Synchronous shifts in dissolved organic carbon bioavailability and bacterial community responses over the course of an upwelling-driven phytoplankton bloom

Abstract

Interactions between dissolved organic carbon (DOC) and bacterioplankton were examined during a diatom and Phaeocystis bloom in the Santa Barbara Channel (SBC) over five days following an upwelling event.The SBC was heterogeneous in physical state (recently upwelled vs. more stratified), nutrient concentration, and productivity, encompassing phytoplankton physiological states from a healthy bloom through the onset of silicon stress. DOC accumulated in the upper 10 m over the bloom, with compositional shifts indicated by chromophoric dissolved organic matter (CDOM) parameters. DOC bioavailability and bacterial growth and community composition responses were assessed with dilution batch-culture bioassays. In these experiments, bacterioplankton DOC usage increased over the bloom, with uptake of 1.5-5.3 lmol L 21 over three days, 1.5-5.7 lmol L 21 over one week, and 1.8-10.8 lmol L 21 over 10 weeks. DOC removal was poorly correlated with traditional proxies of bioavailability (chlorophyll a concentration, elemental ratios of dissolved organic matter, and CDOM). However, bacterial growth efficiency (BGE) was strongly related to in situ conditions, with higher BGEs on fresher, late-bloom DOC. After 10 weeks, 1.6-15.7 lmol L 21 of the DOC that accumulated during the bloom remained unutilized in the bioassays, with higher concentrations of persistent DOC in experiments from senescent bloom physiological states, supporting the putative relationship between phytoplankton blooms and seasonal DOC accumulation in the field. These experiments demonstrate that DOC released by the plankton community during a bloom fuels increased short-term and long-term bacterial activity, enhances presumed trophic transfer via increased BGEs, and leads to the accumulation of persistent, potentially exportable, DOC. V C 2015 Association for the Sciences of Limnology and Oceanography

Cascading influence of inorganic nitrogen sources on DOM production, composition, lability and microbial community structure in the open ocean

“…Moreover, these taxa dominated community structure in all samples (control and N enriched treatments), emphasizing that the induced production of organic matter did not generate a drastic shift in community structure, only subtle (but significant) enrichment of selected taxa. Many of the taxa enriched by nitrogen additions here are consistent with those enriched in natural and nutrient‐induced phytoplankton blooms, including widespread observations of Flavobacteria and Roseobacter enrichment (Teeling et al ., ; Buchan et al ., ; Nelson et al ., ; Wear et al ., ; Landa et al ., ; Shilova et al ., ) but also enrichment in Actinobacteria OM1/OCS155 and Gammaproteobacteria SAR86 as observed in subtropical mesoscale eddies (Nelson et al ., ), enrichment in copiotrophic Alteromonadaceae and Oceanospirillaceae observed in both coastal upwelling blooms (Wear et al ., ) and subtropical gyre nitrogen additions (Shilova et al ., ), and enrichments in oligotrophic Gammaproteobacterial clades (OM60/NOR5, SAR92, KI89A) variously documented in both upwelling (Teeling et al ., ; Wear et al ., ) and Southern Ocean iron enrichments (Landa et al ., ). The growth of Flavobacteria under N enrichment may be associated with the stimulation of phytoplankton growth (Fig.…”

“…During dark remineralization the rapid (∼1 d) growth of gammaproteobacterial copiotrophs in the Alteromonadaceae and Oceanospirillaceae is consistent with previous studies (Lauro et al ., ; Nelson and Carlson, ; Nelson and Wear, ; Wear et al ., ,b) and supports a view of these copiotrophs as ecologically relevant ‘first responders’ to the availability of labile DOM in the absence of grazing (Pedler et al ., ). Rhodobacteraceae (including members of the widely studied Roseobacter clades) were most enriched on and ∼1 week DOM remineralization, trends that correspond to their perceived role as opportunistic and relatively slow growing copiotrophs (Nelson and Carlson, ; Wear et al ., ,b) that thrive on the products of other microbial consortia (Wagner‐Döbler and Biebl, ; Luo et al ., ; Nelson and Carlson, ; Sarmento et al ., ; Buchan et al ., ). Notably, the clades of Rhodobacteraceae that were enriched on ‐amended and N‐DOM amendments were different, suggesting some parsing of ecological niche space between inorganic and organic nutrient specialists.…”

“…The oceanic DOM pool is the largest pool of reduced carbon (C) (662 ± 32 pg C) in the ocean (Hansell et al ., ) and is extremely diverse in chemical composition and structure (Repeta, ). DOM composition and reactivity varies in time and space (Goldberg et al, ; Hansell, ) and can be a function of the DOM source (Nelson and Carlson, ; Becker et al ., ; Wear et al ., ,b) and the extent of alteration by heterotrophic and abiotic processes (Kujawinski, ; Carlson and Hansell, ). How nutrient availability affects the production and consumption of DOM is a key area of current research (Carlson and Hansell, ).…”

Primer selection impacts specific population abundances but not community dynamics in a monthly time‐series 16S rRNA gene amplicon analysis of coastal marine bacterioplankton

“…Samples were collected from the Santa Barbara Channel, CA, USA, either on the Plumes and Blooms time‐series cruise program (Catlett and Siegel, ) or from a process cruise during a strong diatom and Phaeocystis bloom (University‐National Oceanographic Laboratory Systems cruise PS1103; Wear et al ., ). This coastal site is characterized by upwelling‐driven phytoplankton blooms (Otero and Siegel, ), leading to a seasonal enrichment in copiotrophic bacterioplankton (Wear et al ., ). These blooms are followed by a lengthy period of stratification (Otero and Siegel, ), which, along with a Mediterranean climate that minimizes terrestrial inputs, results in more oligotrophic conditions than are typical for coastal systems.…”

Transcriptional Control in Marine Copiotrophic and Oligotrophic Bacteria with Streamlined Genomes

“…These laboratory studies have typically examined copiotrophic bacteria isolated and grown using high concentrations of organic substrates (1)(2)(3). Although possible during phytoplankton blooms and in particles (4,5), such high concentrations are not common, so copiotrophic bacteria are much less abundant than oligotrophic bacteria (6). In most of the ocean, concentrations of organic compounds and inorganic nutrients are very low and impose strong selective pressure for oligotrophic bacteria (6).…”