Limitation of bacterial growth by dissolved organic matter in the subarctic Pacific

Abstract

To determine if dissolved organic matter (DOM) limits biomass production of heterotrophlc bacterioplankton in the subarctic Pacific, the effect of various DOM and ammonium additions on bacterial production ( 3 ~-t h y n ~l d i n e and '4C-leucine incorporation) and bacterial abundance was examined.Addition of dissolved free amlno acids (DFAA) consistently stimulated 3 ~-t h y m i d i n e incorporation from 31 to 393 % con~pared with unamended controls.Addition of glucose or glucose plus ammonium sometimes stimulated bacterial production, but the effect was always less than that due to DFAA additions A mixture of alkylamines either had no effect or stimulated 3 ~-t h y m i d i n e and 14C-leucine incorporahon to a lesser extent than the DFAA adhtion.Bacterial abundance did not vary significantly during incubatlons, nor were there any differences between treatments, indicating that DFAA add~tions stimulated the average growth rate of the bacterial assemblage.Bactenal growth appeared to b e Chmited, sometimes, since glucose alone stimulated 3H-thynlldine and '4C-leucine in 2 out of 7 expenments.The much greater stimulation of bactenal production by DFAA than by glucose plus ammonium indicated that heterotrophic bacteria in the subarctic Pacific were usually energy-limited.