Factors controlling the seasonality of bacterial carbon flux in a coastal marine system

ALONSO-SÁEZ, L.; VÁZQUEZ-DOMÍNGUEZ, E.; CARDELÚS, C.; PINHASSI, J.; SALA, M. M.; LEKUNBERRI, I.; BALAGUÉ, V.; VILA-COSTA, M.; UNREIN, F.; MASSANA, R.; SIMÓ, R.; GASOL, J. M.

ECOSYSTEMS (NEW YORK. PRINT)

Springer

Año: 2008 vol. 11 p. 397 - 409

1432-9840

Data from several years of monthly samplings arecombined with a 1-year detailed study of carbonflux through bacteria at a NW Mediterraneancoastal site to delineate the bacterial role in carbonuse and to assess whether environmental factors orbacterial assemblage composition affected the insitu rates of bacterial carbon processing. Leucine(Leu) uptake rates [as an estimate of bacterialheterotrophic production (BHP)] showed highinterannual variability but, on average, lower valueswere found in winter (around 50 pM Leu)1h)1) as compared to summer (around 150 pMLeu)1 h)1). Leu-to-carbon conversion factors rangedfrom 0.9 to 3.6 kgC mol Leu)1, with generallyhigher values in winter. Leu uptake was onlyweakly correlated to temperature, and over a fullyearcycle (in 2003), Leu uptake peaked concomitantlywith winter chlorophyll a (Chl a) maxima,and in periods of high ectoenzyme activities inspring and summer. This suggests that both lowmolecular weight dissolved organic matter (DOM) released by phytoplankton, and high molecularweight DOM in periods of low Chl a, can enhanceBHP. Bacterial respiration (BR, range 7–48 lg Cl)1 d)1) was not correlated to BHP or temperature,but was significantly correlated to DOC concentration.Total bacterial carbon demand (BHP plusBR) was only met by dissolved organic carbonproduced by phytoplankton during the winterperiod. We measured bacterial growth efficienciesby the short-term and the long-term methods andthey ranged from 3 to 42%, increasing during thephytoplankton blooms in winter (during the Chl apeaks), and in spring. Changes in bacterioplanktonassemblage structure (as depicted by denaturinggradient gel electrophoresis fingerprinting) werenot coupled to changes in ecosystem functioning,at least in bacterial carbon use.