Response of Nodularia spumigena to pCO2 – Part 3: Turnover of phosphorus compounds

[摘要] Diazotrophic cyanobacteria form extensive summer blooms in the Baltic Seadriving the surrounding surface waters into phosphate limitation. One of themain bloom-forming species is the heterocystous cyanobacterium Nodularia spumigena. N. spumigena exhibitsaccelerated uptake of phosphate through the release of the extracellularenzyme alkaline phosphatase whose activity also serves as an indicator ofthe hydrolysis of dissolved organic phosphorus (DOP). The present studyinvestigated the utilisation of DOP and its compounds (e.g., ATP) by N. spumigena duringgrowth under different CO₂ concentrations, in order to estimatepotential consequences of ocean acidification on the cell's supply withphosphorus (P). Cell growth, the phosphorus pool, and four DOP compounds (ATP,DNA, RNA, and phospholipids) were determined in three setups with differentCO₂ concentrations (average 341 μatm, 399 μatm, and508 μatm) during a 15-day batch experiment. The results showed stimulatedgrowth of N. spumigena and a rapid depletion of dissolved inorganic phosphorus (DIP) inall pCO₂ treatments. DOP uptake was enhanced by a factor of 1.32 at 399 μatm and of 2.25 at 508 μatm compared to the lowest CO₂concentration. Among the measured DOP compounds, none was found toaccumulate preferentially during the incubation or in response to a specificpCO₂ treatment. However, at the beginning 61.9 ± 4.3% of totalDOP were not characterised but comprised the most utilised fraction. This isdemonstrated by the decrement of this fraction to 27.4 ± 9.9% oftotal DOP during the growth phase with a preference at high pCO₂. Ourresults indicate a stimulated growth of diazotrophic cyanobacteria atincreasing CO₂ concentrations which is accompanied by increasingutilisation of DOP as an alternative P source.

[学科分类] 地球化学与岩石