Diel periodicity of bacterioplankton in the euphotic zone of the subtropical Atlantic Ocean

Abstract

We tested the hypothesis that in the euphotic zone of oligotrophic oceanic waters, the growth-limiting nutrients for bacterioplankton vary over a diel cycle due to competition with phytoplankton, leading to distinct diel patterns in bacterioplankton. During a cruise across the subtropical Atlantic Ocean, a distinct diel periodicity in bacterioplankton was detectable, with highest bacterial abundance in the early morning and declining over the day. A peak in the frequency of dividing cells (FDC, 20 to 25% of the total bacterial community) was recorded at midnight; FDC rates were consistently low during the day and cell volume increased over the day until the early night period. No diel variations in these parameters were detectable in the layers below the deep chlorophyll maximum (DCM). Bio-assay experiments with freshly collected, N+P amended water were started in the early morning. No significant bacterial growth was detectable in the early morning while, in the bio-assays that started at noon, significant bacterial growth was detectable in the N+P treatments. P amendment alone also caused an increase in bacterial abundance although to a lesser extent. Thus, we have evidence that the bacterioplankton in the euphotic layer of the subtropical Atlantic are not limited by the availability of N+P in the morning (most likely limited in C) but at noon when they are competing with phytoplankton for the inorganic N+P sources. Based on the concomitantly measured decline in inorganic N+P in the bio-assays, we estimated the C:N:P ratio of newly produced bacteria. The mean atomic C:N:P ratio for the bacteria in the N+P amended bio-assay experiments started in the early morning was C:N:P = 15:13:1 while the corresponding ratio for bacteria in the bio-assays started at noon was C:N:P = 118:11:1. This diel variation in the C:N:P ratio was caused by the 1 order of magnitude higher bacterial C production at noon as compared to the early morning. Thus, excess uptake of N+P occurs during the morning and luxury C uptake during noon. This plasticity in the C:N:P ratio of bacterioplankton might be a strategy to overcome, at least partly, periods of shortage in a specific nutrient species in the oligotrophic subtropical Atlantic. MARINE ECOLOGY PROGRESS SERIES

Contributions of phytoplankton and other particles to inherent optical properties in New England continental shelf waters

“…The highest concentrations of both heterotrophic prokaryotes and eukaryotic phytoplankton occurred in spring surface waters, consistent with a previous suggestion of a link between the abundances of the two microbial groups (Azam et al 1983). Previous studies have documented decreasing bacterial concentrations with depth, as we observed in the spring, and concentrations similar to ours (ϳ10 6 ml Ϫ1 ) have typically been found for the upper ocean (Cho and Azam 1990;Koike et al 1990;Sieracki and Viles 1992;Noble and Fuhrman 1998;Kuipers et al 2000). Unimodal distributions were observed for D in the summer and n in both seasons (Fig.…”

Dissolved organic matter and bacterial production and respiration in the sea‐surface microlayer of the open Atlantic and the western Mediterranean Sea

“…Diel variations of DOC concentrations and bacterial activity in the euphotic zone have been reported for the Mediterranean Sea (Gasol et al 1998) and for bacterial abundance also in the SATL (Kuipers et al 2000). Thus, whenever possible, we sampled in the morning, at noon, and in the late afternoon.…”

Linking diel patterns in community respiration to bacterioplankton in an oligotrophic high‐elevation lake

“…5) where bacterioplankton grown on dusk water had a growth-rate constant over twice as large as bacterioplankton grown on water collected the following dawn. Evidence from the literature suggests this differential response is relatively common; similar diel patterns in bacterial productivity have been observed in rates of cell division (Coffin et al 1993;Kuipers et al 2000) as well as incorporation rates of leucine or thymidine (Straskrabova and Fuksa 1982;Coffin et al 1993;Van Wambeke et al 2009). At the seasonal timescale, the two phases of overnight respiration characterized in Emerald Lake were correlated with different parameters, suggesting control by different mechanisms.…”

“…Most importantly, the mechanisms driving such diel patterns in respiration remain unclear. Similarly, although diel variability in bacterioplankton abundance (BA) and production has been documented repeatedly in marine (Kuipers et al 2000;Van Wambeke et al 2009) and freshwater (Simon 1994;Panzenbö ck 2007) systems, no studies have simultaneously characterized bacterioplankton production or growth rates and variability in respiration rates, providing evidence of a mechanistic link.…”