Marine heatwaves (MHWs) are increasing in frequency and intensity as part of climate change, yet their impact on seagrass is poorly known. The present work evaluated the physiological and ...morphological responses of Cymodocea nodosa to a MHW. C. nodosa shoots were transplanted into a mesocosm facility. To simulate a MHW, water temperature was raised from 20 to 28 °C, kept 7 days at 28 °C, cooled down back to 20 °C and then maintained at 20 °C during an 8-day recovery period. The potentially stressful effects of the simulated heatwave on the photosynthetic performance, antioxidative-stress level and area vs dry weight ratio of leaves were investigated. The maximum quantum yield of photosystem II (ΦPSII) increased during the heatwave, allowing the plants to maintain their photosynthetic activity at control level. Negative effects on the photosynthetic performance and leaf biomass of C. nodosa were observed during the recovery period. No significant oxidative stress was observed throughout the experiment. Overall, although C. nodosa showed a relative tolerance to MHWs compared to other species, its population in Ria Formosa is likely to be negatively affected by the forecasted climate change scenarios.
Abstract
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 CO
2
emissions, and compared with others collected in a nearby meadow living at normal
p
CO
2
conditions. The differential accumulated proteins in leaves growing in the two contrasting
p
CO
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
p
CO
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
p
CO
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.
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.
The combination of ocean acidification (OA) and global warming is expected to have a significant effect on the diversity and functioning of marine ecosystems, particularly on calcifying algae such as ...rhodoliths (maërl) that form extensive beds worldwide, from polar to tropical regions. In addition, the increasing frequency of extreme events, such as heat waves, threatens coastal ecosystems and may affect their capacity to fix blue carbon. The few studies where the simultaneous effects of both temperature and CO2 were investigated have revealed contradictory results. To assess the effect that high temperature spells can have on the maërl beds under OA, we tested the short‐time effects of temperature and CO2 on the net photosynthesis, respiration, and calcification of the recently described species Phymatolithon lusitanicum, the most common maërl species of southern Portugal. Photosynthesis, calcification, and respiration increased with temperature, and the differences among treatments were enhanced under high CO2. We found that in the short term, the metabolic rates of Phymatolithon lusitanicum will increase with CO2 and temperature as will the coupling between calcification and photosynthesis. However, under high CO2, this coupling will favor photosynthesis over calcification, which, in the long term, can have a negative effect on the blue carbon fixing capacity of the maërl beds from southern Portugal.
In a short term, the effect of increasing CO2 on the metabolic rates of Phymatolithon lusitanicum will be accentuated with increasing temperature.
Circadian regulations are essential for enabling organisms to synchronize physiology with environmental light-dark cycles. Post-transcriptional RNA modifications still represent an understudied level ...of gene expression regulation in plants, although they could play crucial roles in environmental adaptation. N6-methyl-adenosine (m6A) is the most prevalent mRNA modification, established by “writer” and “eraser” proteins. It influences the clockwork in several taxa, but only few studies have been conducted in plants and none in marine plants. Here, we provided a first inventory of m6A-related genes in seagrasses and investigated daily changes in the global RNA methylation and transcript levels of writers and erasers in Cymodocea nodosa and Zostera marina. Both species showed methylation peaks during the dark period under the same photoperiod, despite exhibiting asynchronous changes in the m6A profile and related gene expression during a 24-h cycle. At contrasting latitudes, Z. marina populations displayed overlapping daily patterns of the m6A level and related gene expression. The observed rhythms are characteristic for each species and similar in populations of the same species with different photoperiods, suggesting the existence of an endogenous circadian control. Globally, our results indicate that m6A RNA methylation could widely contribute to circadian regulation in seagrasses, potentially affecting the photo-biological behaviour of these plants.
Pruning is a common practice in citrus for various reasons. These include controlling and shaping the canopy; improving phytosanitary health, productivity, and fruit quality; and facilitating ...operations such as harvesting and phytosanitary treatments. Because pruning is an expensive operation, its need is sometimes questioned. However, it has been proven to be particularly important in Mediterranean citriculture, which is oriented towards producing fruits for a high-quality demanding fresh market. Herein, we summarize and explain the pruning techniques used in Mediterranean citriculture and refer to the main purposes of each pruning type, considering citrus morphology and physiology.
Global climate change, specifically the intensification of marine heatwaves, affect seagrasses. In the Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, ...particularly during low spring tides. However, the photophysiological and antioxidant responses of seagrasses to such extreme events are poorly known. Here, we evaluated the responses of Cymodocea nodosa exposed at 20 °C and 40 °C and 150 and 450 μmol quanta m−2 s−1. After four-days, we analyzed (a) photosynthetic responses to irradiance, maximum photochemical efficiency (Fv/Fm), the effective quantum yield of photosystem II (ɸPSII); (b) soluble sugars and starch; (c) photosynthetic pigments; (d) antioxidant responses (ascorbate peroxidase, APX; oxygen radical absorbance capacity, ORAC, and antioxidant capacity, TEAC); (d) oxidative damage (malondialdehyde, MDA). After four days at 40 °C, C. nodosa showed relevant changes in photosynthetic pigments, independent of light intensity. Increased TEAC and APX indicated an “investment” in the control of reactive oxygen species levels. Dark respiration and starch concentration increased, but soluble sugar concentrations were not affected, suggesting higher CO2 assimilation. Our results show that C. nodosa adjusts its photophysiological processes to successfully handle thermal stress, even under saturating light, and draws a promising perspective for C. nodosa resilience under climate change scenarios.
Rhodolith (maërl) beds are biodiversity hotspots with a worldwide distribution. Maërl is the general term for free-living non-geniculate rhodoliths or coralline red algae. In southern Portugal, maërl ...beds are mainly composed by Phymatolithon lusitanicum, recently identified as a new species and commonly misidentified as Phymatolithon calcareum. Photosynthesis, respiration and growth rates of the algae were measured seasonally, as well as the photosynthetic pigment composition. To characterize the seasonal and interannual patterns of key abiotic conditions in the largest described maërl bed of the Portuguese coast, temperature, irradiance and dissolved oxygen were continuously monitored over a two-year period. At the bed depth (22 meters), temperature ranged between 14 ºC in winter and 24 ºC in summer, irradiance varied from 5 to 75 μmol m-2 s-1 and dissolved oxygen from 5.8 to 7.25 mgO2 L-1. We found a strong linear relationship (r2=0.95) between gross primary production (GPP) and relative electron transport rates (rETR). Both methods led to similar results and an average molar ratio of 0.24. Photosynthesis and respiration increased in summer and decreased in autumn and winter. In the summer of 2013 the growth rates where two fold higher (1.34 µmol CaCO3 g-1day-1) than in the other seasons. In winter and spring, to compensate for light deprivation and low temperature, algae increased their chlorophyll a and carotenoid concentrations while also decreasing their phycobilin concentration, in this case probably due to nutrient limitation. To isolate the role of temperature on the algae’s metabolism, the photosynthetic and respiration rates of individual thalli were measured at 8 different temperatures in the laboratory (from 12 to 26 ºC). Phymatolithon lusitanicum photosynthesis increased 2-fold after a threshold of 18 ºC (from 2.2 at 18 °C to 3.87 µmol O2 m-2 s-1 at 20 °C), whereas respiration increased 4-fold with temperature after a threshold of 22 º C (from -0.38 at 18 °C to -1.81 µmol O2 m-2 s-1 at 24 °C). The significant increases on respiration, photosynthetic rates and maximum growth with temperature reveal that the metabolic rates of P. lusitanicum are highly sensitive to ocean warming.
The circadian clock is an endogenous time-keeping mechanism that enables organisms to adapt to external environmental cycles. It produces rhythms of plant metabolism and physiology, and interacts ...with signaling pathways controlling daily and seasonal environmental responses through gene expression regulation. Downstream metabolic outputs, such as photosynthesis and sugar metabolism, besides being affected by the clock, can also contribute to the circadian timing itself. In marine plants, studies of circadian rhythms are still way behind in respect to terrestrial species, which strongly limits the understanding of how they coordinate their physiology and energetic metabolism with environmental signals at sea. Here, we provided a first description of daily timing of key core clock components and clock output pathways in two seagrass species,
Cymodocea nodosa
and
Zostera marina
(order
Alismatales
), co-occurring at the same geographic location, thus exposed to identical natural variations in photoperiod. Large differences were observed between species in the daily timing of accumulation of transcripts related to key metabolic pathways, such as photosynthesis and sucrose synthesis/transport, highlighting the importance of intrinsic biological, and likely ecological attributes of the species in determining the periodicity of functions. The two species exhibited a differential sensitivity to light-to-dark and dark-to-light transition times and could adopt different growth timing based on a differential strategy of resource allocation and mobilization throughout the day, possibly coordinated by the circadian clock. This behavior could potentially derive from divergent evolutionary adaptations of the species to their bio-geographical range of distributions.
Species of the genus
Asparagopsis
are rich in halogenated bioactive compounds, particularly bromoform. Its use as a feed additive in ruminant livestock drastically decreases the animal’s methane ...production, thereby reducing the industry’s environmental impact. Addressing the high demand for
Asparagopsis
biomass requires the understanding of the culture conditions that promote higher growth rates and bromoform content. Here we evaluated how different light quality combinations (High-Blue:Red, Medium Blue:Red, High-Blue:Green:Red, and White) and four light intensities (30, 60, 90 and 120 μmol photons m
−2
s
−1
) affect the growth and bromoform content of the
Asparagopsis taxiformis
tetrasporophyte in indoor tumbling cultures at two biomass densities. We also assessed the effect of light intensity on the photosynthetic response by measuring oxygen evolution rates. Light spectra containing intermediate wavelengths promoted higher growth, regardless of biomass density. Of the different light qualities tested, white light promoted the highest bromoform content. Increasing light intensity led to a positive response in
A. taxiformis
growth. However, the photosynthetic parameters estimated showed that the two higher light intensity treatments were above the saturation irradiance, for both culture densities. This, along with the observed development of contamination, suggests that long-term cultures of
A. taxiformis
should be maintained at light intensities no higher than 60 μmol photons m
−2
s
−1
. In addition, we found that exposing cultures to higher irradiances does not guarantee a bromoform-richer biomass. These results offer valuable insights for optimizing biomass and bioactive compound production in indoor cultures of the
Asparagopsis
genus.
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