Linking gene expression to productivity to unravel long-and short-term responses of seagrasses exposed to CO2 in volcanic vents

Ocean acidification is a major threat for marine life but seagrasses are expected to benefit from high CO2. In situ (long-term) and transplanted (short-term) plant incubations of the seagrass Cymodocea nodosa were performed near and away the influence of volcanic CO2 vents at Vulcano Island to test the hypothesis of beneficial effects of CO2 on plant productivity. We relate, for the first time, the expression of photosynthetic, antioxidant and metal detoxification-related genes to net plant productivity (NPP). Results revealed a consistent pattern between gene expression and productivity indicating water origin as the main source of variability. However, the hypothesised beneficial effect of high CO2 around vents was not supported. We observed a consistent long-and short-term pattern of gene downregulation and 2.5-fold NPP decrease in plants incubated in water from the vents and a generalized upregulation and NPP increase in plants from the vent site incubated with water from the Reference site. Contrastingly, NPP of specimens experimentally exposed to a CO2 range significantly correlated with CO2 availability. The down-regulation of metal-related genes in C. nodosa leaves exposed to water from the venting site suggests that other factors than heavy metals, may be at play at Vulcano confounding the CO2 effects.ESF COST Action [ES0906]; Portuguese Foundation for Science and Technology (FCT) [PTDC/MAR-EST/3687/2012]; Italian MIUR Flagship project RITMARE (NRP); FCT [UID/Multi/04326/2013, SFRH/BPD/71129/2010, SFRH/BD/64590/2009]info:eu-repo/semantics/publishedVersio

Epiphytes modulate Posidonia oceanica photosynthetic production, energetic balance, antioxidant mechanisms, and oxidative damage

Epiphytes impose physical barriers to light penetration into seagrass leaves causing shading, which may decrease the production of reactive oxygen species (ROS), but also constitute a physical aggression that may trigger the production of ROS, leading to oxidative damage. Here we investigate the effects of epiphytes on Posidonia oceanica under both interactive perspectives, light attenuation and oxidative stress. Specifically the role of epiphytes in net photosynthesis, chlorophyll a and b, photoprotection (Violaxanthin+Anteraxanthin+Zeaxanthin cycle), soluble sugar and starch contents, enzymatic [ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR)] and global [trolox equivalent antioxidant capacity (TEAC)] and [oxygen radical antioxidant capacity (ORAC)] antioxidant responses, phenolics and oxidative damage (malondialdehyde) are tested. Leaves with epiphytes showed higher chlorophyll b and lower content in VAZ cycle carotenoids. Epiphyte shading was the probable reason for the lower VAZ de-epoxidation-ratio of leaves with epiphytes. In spite of being shaded, leaves with epiphytes showed higher antioxidant levels, indicating that epiphytes trigger the production of ROS. Both ORAC and TEAC and also APX and DHAR activities were higher in leaves with epiphytes, indicating that this response was related with its presence. Malondialdehyde concentrations also suggest oxidative damage caused by epiphytes. We conclude that the epiphyte load causes oxidative stress in P. oceanica and the mechanisms to scavenge ROS were not completely effective to avoid cell damage

Leaf proteome modulation and cytological features of seagrass Cymodocea nodosa in response to long-term high CO2 exposure in volcanic vents

Seagrass Cymodocea nodosa was sampled off the Vulcano island, in the vicinity of a submarine volcanic vent. Leaf samples were collected from plants growing in a naturally acidified site, influenced by the long-term exposure to high CO2 emissions, and compared with others collected in a nearby meadow living at normal pCO(2) conditions. The differential accumulated proteins in leaves growing in the two contrasting pCO(2) environments was investigated. Acidified leaf tissues had less total protein content and the semi-quantitative proteomic comparison revealed a strong general depletion of proteins belonging to the carbon metabolism and protein metabolism. A very large accumulation of proteins related to the cell respiration and to light harvesting process was found in acidified leaves in comparison with those growing in the normal pCO(2) site. The metabolic pathways linked to cytoskeleton turnover also seemed affected by the acidified condition, since a strong reduction in the concentration of cytoskeleton structural proteins was found in comparison with the normal pCO(2) leaves. Results coming from the comparative proteomics were validated by the histological and cytological measurements, suggesting that the long lasting exposure and acclimation of C. nodosa to the vents involved phenotypic adjustments that can offer physiological and structural tools to survive the suboptimal conditions at the vents vicinity

Comparison of different pretreatment processes envisaging the potential use of food waste as microalgae substrate

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 108 cells·mL?1, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of the UIDB/04469/2020 unit, with DOI 10.54499/UIDB/04469/2020, and by LABBELS—Associate Laboratory in Biotechnology, Bioengineering and Micro-electromechanical Systems, LA/P/0029/2020. This work was funded by the European Union throughthe Horizon 2020 research and innovation program under Grant Agreement No 101036388. Pedro Geada acknowledges FCT for the Junior Research contract obtained under the scope of the Scientific Stimulus Employment with the reference 2022.00930.CEECIND (https://doi.org/10.54499/2022.00930.CEECIND/CP1718/CT0023). Ricardo N. Pereira and Joana T. Martins acknowledge FCT for their Assistant Research contract obtained under the scope of Scientific Stimulus Employment with reference CEECIND/02903/2017 (https://doi.org/10.54499/CEECIND/02903/2017/CP1458/CT0006) and 2022.00788.CEECIND/CP1718/CT0024 (https://doi.org/10.54499/2022.00788.CEECIND/CP1718/CT0024), respectively. Luís Machado acknowledges FCT for its fellowship supported by doctoraladvanced training (SFRH/BD/07475/2020).info:eu-repo/semantics/publishedVersio

Responses of zostera marina and cymodocea nodosa to light-limitation stress

The effects of light-limitation stress were investigated in natural stands of the seagrasses Zostera marina and Cymodocea nodosa in Ria Formosa coastal lagoon, southern Portugal. Three levels of light attenuation were imposed for 3 weeks in two adjacent meadows (2–3 m depth), each dominated by one species. The response of photosynthesis to light was determined with oxygen electrodes. Chlorophylls and carotenoids were determined by high-pressure liquid chromatography (HPLC). Soluble protein, carbohydrates, malondialdehyde and phenol contents were also analysed. Both species showed evident signs of photoacclimation. Their maximum photosynthetic rates were significantly reduced with shading. Ratios between specific light harvesting carotenoids and the epoxidation state of xanthophyll cycle carotenoids revealed significantly higher light harvesting efficiency of C. nodosa, a competitive advantage in a low light environment. The contents of both soluble sugars and starch were considerably lower in Z. marina plants, particularly in the rhizomes, decreasing even further with shading. The different carbohydrate energy storage strategies found between the two species clearly favour C. nodosa's resilience to light deprivation, a condition enhanced by its intrinsic arrangement of the pigment pool. On the other hand, Z. marina revealed a lower tolerance to light reduction, mostly due to a less plastic arrangement of the pigment pool and lower carbohydrate storage. Our findings indicate that Z. marina is close to a light-mediated ecophysiological threshold in Ria Formosa

Estimating seagrass community metabolism using benthic chambers: the effect of incubation time

Seagrass meadows are highly productive ecosystems that provide high-value ecosystem services and significantly contribute to carbon sequestration. Net community production (NCP) and community respiration (CR) in seagrass meadows are usually estimated from changes in oxygen concentration during in situ incubations in benthic chambers. Nevertheless, incubation chambers prevent water renovation, thus leading to an increase in pH and O2 and a possible super-saturation inside the chamber, particularly during daytime at high irradiances. We tested the effect of incubation time on seagrass meadows NCP using benthic chambers in a pristine Posidonia oceanica meadow in Corsica, France. Incubations lasting 1.5–2, 3–5, 12, and 24 h were conducted along the day. The results showed that NCP closely follows dial irradiance pattern, with maximum NCP values (23.1 ± 2.8 mmol O2 m−2 h−1) obtained for 1.5-2 h incubations at solar noon. A significant underestimation of NCP budgets was detected with increasing incubation times. When compared to 1.5-2 h incubations, the daylight NCP values obtained for 3-5 h and 12 h incubations underestimated NCP by 24 and 44 %, respectively, while 12 h night incubations underestimated CR by 63 %. When daily budgets were estimated, NCP calculated from 12 and 24 h incubations, the most used incubation times to estimate NCP in P. oceanica, underestimated it by 19 and 76 %, respectively, when compared to the daily budget obtained from 1.5-2 h incubations. Other factors, such as chamber volume and enclosed biomass, in conjunction with incubation time, are also discussed. We showed here that the values of P. oceanica NCP presently reported in the literature may be considerably underestimated. The role of this community as a key carbon sink in the Mediterranean may thus be underrated

Epoxidation state of xanthophyll cycle pigments [EPS = (V + 0.5A)/(V+A+Z)] in <i>Zostera marina</i> and <i>Cymodocea nodosa</i>.

<p>Plants submitted to shading treatments of 24, 40 and 75% of naturally available photosynthetically active radiation (CTRL). Different letters indicate significant differences between treatments, * indicates differences between species (n = 5, <i>p</i><0.05).</p

Total chlorophyll to soluble protein ratio (ChlT/Protein) in leaves of <i>Zostera marina</i> and <i>Cymodocea nodosa</i>.

<p>Plants submitted to shading treatments of 24, 40 and 75% of naturally available photosynthetically active radiation (CTRL). Different letters indicate significant differences between treatments, * indicates differences between species (n = 5, <i>p</i><0.05).</p

Foliar content of photosynthetic pigments in <i>Zostera marina</i> and <i>Cymodocea nodosa</i>.

<p>Plants submitted to shading treatments of 24, 40 and 75% of naturally available photosynthetically active radiation (CTRL). A- Neoxantin, B - Lutein plus Lutein epoxide (LXL), C -Violaxanthin, D –β-Carotene. Different letters indicate significant differences between treatments, * indicates differences between species (n = 5, <i>p</i><0.05).</p

Light response curves of <i>Zostera marina</i> and <i>Cymodocea nodosa</i>.

<p>Plants submitted to shading treatments of 24, 40 and 75% of naturally available photosynthetically active radiation (CTRL). The model equation of Smith and Talling <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081058#pone.0081058-Smith1" target="_blank">[15] </a><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081058#pone.0081058-Talling1" target="_blank">[16]</a> was adjusted to the observed points.</p