Uppsala University, Institute of Limnology, Box 557, S-751 22 Uppsala, Sweden.
Appl Environ Microbiol. 1992 Sep;58(9):2938-47. doi: 10.1128/aem.58.9.2938-2947.1992.
The molecular size distribution and biochemical composition of the dissolved organic carbon released from natural communities of lake phytoplankton (photosynthetically produced dissolved organic carbon [PDOC]) and subsequently used by heterotrophic bacteria were determined in three lakes differing in trophic status and concentration of humic substances. After incubation of epilimnetic lake water samples with HCO(3) over one diel cycle, the phytoplankton were removed by size-selective filtration. The filtrates, still containing most of the heterotrophic bacteria, were reincubated in darkness (heterotrophic incubation). Differences in the amount and composition of PDOC between samples collected before the heterotrophic incubation and samples collected afterwards were considered to be a result of bacterial utilization. The PDOC collected at the start of the heterotrophic incubations always contained both high (>10,000)- and low (<1,000)-molecular-weight (MW) components and sometimes contained intermediate-MW components as well. In general, bacterial turnover rates of the low-MW components were fairly rapid, whereas the high-MW components were utilized slowly or not at all. In the humic lake, the intermediate-MW components accounted for a large proportion of the net PDOC and were subject to rapid bacterial utilization. This fraction probably consisted almost entirely of polysaccharides of ca. 6,000 MW. Amino acids and peptides, other organic acids, and carbohydrates could all be quantitatively important parts of the low-MW PDOC that was utilized by the heterotrophic bacteria, but the relative contributions of these fractions differed widely. It was concluded that, generally, low-MW components of PDOC are quantitatively much more important to the bacteria than are high-MW components, that PDOC released from phytoplankton does not contain substances of quantitative importance as bacterial substrates in all situations, and that high-MW components of PDOC probably contribute to the buildup of refractory, high-MW dissolved organic carbon in pelagic environments.
从富营养化和腐殖质浓度不同的三个湖泊中的浮游植物群落（光合作用产生的溶解有机碳 [PDOC]）中释放的溶解有机碳的分子大小分布和生化组成，以及随后被异养细菌利用的情况，进行了确定。在光照条件下，用 HCO(3)对湖泊上层水样品进行了为期一个昼夜的培养后，通过尺寸选择过滤去除浮游植物。仍然含有大多数异养细菌的滤出液在黑暗中再次培养（异养培养）。在异养培养之前和之后收集的样品之间 PDOC 的数量和组成的差异被认为是细菌利用的结果。在异养培养开始时收集的 PDOC 总是包含高（> 10,000）和低（< 1,000）分子量（MW）的成分，有时也包含中等 MW 的成分。一般来说，低 MW 成分的细菌周转率相当快，而高 MW 成分则利用缓慢或根本不利用。在富营养化湖泊中，中等 MW 成分占净 PDOC 的很大比例，并迅速被细菌利用。这部分可能几乎完全由约 6,000 MW 的多糖组成。氨基酸和肽、其他有机酸和碳水化合物都可能是异养细菌利用的低 MW PDOC 的重要组成部分，但这些部分的相对贡献差异很大。结论是，一般来说，PDOC 的低 MW 成分对细菌的重要性远远超过高 MW 成分，从浮游植物释放的 PDOC 并不总是包含在所有情况下作为细菌底物具有定量重要性的物质，并且 PDOC 的高 MW 成分可能有助于在浮游环境中形成难降解的高 MW 溶解有机碳。
