Greenhouse gas (CO2 and CH4) net emission from freshwater wetlands with different primary producer communities

Il presente lavoro di tesi riguarda la regolazione delle emissioni di gas serra da parte di diversi produttori primari all’interno di zone umide d’acqua dolce. In ambienti eutrofici, l’aumento dell’apporto di sostanza organica al sedimento favorisce il mutamento delle comunità vegetali. A seguito dell’aumento della torbidità dell’acqua e della crescita fitoplanctonica, la vegetazione radicata sommersa viene infatti sostituita da specie radicate a foglia galleggiante o da forme pleustofitiche. Queste ultime vengono favorite dalla presenza di acque ricche in nutrienti e a bassa penetrazione della luce. L’ipotesi principale di questo lavoro è che il cambiamento nella composizione vegetale acquatica e la prevalenza di una comunità su un’altra determinino delle modifiche nell’ossigenazione dell’acqua, nella produzione di gas serra nei sedimenti e quindi negli efflussi diretti verso l’atmosfera. In tale contesto, la presenza di vegetazione sommersa riveste un ruolo determinante nel mantenimento dell’ossigenazione dell’acqua e favorisce i processi microbici aerobici (ad esempio, l’ossidazione del metano); al contrario, la barriera fisica creata dalle foglie galleggianti all’interfaccia aria-acqua sostiene condizioni di ipossia in colonna d’acqua e nel sedimento. Come conseguenza principale, vengono favoriti i processi di respirazione e la metanogenesi nel sedimento, così come l’accumulo di metano e anidride carbonica in colonna d’acqua. Al fine di testare queste ipotesi, sono stati condotti due esperimenti in laboratorio in cui è stato studiato il trasporto di ossigeno da parte delle radici di una macrofite radicata sommersa (Vallisneria spiralis), con particolare attenzione agli effetti sull’ossidazione del metano, la fissazione di carbonio e la ritenzione di nutrienti (Capitoli 5 e 6). In secondo luogo, è stato condotto un esperimento di campo al fine di definire il ruolo di una rizofita a foglia galleggiante (Nuphar luteum) nel convogliare metano direttamente dal sedimento all’aria attraverso il parenchima aerifero e nel fissare carbonio sottoforma di biomassa (Capitolo 7). Infine, è stato realizzato un monitoraggio esteso su diverse zone umide colonizzate da diverse comunità vegetali acquatiche, allo scopo di evidenziare l’effetto della colonizzazione da parte di pleustofite sull’ossigenazione della colonna d’acqua e sulle dinamiche temporali dei gas disciolti; sono stati inoltre calcolati dei flussi teorici di gas serra diretti verso l’atmosfera. (Capitolo 8). I risultati di questo studio dimostrano come, seguendo il cambiamento delle comunità vegetali da forme sommerse a forme galleggianti, si assista a un aumento del rilascio di gas serra verso l’atmosfera. Si evidenzia quindi la necessità di approfondire il fenomeno, nell’ottica dell’aumento dei fenomeni di eutrofizzazione a livello globale e della crescente invasione degli ambienti stagnanti da parte delle specie a foglie galleggianti.The present work focuses on the regulation of greenhouse gas emission by different primary producers in shallow freshwater wetlands. In eutrophic environments the increase of organic matter input to the sediment favours the shift of primary producer communities. As a consequence of the increase of water turbidity and phytoplankton growth submerged rooted vegetation is replaced by floating-leaved species. The latter are selected in nutrient-rich and light-limited aquatic bodies. The main hypothesis of the present work is that the shift in plant composition and the prevalence of a community over another one trigger changes in water oxygenation and production of greenhouse gas (CO2 and CH4) in the sediment and thus the efflux towards the atmosphere. In this context, the presence of submerged aquatic vegetation plays a major role in maintaining water oxygenation and favour aerobic microbial processes (e.g. methane oxidation), whereas the physical barrier created by floating-leaved and free-floating macrophytes at the water-air interface supports anoxic conditions in the water column and in the sediment. As a main consequence, respiration processes and methanogenesis in the sediment are favoured, as well as the accumulation of methane and carbon dioxide in the water column. To test these hypotheses, two laboratory experiments were performed to investigate the oxygen transport to the rhizosphere by a submerged rooted macrophyte (Vallisneria spiralis) and its subsequent effects on methane oxidation, carbon fixation and nutrients retention (Chapters 5 and 6). Secondly, an in situ experiment was carried out to define the role of a floating-leaved macrophyte (Nuphar luteum) in conveying methane from the sediment to the air through the aerenchyma and fixing carbon dioxide in biomass (Chapter 7). Finally, an in situ monitoring was performed over a range of shallow wetlands colonized by different primary producers, with the aim of investigating the effect of the colonization of free-floating macrophytes on water oxygenation and seasonal gas dynamics in water; theoretical greenhouse gas fluxes were also calculated (Chapter 8). Results from the present study show that, following the shift of primary producers from submerged to floating forms, an increasing amount of greenhouse gases is released to the atmosphere. This outcome should be of global concern when considering the raising of aquatic environments that suffer from eutrophication and that are undergoing to regime shift; those environments are likely to be colonized by free-floating plants and significantly affect the global trace gas budget

CO2 and CH4 fluxes across a Nuphar lutea (L.) Sm. stand

Floating-leaved rhizophytes can significantly alter net carbon dioxide (CO 2) and methane (CH 4) exchanges with the atmosphere in freshwater shallow environments. In particular, CH 4 efflux can be enhanced by the aerenchyma-mediated mass flow, while CO 2 release from supersaturated waters can be reversed by the plant uptake. Additionally, the floating leaves bed can hamper light penetration and oxygen (O 2) diffusion from the atmosphere, thus altering the dissolved gas dynamics in the water column. In this study, net fluxes of CO 2 and CH 4 were measured seasonally across vegetated [Nuphar lutea (L.) Sm.] and free water surfaces in the Busatello wetland (Northern Italy). Concomitantly, dissolved gas concentrations were monitored in the water column and N. lutea leaf production was estimated by means of biomass harvesting. During the vegetative period (May-August), the yellow waterlily stand resulted a net sink for atmospheric carbon (from 97.5 to 110.6 g C-CO 2 m -2), while the free water surface was a net carbon source (166.3 g C-CO 2 m -2). Both vegetated and plant-free areas acted as CH 4 sources, with an overall carbon release comprised between 71.6 and 113.3 g C-CH 4 m -2. On the whole, water column chemistry was not affected by the presence of the floating leaves; moreover, no significant differences in CH4 efflux were evidenced between the vegetated and plant-free areas. In general, this study indicates that the colonization of shallow aquatic ecosystems by N. lutea might not have the same drastic effect reported for free-floating macrophytes

Invasive Aquatic Plants as Ecosystem Engineers in an Oligo-Mesotrophic Shallow Lake

Exotic hydrophytes are often considered as aquatic weeds, especially when forming dense mats on an originally poorly colonized environment. While management efforts and research are focused on the control and on the impacts of aquatic weeds on biodiversity, their influence on shallow lakes’ biogeochemical cycles is still unwell explored. The aim of the present study is to understand whether invasive aquatic plants may affect the biogeochemistry of shallow lakes and act as ecosystem engineers. We performed a multi-year investigation (2013–2015) of dissolved biogeochemical parameters in an oligo-mesotrophic shallow lake of south-west of France (Lacanau Lake), where wind-sheltered bays are colonized by dense mats of exotic Egeria densa Planch. and Lagarosiphon major (Ridl.) Moss. We collected seasonal samples at densely vegetated and plant-free areas, in order to extrapolate and quantify the role of the presence of invasive plants on the biogeochemistry, at the macrophyte stand scale and at the lake scale. Results revealed that elevated plant biomass triggers oxygen (O2), dissolved inorganic carbon (DIC) and nitrogen (DIN) stratification, with hypoxia events frequently occurring at the bottom of the water column. Within plants bed, elevated respiration rates generated important amounts of carbon dioxide (CO2), methane (CH4) and ammonium (NH4+). The balance between benthic nutrients regeneration and fixation into biomass results strictly connected to the seasonal lifecycle of the plants. Indeed, during summer, DIC and DIN regenerated from the sediment are quickly fixed into plant biomass and sustain elevated growth rates. On the opposite, in spring and autumn, bacterial and plant respiration overcome nutrients fixation, resulting in an excess of nutrients in the water and in the increase of carbon emission toward the atmosphere. Our study suggests that aquatic weeds may perform as ecosystem engineers, by negatively affecting local oxygenation and by stimulating nutrients regeneration

Psychiatric Disorders and Oxidative Injury: Antioxidant Effects of Zolpidem Therapy disclosed In Silico

Zolpidem (N,N-Dimethyl-2-[6-methyl-2-(4-methylphenyl)imidazo[1,2-a]pyridin-3-yl]acetamide) is a well-known drug for the treatment of sleeping disorders. Recent literature reports on positive effects of zolpidem therapy on improving renal damage after cisplatin and on reducing akinesia without sleep induction. This has been ascribed to the antioxidant and neuroprotective capacity of this molecule, and tentatively explained according to a generic structural similarity between zolpidem and melatonin. In this work, we investigate in silico the antioxidant potential of zolpidem as scavenger of five ROSs, acting via hydrogen atom transfer (HAT) mechanism; computational methodologies based on density functional theory are employed. For completeness, the analysis is extended to six metabolites. Thermodynamic and kinetic results disclose that indeed zolpidem is an efficient radical scavenger, similarly to melatonin and Trolox, supporting the biomedical evidence that the antioxidant potential of zolpidem therapy may have a beneficial effect against oxidative injury, which is emerging as an important etiopathogenesis in numerous severe diseases, including psychiatric disorders

Rôle fonctionnel, dynamiques écologiques et nécessité de gestion des communautés d’isoétides dans les lacs et étangs du littoral aquitain

Les lacs et étangs du littoral aquitain ont l’originalité d’abriter des plantes aquatiques protégées, rares et menacées, habituellement observées dans les régions boréo-atlantiques du nord de l’Europe. Ces plantes de petite taille, qui appartiennent à la communauté végétale des isoétides, composent des pelouses littorales rases souvent invisibles aux yeux des usagers des lacs. Ces plantes font l’objet de recherches scientifiques afin de déterminer leur rôle fonctionnel et leurs dynamiques écologiques dans les lacs peu profonds. L’acquisition de connaissances sur ces espèces a pour objectif d’aider à la gestion de l’ensemble des peuplements végétaux aquatiques dans les lacs et étangs aquitains. Les isoétides sont capables de transférer l’oxygène produit dans le sédiment lacustre et de contrôler les émissions de méthane. Les processus écologiques en cours depuis les quarante dernières années indiquent un déclin régulier des isoétides dans les lacs landais. L’action des vagues et l’exposition aux vents, l’occupation du sol sur les rives et les altérations physiques ponctuelles de l’hydromorphologie sont les paramètres physiques essentiels des biotopes aquatiques qui déterminent la répartition spatiale des isoétides dans les plans d’eau. Il est désormais urgent d’établir et d’appliquer une stratégie de conservation, voire de restauration, des isoétides, visant à préserver les niveaux trophiques actuels relativement faibles, et à les protéger des destructions mécaniques directes dans les zones littorales. Les résultats présentés dans cet article sont extraits et adaptés de travaux réalisés par INRAE (ex-Irstea) dans le cadre d’un post-doctorat et d’un doctorat financés par l’Agence de l’Eau Adour-Garonne.Natural lakes and ponds located along the western French Atlantic coast shelter rare and endangered aquatic plants usually found in the North-Atlantic Boreal regions in Europe. These small plants, belonging to the isoetid plant community, constitute shoreline lawns hardly visible to lake users. Here we aim to determine the functional role and ecological dynamics of isoetids in these shallow lakes. Isoetids transfer radial oxygen in sediment and control methane emissions. Aquatic plant community dynamics indicate a decline in the occurrence and the abundance of isoetids over the last forty years. We highlight the role of wave action and wind exposure, land cover and anthropogenic physical disturbances of the shoreline in determining the spatial distribution of isoetids. Now, it is urgent to establish and implement a conservation strategy dedicated to isoetids, in order to preserve the current oligotrophic water quality of lakes and protect these species from direct mechanical destruction in lake littoral zones

Front. Plant Sci.

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Minor Protease Inhibitor Mutations at Baseline Do Not Increase the Risk for a Virological Failure in HIV-1 Subtype B Infected Patients

BACKGROUND: Minor protease inhibitor (PI) mutations often exist as polymorphisms in HIV-1 sequences from treatment-naïve patients. Previous studies showed that their presence impairs the antiretroviral treatment (ART) response. Evaluating these findings in a larger cohort is essential. METHODS: To study the impact of minor PI mutations on time to viral suppression and time to virological failure, we included patients from the Swiss HIV Cohort Study infected with HIV-1 subtype B who started first-line ART with a PI and two nucleoside reverse transcriptase inhibitors. Cox regression models were performed to compare the outcomes among patients with 0 and ≥ 1 minor PI mutation. Models were adjusted for baseline HIV-1 RNA, CD4 cell count, sex, transmission category, age, ethnicity, year of ART start, the presence of nucleoside reverse transcriptase inhibitor mutations, and stratified for the administered PIs. RESULTS: We included 1199 patients of whom 944 (78.7%) received a boosted PI. Minor PI mutations associated with the administered PI were common: 41.7%, 16.1%, 4.7% and 1.9% had 1, 2, 3 or ≥ 4 mutations, respectively. The time to viral suppression was similar between patients with 0 (reference) and ≥ 1 minor PI mutation (multivariable hazard ratio (HR): 1.1 [95% confidence interval (CI): 1.0-1.3], P = .196). The time to virological failure was also similar (multivariable HR:.9 [95% CI:.5-1.6], P = .765). In addition, the impact of each single minor PI mutation was analyzed separately: none was significantly associated with the treatment outcome. CONCLUSIONS: The presence of minor PI mutations at baseline has no effect on the therapy outcome in HIV infected individuals

Les plans d’eau, des alliés face au changement climatique

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1970-2020 : 50 ans d'hydrophytes invasives dans les grands lacs aquitains

Certaines plantes aquatiques exotiques présentent des traits biologiques qui leur confèrent des avantages dans la colonisation des milieux aquatiques (taux de croissance, stratégie de reproduction, utilisation des ressources…). Parmi elles, certaines hydrophytes sont dites « invasives » dès que leur abondance génère des problèmes d’ordre écologique et entrave le déroulement de certains usages humains. En Nouvelle Aquitaine, dans les grands lacs de la façade atlantique, deux espèces ont désormais des impacts avérés (Lagarosiphon major et Egeria densa) et une est en cours d’expansion (Sagittaria graminea). Alors que les efforts de gestion se concentrent sur l'éradication des herbiers denses, l’influence des herbiers aquatiques sur le fonctionnement chimique et biologique des lacs peu profonds est encore mal explorée. Nous présentons ici l’éventail d’études menées par les scientifiques depuis les années 1970 dans les grands lacs du littoral aquitain, qui montre l’évolution des protocoles et la variété des approches appliquées à la problématique. Ces études ont pour objectif principal d’aider à orienter les stratégies de gestion pour la régulation des espèces exotiques envahissantes en milieu lacustre

L'exposition au vent inhibe l'hypoxie dans les herbiers denses d'hydrophytes invasives

International audienceLa présence d’herbiers denses d’hydrophytes invasives dans les lacs peu profonds génère localement des phénomènes de stratification thermique et trophique, ainsi que l’accumulation de matière organique labile. L'apparition de conditions hypoxiques dans l’eau a des effets en cascade sur la respiration bactérienne, comme la méthanogenèse et l'ammonification et, en général, affecte négativement les organismes benthiques et pélagiques. Les baisses d’oxygène peuvent cependant être atténuées par des épisodes de vent fort, qui favorisent le brassage et la réoxygénation de la colonne l'eau. La présente étude vise à relier explicitement l'action du vent et l'oxygénation de l'eau dans les herbiers denses d'hydrophytes des lacs peu profonds. Dans ce but, des campagnes saisonnières de cycles nycthéméraux ont été réalisées (2013-2017) et des sondes autonomes ont été déployées (2016-2018) pour la mesure de l’oxygène dissous dans deux lacs peu profonds, caractérisés par la présence d’herbiers denses d’hydrophytes invasives, ainsi que par différents niveaux trophiques et différentes conditions d’exposition au vent. Les résultats montrent que les patrons journaliers et saisonniers d'oxygène dissous sont fortement affectés par le degré d'exposition au vent. La survenue d'épisodes de vent fréquents favorise le brassage des eaux près du fond, et facilite l'apport mécanique d'oxygène provenant de l'atmosphère ou de la zone pélagique, même pendant la période de croissance maximale des plantes aquatiques. Afin d’utiliser cette étude comme aide à la gestion, nous avons créé un modèle reliant l'exposition au vent (indice de Keddy) et l'oxygénation de l'eau, qui nous a permis de produire une carte de risque identifiant géographiquement les sites abrités du vent comme les plus soumis à des périodes critiques d’hypoxie