Algal esterase activity was also reduced at these CO2 levels, but the time to reach peak biomass was not affected. For planktonic bacteria in the same mesocoms, they reached peak biomass on day 12 (P1), 14 (P2), and 20 (P3), leading to cell density of 2.10×106cells/mL (P1), 1.94×106cells/mL (P2), and 1.70×106cells/mL (P3). In the first seven days, the growth rate of planktonic bacteria correlated with increasing CO2 levels:vP3>vP2>vP1, as was the bacterial activity. At elevated CO2 levels, algae showed high biomass with low metabolic activity, while bacterial showed relative low biomass with high metabolic activity; this contrast reflected differences in the response mechanism of algae and bacteria to changes in CO2levels. Therefore, the high biomass resulting from elevated CO2under global change may not effectively transform into bacterial biomass.%采用控制空气CO2浓度的围隔体系(P1：400×10-6体积分数,下同,P2：800×10-6,P3：1200×10-6),在不同空气CO2浓度条件下,分析水华微囊藻对 CO2的同化作用和异养细菌对藻源性有机碳的异化作用,以及二者出峰时间耦合关系的变化.结果表明,CO2浓度升高能够促进水华微囊藻的生长,P1、P2和P3条件下藻的数量分别达9.4×106,1.1×107,1.5×107cells/mL.同时高浓度CO2降低了藻细胞内酯酶活性但并未影响藻达到峰值所需时间.在不同 CO2浓度水平下,浮游细菌达到峰值的时间顺序是 P1(12d)vP2>vP1,细菌活性是P3>P2>P1.高CO2浓度条件下,浮游藻类呈现高生物量和低活性的状态,而浮游细菌呈现低生物量和高活性的状态,反映出 CO2浓度的改变对同化和异化作用不同的影响机制.因此,CO2浓度升高后导致的浮游藻类生物量的积累可能无法通过促进浮游细菌的生长达到有效转化.
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