title: Microbial mechanisms coupling carbon and phosphorus cycles in phosphorus-limited northern Adriatic Sea.
abstract: The coastal northern Adriatic Sea receives pulsed inputs of riverine nutrients, causing phytoplankton blooms and seasonally sustained dissolved organic carbon (DOC) accumulation-hypothesized to cause episodes of massive mucilage. The underlying mechanisms regulating P and C cycles and their coupling are unclear. Extensive biogeochemical parameters, processes and community composition were measured in a 64-day mesocosms deployed off Piran, Slovenia. We followed the temporal trends of C and P fluxes in P-enriched (P+) and unenriched (P-) mesocosms. An intense diatom bloom developed then crashed; however, substantial primary production was maintained throughout, supported by tightly coupled P regeneration by bacteria and phytoplankton. Results provide novel insights on post-bloom C and P dynamics and mechanisms. 1) Post-bloom DOC accumulation to 186 μM remained elevated despite high bacterial carbon demand. Presumably, a large part of DOC accumulated due to the bacterial ectohydrolytic processing of primary productivity that adventitiously generated slow-to-degrade DOC; 2) bacteria heavily colonized post-bloom diatom aggregates, rendering them microscale hotspots of P regeneration due to locally intense bacterial ectohydrolase activities; 3) Pi turnover was rapid thus suggesting high P flux through the DOP pool (dissolved organic phosphorus) turnover; 4) Alpha- and Gamma-proteobacteria dominated the bacterial communities despite great differences of C and P pools and fluxes in both mesocosms. However, minor taxa showed dramatic changes in community compositions. Major OTUs were presumably generalists adapted to diverse productivity regimes.We suggest that variation in bacterial ectohydrolase activities on aggregates, regulating the rates of POM→DOM transition as well as dissolved polymer hydrolysis, could become a bottleneck in P regeneration. This could be another regulatory step, in addition to APase, in the microbial regulation of P cycle and the coupling between C and P cycles.
authors.affiliation: Scripps Institution of Oceanography, University California San Diego, 92037 La Jolla, USA.
authors.forename: F
authors.initials: F
authors.lastname: Malfatti
authors.affiliation: National Institute of Biology, Marine Station Piran, 66330 Piran, Slovenia.
authors.forename: V
authors.initials: V
authors.lastname: Turk
authors.affiliation: National Institute of Biology, Marine Station Piran, 66330 Piran, Slovenia.
authors.forename: T
authors.initials: T
authors.lastname: Tinta
authors.affiliation: National Institute of Biology, Marine Station Piran, 66330 Piran, Slovenia.
authors.forename: P
authors.initials: P
authors.lastname: Mozetič
authors.affiliation: Istituto Superiore per la Prevenzione e la Sicurezza del Lavoro (ISPESL), DIPIA, 00040 Monteporzio Catone, Roma, Italy; Istituto Superiore di Sanità, Dept. of Environment and Primary Prevention, Roma, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Manganelli
authors.affiliation: Scripps Institution of Oceanography, University California San Diego, 92037 La Jolla, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Samo
authors.affiliation: Scripps Institution of Oceanography, University California San Diego, 92037 La Jolla, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Ugalde
authors.affiliation: National Institute of Biology, Marine Station Piran, 66330 Piran, Slovenia.
authors.forename: N
authors.initials: N
authors.lastname: Kovač
authors.affiliation: Istituto Superiore per la Prevenzione e la Sicurezza del Lavoro (ISPESL), DIPIA, 00040 Monteporzio Catone, Roma, Italy; Istituto Superiore di Sanità, Dept. of Environment and Primary Prevention, Roma, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Stefanelli
authors.affiliation: Universita' degli Studi di Trieste, Dipartimento di Biologia, 34127 Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Antonioli
authors.affiliation: Universita' degli Studi di Trieste, Dipartimento di Biologia, 34127 Trieste, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Fonda-Umani
authors.affiliation: Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Sezione Bio, 34151 Santa Croce, Trieste, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Del Negro
authors.affiliation: Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Sezione Bio, 34151 Santa Croce, Trieste, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Cataletto
authors.affiliation: Ruđer Bošković Institute, Division for Marine and Environmental Research, 10000 Zagreb, Croatia.
authors.forename: A
authors.initials: A
authors.lastname: Hozić
authors.affiliation: Ruđer Bošković Institute, Division for Marine and Environmental Research, 10000 Zagreb, Croatia.
authors.forename: N
authors.initials: N
authors.lastname: Ivošević Denardis
authors.affiliation: Ruđer Bošković Institute, Division for Marine and Environmental Research, 10000 Zagreb, Croatia.
authors.forename: V
authors.initials: V
authors.lastname: Zutić
authors.affiliation: Ruđer Bošković Institute, Division for Marine and Environmental Research, 10000 Zagreb, Croatia.
authors.forename: V
authors.initials: V
authors.lastname: Svetličić
authors.affiliation: Ruđer Bošković Institute, Division for Marine and Environmental Research, 10000 Zagreb, Croatia.
authors.forename: T
authors.initials: T
authors.lastname: Mišić Radić
authors.affiliation: Institute for Adriatic Crops and Karst Reclamation, Split, Croatia.
authors.forename: T
authors.initials: T
authors.lastname: Radić
authors.affiliation: Ruđer Bošković Institute, Center for Marine Research, Rovinj, Croatia.
authors.forename: D
authors.initials: D
authors.lastname: Fuks
authors.affiliation: Scripps Institution of Oceanography, University California San Diego, 92037 La Jolla, USA.
authors.forename: F
authors.initials: F
authors.lastname: Azam
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism*; D057486:Carbon Cycle; D055669:Ecological and Environmental Phenomena; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D012623:Seawater / Q000737:chemistry / Q000382:microbiology*; D017524:Slovenia; D014871:Water Microbiology
chemical_list: D010758:Phosphorus; D002244:Carbon
keywords: Bacterial alkaline phosphatase; DOC accumulation; ELF-enzyme; Hydrolyses; Laser Scanning Confocal Microscope; Marine carbon biogeochemistry