Contrasted Saharan dust events in LNLC environments: impact on nutrient dynamics and primary production

The response of the phytoplanktonic community (primary production and algal biomass) to contrasted Saharan dust events (wet and dry deposition) was studied in the framework of the DUNE ("a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem") project. We simulated realistic dust deposition events (10 gm(-2)) into large mesocosms (52m(3)). Three distinct dust addition experiments were conducted in June 2008 (DUNE-1-P: simulation of a wet deposition; DUNE-1-Q: simulation of a dry deposition) and 2010 (DUNE-2-R1 and DUNE-2-R2: simulation of two successive wet depositions) in the northwestern oligotrophic Mediterranean Sea. No changes in primary production (PP) and chlorophyll a concentrations (Chl a) were observed after a dry deposition event, while a wet deposition event resulted in a rapid (24 h after dust addition), strong (up to 2.4-fold) and long (at least a week in duration) increase in PP and Chl a. We show that, in addition to being a source of dissolved inorganic phosphorus (DIP), simulated wet deposition events were also a significant source of nitrate (NO3-) (net increases up to +9.8 mu M NO3- at 0.1m in depth) to the nutrient-depleted surface waters, due to cloud processes and mixing with anthropogenic species such as HNO3. The dry deposition event was shown to be a negligible source of NO3-. By transiently increasing DIP and NO3- concentrations in N-P starved surface waters, wet deposition of Saharan dust was able to relieve the potential N or NP co-limitation of the phytoplanktonic activity. Due to the higher input of NO3- relative to DIP, and taking into account the stimulation of the biological activity, a wet deposition event resulted in a strong increase in the NO3-/DIP ratio, from initially less than 6, to over 150 at the end of the DUNE-2-R1 experiment, suggesting a switch from an initial N or NP co-limitation towards a severe P limitation. We also show that the contribution of new production to PP strongly increased after wet dust deposition events, from initially 15% to 60-70% 24 h after seeding, indicating a switch from a regenerated-production based system to a new-production based system. DUNE experiments show that wet and dry dust deposition events induce contrasting responses of the phytoplanktonic community due to differences in the atmospheric supply of bioavailable new nutrients. Our results from original mesocosm experiments demonstrate that atmospheric dust wet deposition greatly influences primary productivity and algal biomass in LNLC environments through changes in the nutrient stocks, and alters the NO3-/DIP ratio, leading to a switch in the nutrient limitation of the phytoplanktonic activity

Contrasted Saharan dust events in LNLC environments: impact on nutrient dynamics and primary production

International audienceThe response of the phytoplanktonic community (primary production and algal biomass) to contrasted Sa-haran dust events (wet and dry deposition) was studied in the framework of the DUNE ("a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem") project. We simu-lated realistic dust deposition events (10 g m −2) into large mesocosms (52 m 3). Three distinct dust addition experiments were conducted in June 2008 (DUNE-1-P: simulation of a wet deposition; DUNE-1-Q: simulation of a dry deposition) and 2010 (DUNE-2-R1 and DUNE-2-R2: simulation of two successive wet depositions) in the northwestern oligotrophic Mediterranean Sea. No changes in primary production (PP) and chlorophyll a concentrations (Chl a) were observed after a dry deposition event, while a wet deposition event resulted in a rapid (24 h after dust addition), strong (up to 2.4-fold) and long (at least a week in duration) increase in PP and Chl a. We show that, in addition to being a source of dis-solved inorganic phosphorus (DIP), simulated wet deposition events were also a significant source of nitrate (NO − 3) (net in-creases up to +9.8 µM NO − 3 at 0.1 m in depth) to the nutrient-depleted surface waters, due to cloud processes and mixing with anthropogenic species such as HNO 3 . The dry deposi-tion event was shown to be a negligible source of NO − 3 . By transiently increasing DIP and NO − 3 concentrations in N–P starved surface waters, wet deposition of Saharan dust was able to relieve the potential N or NP co-limitation of the phy-toplanktonic activity. Due to the higher input of NO − 3 relative to DIP, and taking into account the stimulation of the bio-logical activity, a wet deposition event resulted in a strong increase in the NO − 3 /DIP ratio, from initially less than 6, to over 150 at the end of the DUNE-2-R1 experiment, suggest-ing a switch from an initial N or NP co-limitation towards a severe P limitation. We also show that the contribution of new production to PP strongly increased after wet dust de-position events, from initially 15 % to 60–70 % 24 h after seeding, indicating a switch from a regenerated-production based system to a new-production based system. DUNE ex-periments show that wet and dry dust deposition events in-duce contrasting responses of the phytoplanktonic commu-nity due to differences in the atmospheric supply of bioavail-able new nutrients. Our results from original mesocosm ex-periments demonstrate that atmospheric dust wet deposition Published by Copernicus Publications on behalf of the European Geosciences Union. 4784 C. Ridame et al.: Phytoplanktonic response to Saharan dust events greatly influences primary productivity and algal biomass in LNLC environments through changes in the nutrient stocks, and alters the NO − 3 /DIP ratio, leading to a switch in the nu-trient limitation of the phytoplanktonic activity

Phytoplanktonic response to contrasted Saharan dust deposition events during mesocosm experiments in LNLC environment

International audienceThe response of the phytoplanktonic community (primary production and algal biomass) to contrasted Saharan dust events (wet and dry deposition) was studied in the framework of the DUNE "a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem" project. We simulated realistic dust deposition events (10 g m-2) into large mesocosms (52 m3). Three distinct experimental dust additions were conducted in June 2008 (DUNE-1-P: simulation of a wet deposition, DUNE-1-Q: simulation of a dry deposition) and 2010 (DUNE-2-R1, -R2: simulation of 2 successive wet depositions) in the northwestern oligotrophic Mediterranean Sea. No changes in primary production (PP) and chlorophyll a concentration (Chl a) were observed after a dry deposition event while a wet deposition event resulted in a rapid (24 h after dust additions), strong (up 2.4 fold) and long (at least a week duration) increase in PP and Chl a. We show that in addition to being a source of dissolved inorganic phosphorus (DIP), simulated wet deposition events were also a significant source of NO3- (net increases up to +9.8 μM NO3- at 0.1 m depth) to the nutrient depleted surface waters due to cloud processes and mixing with anthropogenic species such as HNO3. The dry deposition event was shown to be a negligible source of NO3-. By transiently increasing DIP and NO3- concentrations in P-N starved surface waters, wet deposition of Saharan dust was able to relieve the potential N or NP co-limitation of the phytoplanktonic activity. Due to the higher input of NO3- relative to DIP, a wet deposition event resulted in a strong increase in the NO3-/DIP ratio from initially 3-/DIP ratio leading to a switch in the nutrient limitation of the phytoplanktonic activity

Acetylcholinesterase Inhibitors from a Marine Fungus Talaromyces sp. Strain LF458

Two new oxaphenalenone dimers, talaromycesone A (1) and talaromycesone B (2), and a new isopentenyl xanthenone, talaroxanthenone (3), together with six known diphenyl ether derivatives, e.g., Δ1′,3′,-1′-dehydroxypenicillide (4), 1′,2′-dehydropenicillide (5), vermixocin A (6), vermixocin B (7), 3′-methoxy-1′2′-dehydropenicillide (8), and AS-186c (9), were isolated from the culture broth and mycelia of a marine fungus Talaromyces sp. strain LF458. Compound 2 represents the first example of 1-nor oxaphenalenone dimer carbon skeleton. All isolated compounds were subjected to bioactivity assays. Compounds 1, 2, and 9 exhibited potent antibacterial activities with IC50 3.70, 17.36, and 1.34 μM, respectively, against human pathogenic Staphylococcus strains. Compounds 1, 3, and 9 displayed potent acetylcholinesterase inhibitory activities with IC50 7.49, 1.61, and 2.60 μM, respectively. Interestingly, phosphodiesterase PDE-4B2 was inhibited by compounds 3 (IC50 7.25 μM) and 9 (IC50 2.63 μM)

Engyodontochones, Antibiotic Polyketides from the Marine FungusEngyodontium albumStrain LF069

Six new (2, 4–8) and two known polyketides with a basic structure of an anthraquinone-xanthone were isolated from mycelia and culture broth of the fungus Engyodontium album strain LF069. The structures and relative configurations of these compounds were established by spectroscopic means, and their absolute configurations were defined mainly by comparison of quantum chemical TDDFT calculated and experimental ECD spectra. Compounds 2 and 4–8 were given the trivial names engyodontochone A (2) and B–F (4–8). Compounds 5–8 represent the first example of a 23,28 seco-beticolin carbon skeleton. The relative and absolute configurations of two known substances JBIR-97/98 (1) and JBIR-99 (3) were determined for the first time. All isolated compounds were subjected to bioactivity assays. Compounds 1–4 exhibited inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA) that was 10-fold stronger than chloramphenicol