Large variation in growth-limiting factors for marine heterotrophic bacteria in the Arctic waters of Spitsbergen (78 degrees N)

摘要

Growth-limiting factors for heterotrophic bacteria were evaluated in euphotic coastal and fjord waters at 5 stations at Spitsbergen (78 degrees N). The study was done in late summer and comprised measurements of natural concentrations of nutrients, and bioassays in which changes in cell numbers and biomass production were the response variables after the addition of glucose (C), inorganic nitrogen (N; ammonium and nitrate) and inorganic phosphorus (P; phosphate), alone or in combination. The temperature at all 5 stations was similar, and the concentrations of dissolved inorganic N and P were so low that they could limit growth. Concentrations of particulate C, N and P were higher at 2 northernmost stations, indicating higher total biomass and stronger competition between bacteria and phytoplankton. The amendments did not elicit a response in terms of cell numbers, probably due to longer response times or high mortality. For biomass production (leucine incorporation), significant effects of the amendments were observed at 3 out of the 5 stations. Mineral nutrient limitation (N and P) was detected at the 2 high-biomass stations, and carbon limitation was detected once. For the 2 coastal stations, more than 1 limiting factor (dual limitation) was recorded, with C and P as secondary limiting factor. No correlation was found between the species composition of the communities and the response in the bioassays. The spatial variability in the responses of heterotrophic bacteria to the addition of resources within a narrow time window reveals that we have insufficient knowledge to predict the consequences of a scenario in which warming occurs in Arctic areas. This lack of knowledge makes it impossible to predict the type of interaction between heterotrophic bacteria and phototrophs, and thus the implications of warming for food web functionality and stability.