Dominance of facultative and obligate oligotrophic bacteria in surface waters above Gunnerus and Astrid Ridge, Antarctic Ocean

Facultative and obligate oligotrophs have been enumerated in March/April 1990 by the MPN-method with 14C-protein hydrolysate as tracer substrate. Obligate (10-3360 cells/ml) and facultative (110-9000 cells/ml) oligotrophs revealed to be the dominant population above Gunnerus Ridge (65°30'-68°S; 31-35°E) at a depth of 25 m compared with eutrophic bacteria (5 to 260 CFU/ml). Above Astrid Ridge (65-68°S; 8-18°E), obligate (0-1100 cells/ml) and facultative oligotrophs (300-9000 cells/ml) were also abundant but not always dominant. Bacterial biomass above Gunnerus Ridge was only between 7.3 and 43.6% of particulate biomass, but biomass of bacteria above Astrid Ridge amounted from 56.9 to >100% of particulate biomass; an exception was station no. PS16/552 with only 22.2% of bacterial biomass. Ratio of bacterial biomass to particulate biomass was negatively correlated with maximal primary production, complementing the view that phytoplankton was the dominant population above Gunnerus Ridge, whereas bacteria predominated above Astrid Ridge. Eutrophic bacteria were also more abundant above Astrid Ridge, with 3 to 6380 CFU/ml. Total bacteria by acridine orange direct counts amounted from 1 x 10**4 to 34.2 x 10**4 cells/ml. Bacterial biomass above Gunnerus Ridge was 1.8 to 10.7, and above Astrid Ridge 5.7 to 13.6 mg C/m*3. Maximal primary production above Gunnerus Ridge was 4.5 to 11.0, and above Astrid Ridge 2.3 to 3.5 mg C/m**3/d.1990年3月与4月期间，研究人员采用以¹⁴C标记蛋白水解物为示踪底物的最大概率计数法（MPN-method），对兼性与专性寡营养菌（oligotrophs）进行了计数。在古纳勒斯海岭（65°30′—68°S；31°—35°E）上方25米水深处，专性寡营养菌（10~3360 cells/ml）与兼性寡营养菌（110~9000 cells/ml）为优势菌群，其丰度显著高于富营养细菌（5~260 CFU/ml）。 在阿斯特里德海岭（65°—68°S；8°—18°E）上方，专性寡营养菌（0~1100 cells/ml）与兼性寡营养菌（300~9000 cells/ml）同样丰度较高，但并非始终占据主导地位。 古纳勒斯海岭上方的细菌生物量仅占颗粒生物量的7.3%~43.6%，但阿斯特里德海岭上方的细菌生物量占颗粒生物量的比例为56.9%~>100%；仅PS16/552号站位为例外，其细菌生物量占比仅为22.2%。 细菌生物量与颗粒生物量的比值与最大初级生产力呈负相关，这一结果佐证了如下观点：古纳勒斯海岭上方的优势类群为浮游植物（phytoplankton），而阿斯特里德海岭上方则以细菌占主导。 阿斯特里德海岭上方的富营养细菌丰度同样更高，可达3~6380 CFU/ml。通过吖啶橙直接计数法（acridine orange direct counts）测得的总细菌丰度为1×10⁴~34.2×10⁴ cells/ml。 古纳勒斯海岭上方的细菌生物量为1.8~10.7 mg C/m³，阿斯特里德海岭上方则为5.7~13.6 mg C/m³。 古纳勒斯海岭上方的最大初级生产力为4.5~11.0 mg C/(m³·d)，阿斯特里德海岭上方则为2.3~3.5 mg C/(m³·d)。