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17 pages, 9 figures, 2 tables, supplementary material https://www.frontiersin.org/articles/10.3389/fmars.2021.683354/full#supplementary-material.-- Data Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation ; Particulate organic matter (POM) lability is one of the key factors determining the residence time of organic carbon (OC) in the marine system. Phytoplankton community composition can influence the rate at which heterotrophic microorganisms decompose phytoplankton detrital particles and thus, it controls the fraction of OC that reaches the ocean depths, where it can be sequestered for climate-relevant spans of time. Here, we compared the degradation dynamics of POM from phytoplankton assemblages of contrasting diatom dominance in the presence of mesopelagic prokaryotic communities during a 19-day degradation experiment. We found that diatom-derived POM exhibited an exponential decay rate approximately three times lower than that derived from a community dominated by flagellated phytoplankton (mainly coccolithophores and nanoflagellates). Additionally, dissolved organic matter (DOM) released during the degradation of diatom particles accumulated over the experiment, whereas only residual increases in DOM were detected during the degradation of non-diatom materials. These results suggest that diatom-dominance enhances the efficiencies of the biological carbon pump and microbial carbon pump through the relatively reduced labilities of diatom particles and of the dissolved materials that arise from their microbial processing ; This research was funded by projects SUAVE (CTM2014-54926-R), ANIMA (CTM2015-65720-R), and BIOGAPS (CTM2016-81008-R) and the institutional support of the "Severo Ochoa Centre of Excellence" accreditation (CEX2019-000928-S) from the Spanish government. MC-B was supported by a FPU pre-doctoral contract (FPU16/01925) from the Spanish government. We acknowledge support for the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI) ; Peer reviewed

International audience ; Sediment trap particles, as well as particulate organic material including particles larger than 10 pn coiiected by in situ pumps (ISP) and fresh corpses of the gelatinous zoopIankton species Thalia democratica, were coiiected in the northwestern Mediterranean Sea from Apnl to July 1995, and incubated (after mixing with 0.2 pn filtered seawater) under laboratory conditions with their own bac-tenal assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 p n) and colloidal(0.02 < COC < 0.7 pm) organic carbon contents, as weil as bactenal abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaned with an increase in bactenal abundance and production, bactena being the main mediators of particle decomposition. We found that COC accounted for 19 to 31 % of DOC immediately after particle dilution in 0.2 pm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids compnsed less than 7 % of DOC in the 0.2 pn filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bactenal populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO2 through bacterial respiration. The results showed that bactena degraded 16 to 87 % of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both 1SP-and trap particles are composed of 2 labile and 1 refractory organic fraction. A lG-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce ...

International audience ; Sediment trap particles, as well as particulate organic material including particles larger than 10 pn coiiected by in situ pumps (ISP) and fresh corpses of the gelatinous zoopIankton species Thalia democratica, were coiiected in the northwestern Mediterranean Sea from Apnl to July 1995, and incubated (after mixing with 0.2 pn filtered seawater) under laboratory conditions with their own bac-tenal assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 p n) and colloidal(0.02 < COC < 0.7 pm) organic carbon contents, as weil as bactenal abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaned with an increase in bactenal abundance and production, bactena being the main mediators of particle decomposition. We found that COC accounted for 19 to 31 % of DOC immediately after particle dilution in 0.2 pm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids compnsed less than 7 % of DOC in the 0.2 pn filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bactenal populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO2 through bacterial respiration. The results showed that bactena degraded 16 to 87 % of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both 1SP-and trap particles are composed of 2 labile and 1 refractory organic fraction. A lG-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce ...

International audience ; Sediment trap particles, as well as particulate organic material including particles larger than 10 pn coiiected by in situ pumps (ISP) and fresh corpses of the gelatinous zoopIankton species Thalia democratica, were coiiected in the northwestern Mediterranean Sea from Apnl to July 1995, and incubated (after mixing with 0.2 pn filtered seawater) under laboratory conditions with their own bac-tenal assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 p n) and colloidal(0.02 < COC < 0.7 pm) organic carbon contents, as weil as bactenal abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaned with an increase in bactenal abundance and production, bactena being the main mediators of particle decomposition. We found that COC accounted for 19 to 31 % of DOC immediately after particle dilution in 0.2 pm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids compnsed less than 7 % of DOC in the 0.2 pn filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bactenal populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO2 through bacterial respiration. The results showed that bactena degraded 16 to 87 % of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both 1SP-and trap particles are composed of 2 labile and 1 refractory organic fraction. A lG-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce the data sets.

International audience ; Sediment trap particles, as well as particulate organic material including particles larger than 10 pn coiiected by in situ pumps (ISP) and fresh corpses of the gelatinous zoopIankton species Thalia democratica, were coiiected in the northwestern Mediterranean Sea from Apnl to July 1995, and incubated (after mixing with 0.2 pn filtered seawater) under laboratory conditions with their own bac-tenal assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 p n) and colloidal(0.02 < COC < 0.7 pm) organic carbon contents, as weil as bactenal abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaned with an increase in bactenal abundance and production, bactena being the main mediators of particle decomposition. We found that COC accounted for 19 to 31 % of DOC immediately after particle dilution in 0.2 pm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids compnsed less than 7 % of DOC in the 0.2 pn filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bactenal populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO2 through bacterial respiration. The results showed that bactena degraded 16 to 87 % of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both 1SP-and trap particles are composed of 2 labile and 1 refractory organic fraction. A lG-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce the data sets.

International audience Sediment trap particles, as well as particulate organic material including particles larger than 10 pn coiiected by in situ pumps (ISP) and fresh corpses of the gelatinous zoopIankton species Thalia democratica, were coiiected in the northwestern Mediterranean Sea from Apnl to July 1995, and incubated (after mixing with 0.2 pn filtered seawater) under laboratory conditions with their own bac-tenal assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 p n) and colloidal(0.02 < COC < 0.7 pm) organic carbon contents, as weil as bactenal abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaned with an increase in bactenal abundance and production, bactena being the main mediators of particle decomposition. We found that COC accounted for 19 to 31 % of DOC immediately after particle dilution in 0.2 pm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids compnsed less than 7 % of DOC in the 0.2 pn filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bactenal populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO2 through bacterial respiration. The results showed that bactena degraded 16 to 87 % of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both 1SP-and trap particles are composed of 2 labile and 1 refractory organic fraction. A lG-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce the ...