海水中藻菌共培养体系对碳氮磷的吸收转化

Uptake and transformation of carbon,nitrogen and phosphorus in the co-culture system of algae and bacteria in seawater

海洋环境中,细菌和微藻之间的物质交换是生源要素在自然界中迁移转化的重要方式。为进一步了解生源要素的生物地球化学循环,在实验室模拟条件下,研究了共培养体系中营养盐和有机物在细菌和微藻之间的转换。通过纯培养中肋骨条藻(Skeletonema costatum)、东海原甲藻(Prorocentrum donghaiense)、天然海水中的细菌以及藻菌混合培养,分析了营养盐和有机物随藻菌生物量的变化情况,并计算了溶解有机碳(DOC)和溶解有机氮(DON)的浓度比值[(DOC/DON)a]。结果发现,在共培养体系中,细菌对中肋骨条藻的生长有抑制作用,对东海原甲藻影响不明显;中肋骨条藻有利于细菌生长,东海原甲藻抑制细菌生长,这种不同可能与微藻的粒径有关。海洋细菌在2种藻的指数生长均期均会促进微藻吸收氨氮(NH_4-N),但在生长末期NH_4-N以释放为主。硝氮(NO_3-N)的浓度与藻的生长呈负相关,但在衰亡期NO_3-N略有增加,表明NO_3-N再生所需时间较长。细菌对硝氮的吸收量较少,但对其再生有贡献。细菌和中肋骨条藻对磷酸盐(PO_4-P)的吸收存在竞争,但与东海原甲藻的竞争关系不明显。不同培养体系中DOC浓度变化不同,在藻菌共培养体系中增加较快,纯藻培养体系中增加缓慢,在纯菌培养体系中缓慢减少。通过对DOC与DON浓度比值的分析,发现用判断颗粒有机碳(POC)来源的方法可以分析DOC的来源。

In the marine environment, the exchange of the substance between bacteria and algae is an important way of the migration and transformation of biogenic elements in the natural world. In order to obtain a further understanding of the biogeochemical cycles of biogenic elements, the transformation of nutrients （ nitrogen and phosphorus） and organic matter between marine bacteria and two types of algae （ Skeletonema costatum and Prorocentrum donghaiense） were studied in a co- culture or single-culture system of algae and bacteria based on a laboratory-simulated experiment. The changes of nutrient and organic carbon were tracked and the biomass of bacteria and the two algae were calculated. In addition, the concentration ratio [ （ DOC/DON）, ] of dissolved organic carbon （DOC） to dissolved organic nitrogen （DON） in different culture systems was analyzed to determine the sources of organic matter. The results indicated that bacteria may inhibit the growth of S. costatum, but have little effects on growth of P. donghaiense in the co-culture system. On the contratry, S. costatum accelerated the growth of bacteria, whereas P. donghaiense suppressed the growth of bacteria, which is probably related to the different sizes of the two algae. During the exponential growth phase of the two algae, bacteria promoted the uptake of ammonia （ NH4-N） by the algae, however NH4-N was mainly released at the end stage of algae growth. The concentrations of nitrate （ NO3-N） and the biomass of algae showed a nearly negative correlation, but NO3-N increased slightly during the decline phase of algae, indicating that the regeneration of NO3-N took a longer time. Bacteria uptook little NO3-N, but contributed to the regeneration of NO3-N. Bacteria and S. costatum competed for phosphate （PO4-P） and bacteria affected the uptake of PO4-P by S. costatum. There were not obvious different between concentrations of PQ-P in co-culture of P. donghaiense and bacteria from that in single culture of P. donghaiense, which was in contrast to the results of the culture with S. costatum. In the course of the culture, the concentration of DOC varied in different cultural systems. DOC increased rapidly in the co-culture systems of bacteria and algae, whereas the concentration of DOC increased slowly in the pure algal systems, and decreased slowly in the single-culture bacterial system. The analysis of the concentration ratio of DOC and DON showed that the method of tracing the source of particulate organic carbon （POC） can also be used to trace the source of DOC.