Posts Tagged 'phanerogams'

Genome-wide transcriptional reprogramming in the seagrass Cymodocea nodosa under experimental ocean acidification

Here we report the first use of massive scale RNA-Sequencing to explore seagrass response to CO2-driven ocean acidification (OA). Large-scale gene expression changes in the seagrass Cymodocea nodosa occurred at CO2 levels projected by the end of the century. C. nodosatranscriptome was obtained using Illumina RNA-Seq technology and de novo assembly, and differential gene expression was explored in plants exposed to short-term high CO2 / low pH conditions. At high pCO2, there was a significant increased expression of transcripts associated to photosynthesis, including light reaction functions and CO2 fixation, and also to respiratory pathways, specifically for enzymes involved in glycolysis, in the tricarboxylic acid cycle and in the energy metabolism of the mitochondrial electron transport. The up-regulation of respiratory metabolism is probably supported by the increased availability of photosynthates and increased energy demand for biosynthesis and stress-related processes under elevated CO2 and low pH. The up-regulation of several chaperones resembling heat stress-induced changes in gene expression, highlighted the positive role these proteins play in tolerance to intracellular acid stress in seagrasses. OA further modifies C. nodosa secondary metabolism inducing the transcription of enzymes related to carbon-based-secondary compounds biosynthesis, in particular the synthesis of polyphenols and isoprenoid compounds that have a variety of biological functions including plant defense. By demonstrating which physiological processes are most sensitive to OA, this research provide a major advance in the understanding of seagrass metabolism in the context of altered seawater chemistry from global climate change.

Continue reading ‘Genome-wide transcriptional reprogramming in the seagrass Cymodocea nodosa under experimental ocean acidification’

Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment

Seagrasses are often regarded as climate change ‘winners’ because they exhibit higher rates of photosynthesis, carbon fixation and growth when exposed to increasing levels of ocean acidification. However, questions remain whether such growth enhancement compromises the biomechanical properties of the plants, altering their vulnerability to structural damage and leaf loss. Here, we investigated the short-term (6 wk) effects of decreasing pH by CO2 enrichment on the growth, morphology and leaf-breaking force of the temperate seagrass Cymodocea nodosa. We found that the plant biomass balance under levels of acidification representative of short-term climate change projections (pH 8.04) was positive and led to an increase in leaf abundance in the shoots. However, we also found that plant biomass balance was negative under levels of acidification experienced presently (pH 8.29) and those projected over the long-term (pH 7.82). Leaf morphology (mean leaf length, thickness and width) was invariant across our imposed acidification gradient, although leaves were slightly stronger under [CO2] representative of short-term climate change. Taken together, these findings indicate that a subtle increase in growth and mechanical resistance of C. nodosa is likely to occur following short- to medium-term changes in ocean chemistry, but that these positive effects are unlikely to be maintained over the longer term. Our study emphasises the need to account for the interdependencies between environmental conditions and variations in multiple aspects of the structure and functioning of seagrass communities when considering the likely consequences of climate change.

Continue reading ‘Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment’

Altered epiphyte community and sea urchin diet in Posidonia oceanica meadows in the vicinity of submarine volcanic CO2 vents

Ocean acidification (OA) predicted for 2100 is expected to shift seagrass epiphyte communities towards the dominance of more tolerant non-calcifying taxa. However, little is known about the indirect effects of such changes on food provision to key seagrass consumers. We found that epiphyte communities of the seagrass Posidonia oceanica in two naturally acidified sites (i.e. north and south sides of a volcanic CO2 vent) and in a control site away from the vent at the Ischia Island (NW Mediterranean Sea) significantly differed in composition and abundance. Such differences involved a higher abundance of non-calcareous crustose brown algae and a decline of calcifying polychaetes in both acidified sites. A lower epiphytic abundance of crustose coralline algae occurred only in the south side of the vents, thus suggesting that OA may alter epiphyte assemblages in different ways due to interaction with local factors such as differential fish herbivory or hydrodynamics. The OA effects on food items (seagrass, epiphytes, and algae) indirectly propagated into food provision to the sea urchin Paracentrotus lividus, as reflected by a reduced P. oceanica exploitation (i.e. less seagrass and calcareous epiphytes in the diet) in favour of non-calcareous green algae in both vent sites. In contrast, we detected no difference close and outside the vents neither in the composition of sea urchin diet nor in the total abundance of calcareous versus non-calcareous taxa. More research, under realistic scenarios of predicted pH reduction (i.e. ≤ 0.32 units of pH by 2100), is still necessary to better understand cascading effects of this altered urchin exploitation of food resources under acidified conditions on ecosystem diversity and function.

Continue reading ‘Altered epiphyte community and sea urchin diet in Posidonia oceanica meadows in the vicinity of submarine volcanic CO2 vents’

Effects of in situ CO2 enrichment on Posidonia oceanica epiphytic community composition and mineralogy

Alterations in seagrass epiphytic communities are expected under future ocean acidification conditions, yet this hypothesis has been little tested in situ. A Free Ocean Carbon Dioxide Enrichment system was used to lower pH by a ~0.3 unit offset within a partially enclosed portion (1.7 m3) of a Posidonia oceanica meadow (11 m depth) between June 21 and November 3, 2014. Leaf epiphytic community composition (% cover) and bulk epiphytic mineralogy were compared every 4 weeks within three treatments, located in the same meadow: a pH-manipulated (experimental enclosure) and a control enclosure, as well as a nearby ambient area. Percent coverage of invertebrate calcifiers and crustose coralline algae (CCA) did not appear to be affected by the lowered pH. Furthermore, fleshy algae did not proliferate at lowered pH. Only Foraminifera, which covered less than 3% of leaf surfaces, declined in manner consistent with ocean acidification predictions. Bulk epiphytic magnesium carbonate composition was similar between treatments and percentage of magnesium appeared to increase from summer to autumn. CCA did not exhibit any visible skeleton dissolution or mineral alteration at lowered pH and carbonate saturation state. Negative impacts from ocean acidification on P. oceanica epiphytic communities were smaller than expected. Epiphytic calcifiers were possibly protected from the pH treatment due to host plant photosynthesis inside the enclosure where water flow is slowed. The more positive outcome than expected suggests that calcareous members of epiphytic communities may find refuge in some conditions and be resilient to environmentally relevant changes in carbonate chemistry.

Continue reading ‘Effects of in situ CO2 enrichment on Posidonia oceanica epiphytic community composition and mineralogy’

Halocarbon emissions by selected tropical seaweeds: species-specific and compound-specific responses under changing pH

Five tropical seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C. Silva, Padina australis Hauck, Sargassum binderi Sonder ex J. Agardh (syn. S. aquifolium (Turner) C. Agardh), Sargassum siliquosum J. Agardh and Turbinaria conoides (J. Agardh) Kützing, were incubated in seawater of pH 8.0, 7.8 (ambient), 7.6, 7.4 and 7.2, to study the effects of changing seawater pH on halocarbon emissions. Eight halocarbon species known to be emitted by seaweeds were investigated: bromoform (CHBr3), dibro­momethane (CH2Br2), iodomethane (CH3I), diiodomethane (CH2I2), bromoiodomethane (CH2BrI), bromochlorometh­ane (CH2BrCl), bromodichloromethane (CHBrCl2), and dibro­mochloromethane (CHBr2Cl). These very short-lived halocarbon gases are believed to contribute to stratospheric halogen concentrations if released in the tropics. It was observed that the seaweeds emit all eight halocarbons assayed, with the exception of K. alvarezii and S. binderi for CH2I2 and CH3I respectively, which were not measurable at the achievable limit of detection. The effect of pH on halocarbon emission by the seaweeds was shown to be species-specific and compound specific. The highest percentage changes in emissions for the halocarbons of interest were observed at the lower pH levels of 7.2 and 7.4 especially in Padina australis and Sargassum spp., showing that lower seawater pH causes elevated emissions of some halocarbon compounds. In general the seaweed least affected by pH change in terms of types of halocarbon emission, was P. australis. The commercially farmed seaweed K. alvarezii was very sensitive to pH change as shown by the high increases in most of the compounds in all pH levels relative to ambient. In terms of percentage decrease in maximum quantum yield of photosynthesis (Fv∕Fm) prior to and after incubation, there were no significant correlations with the various pH levels tested for all seaweeds. The correlation between percentage decrease in the maximum quantum yield of photosynthesis (Fv∕Fm) and halocarbon emission rates, was significant only for CH2BrCl emission by P. australis (r = 0.47; p ≤ 0.04), implying that photosynthesis may not be closely linked to halocarbon emissions by the seaweeds studied. Bromine was the largest contributor to the total mass of halogen emitted for all the seaweeds at all pH. The highest total amount of bromine emitted by K. alvarezii (an average of 98% of total mass of halogens) and the increase in the total amount of chlorine with decreasing seawater pH fuels concern for the expanding seaweed farming activities in the ASEAN region.

Continue reading ‘Halocarbon emissions by selected tropical seaweeds: species-specific and compound-specific responses under changing pH’

Experimental impacts of climate warming and ocean carbonation on eelgrass Zostera marina

CO2 is a critical and potentially limiting substrate for photosynthesis of both terrestrial and aquatic ecosystems. In addition to being a climate-warming greenhouse gas, increasing concentrations of CO2 will dissolve in the oceans, eliciting both negative and positive responses among organisms in a process commonly known as ocean acidification. The dissolution of CO2 into ocean surface waters, however, also increases its availability for photosynthesis, to which the highly successful, and ecologically important, seagrasses respond positively. Thus, the process might be more accurately characterized as ocean carbonation. This experiment demonstrated that CO2 stimulation of primary production enhances the summertime survival, growth, and proliferation of perennial eelgrass Zostera marina from the Chesapeake region, which is regularly impacted by summer heat stress. The experiment also quantified the logarithmic response to CO2 in terms of shoot proliferation, size, growth and sugar accumulation that was fundamentally consistent with model predictions based on metabolic carbon balance derived from short-term laboratory experiments performed with other eelgrass populations from cool ocean climates and other seagrass species from tropical and temperate environments. Rather than acting in a neutral fashion or as an independent stressor, increased CO2 availability can serve as a quantitative antagonist to counter the negative impact of climate warming on seagrass growth and survival. These results reinforce the emerging paradigm that seagrasses are likely to benefit significantly from a high-CO2 world.

Continue reading ‘Experimental impacts of climate warming and ocean carbonation on eelgrass Zostera marina’

The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment

Seagrasses are distributed across the globe and their communities may play key roles in the coastal ecosystems. Seagrass meadows are expected to benefit from the increased carbon availability which might be used in photosynthesis in a future high CO2 world. The main aim of this study was to examine the effect of elevated pCO2 on the net photosynthesis of seagrass Zostera marina in a brackish water environment. The short-term mesocosm experiments were conducted in Kõiguste Bay (northern part of Gulf of Riga, the Baltic Sea) in June–July 2013 and 2014. As the levels of pCO2 naturally range from ca. 150 μatm to well above 1000 μatm under summer conditions in Kõiguste Bay we chose to operate in mesocosms with the pCO2 levels of ca. 2000, ca. 1000, and ca. 200 μatm. Additionally, in 2014 the photosynthesis of Z. marina was measured outside of the mesocosm in the natural conditions. In the shallow coastal Baltic Sea seagrass Z. marina lives in a highly variable environment due to seasonality and rapid changes in meteorological conditions. This was demonstrated by the remarkable differences in water temperatures between experimental years of ca. 8°C. Thus, the current study also investigated the effect of elevated pCO2 in combination with short-term natural fluctuations of environmental factors, i.e., temperature and PAR on the photosynthesis of Z. marina. Our results show that elevated pCO2 alone did not enhance the photosynthesis of the seagrass. The photosynthetic response of Z. marina to CO2 enrichment was affected by changes in water temperature and light availability.

Continue reading ‘The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment’


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Ocean acidification in the IPCC AR5 WG II

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