Microbial mechanisms coupling carbon and phosphorus cycles in phosphorus-limited northern Adriatic Sea

TitleMicrobial mechanisms coupling carbon and phosphorus cycles in phosphorus-limited northern Adriatic Sea
Publication TypeJournal Article
Year of Publication2014
AuthorsMalfatti F., Turk V., Tinta T., Mozetic P., Manganelli M., Samo T.J, Ugalde JA, Kovac N., Stefanelli M., Antonioli M., Fonda-Umani S., Del Negro P., Cataletto B., Hozic A., DeNardis N.I, Zutic V., Svetlicic V., Radic T.M, Radic T., Fuks D., Azam F
JournalScience of the Total Environment
Date Published2014/02
Type of ArticleArticle
ISBN Number0048-9697
Accession NumberWOS:000331415600124
Keywordsalkaline-phosphatase activity; Bacterial alkaline phosphatase; bacterial-growth; dissolved; DOC accumulation; ELF-enzyme; exoenzymatic activities; experiment; gulf-of-trieste; Hydrolyses; Laser Scanning Confocal; marine bacterioplankton; Marine carbon biogeochemistry; mediterranean sea; mesocosm; Microscope; natural aquatic systems; organic-carbon; phytoplankton bloom

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 mu M 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) 131 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. Published by Elsevier B.V.

Short TitleSci. Total Environ.
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