Excess Irradiance Research Articles

The use of amino acids as bioactive substance: a strategy to increase yield in summer arugula (Eruca sativa L. Mill) crops

Foliar application of amino acids can assist crops to maintain homeostasis under diurnal temperature variations and excessive solar irradiance. The objectives of this study were to investigate the effects of the organic fraction and mineral nutrients of an amino acid solution on arugula plants and the effects of weekly applications of this solution on their growth and biomass yield. Two experiments were conducted in a completely randomized design, in a greenhouse (Experiment 1) and on open-field benches (Experiment 2), in Iracemápolis, SP, Brazil. Experiment 1 consisted of foliar applications of water (control), a solution containing 59 and 40.9 g ha-1 of nitrogen and sulfur, respectively (N+S), and a solution containing 85 g ha-1 of amino acids, with seven replications. Experiment 2 consisted of four different number (0, 1, 2, and 3) of weekly foliar applications of 85 g ha-1 of amino acids, with six replications. Chlorophyll a fluorescence, chlorophyll and carotenoid contents, and fresh and dry biomass weights were evaluated in both experiments. In Experiment 1, shoot fresh weight of plants treated with amino acids increased by 21% and 6% compared to those in the control and N+S treatment, respectively. Amino acid application increased chlorophyll and carotenoid contents, improving photosynthetic performance by increasing effective quantum efficiency of photosystem II and photochemical quenching. In Experiment 2, weekly application of 85 g ha-1 of amino acids increased shoot fresh weight by approximately 10% per application. Therefore, foliar application of amino acids can increase fresh biomass of arugula plants grown under both mild and warmer climate conditions.

Climate Change Stressors, Phosphate Limitation, and High Irradiation Interact to Increase Alexandrium minutum Toxicity and Modulate Encystment Rates.

The changes in the cell physiology (growth rate, cell size, and cell DNA content), photosynthetic efficiency, toxicity, and sexuality under variable light and nutrient (phosphates) conditions were evaluated in cultures of the dinoflagellate Alexandrium minutum obtained from a red tide in the Ría de Vigo (NW Spain). The cells were grown at low (40 and 150 µE m-2 s-1), moderate (400 µE m-2 s-1), and high (800 µE m-2 s-1) light intensities in a medium with phosphate (P+) and without (P-). Cultures were acclimated to the irradiance conditions for one week, and the experiment was run for ~1 month. The cell size and DNA content were monitored via flow cytometry. Two different clonal strains were employed as a monoculture (in a P- or P+ medium) or, to foster sexuality and resting cyst formation, as a mixed culture (only in a P- medium). A. minutum growth was favored by increasing light intensities until 400 µE m-2 s-1. The DNA content analyses indicated the accumulation of S-phase cells at the highest light intensities (400 and 800 µE m-2 s-1) and therefore the negative effects on cell cycle progression. Only when the cells were grown in a P- medium did higher light intensities trigger dose-dependent, significantly higher toxicities in all the A. minutum cultures. This result suggests that the toxicity level is responsive to the combined effects of (high) light and (low) P stress. The cell size was not significantly affected by the light intensity or P conditions. The optimal light intensity for resting cyst formation was 150 µE m-2 s-1, with higher irradiances reducing the total encystment yield. Encystment was not observed at the lowest light intensity tested, indicative of the key role of low-level irradiance in gamete and/or zygote formation, in contrast to the stressor effect of excessive irradiance on planozygote formation and/or encystment.

Effects of surface geometry on light exposure, photoacclimation and photosynthetic energy acquisition in zooxanthellate corals.

Symbiotic corals display a great array of morphologies, each of which has unique effects on light interception and the photosynthetic performance of in hospite zooxanthellae. Changes in light availability elicit photoacclimation responses to optimize the energy balances in primary producers, extensively documented for corals exposed to contrasting light regimes along depth gradients. Yet, response variation driven by coral colony geometry and its energetic implications on colonies with contrasting morphologies remain largely unknown. In this study, we assessed the effect of the inclination angle of coral surface on light availability, short- and long-term photoacclimation responses, and potential photosynthetic usable energy. Increasing surface inclination angle resulted in an order of magnitude reduction of light availability, following a linear relationship explained by the cosine law and relative changes in the direct and diffuse components of irradiance. The light gradient induced by surface geometry triggered photoacclimation responses comparable to those observed along depth gradients: changes in the quantum yield of photosystem II, photosynthetic parameters, and optical properties and pigmentation of the coral tissue. Differences in light availability and photoacclimation driven by surface inclination led to contrasting energetic performance. Horizontally and vertically oriented coral surfaces experienced the largest reductions in photosynthetic usable energy as a result of excessive irradiance and light-limiting conditions, respectively. This pattern is predicted to change with depth or local water optical properties. Our study concludes that colony geometry plays an essential role in shaping the energy balance and determining the light niche of zooxanthellate corals.

Intermittent shading can moderate coral bleaching on shallow reefs

The health of coral reefs is declining from the effects of human activity and climate change. Mass coral bleaching is often triggered by elevated water temperature and excessive solar irradiance. Shading can reduce coral bleaching risk. Shading-based management interventions, such as whole-of-reef marine fogging, have been proposed as a conservation tool for periods when coral undergoes excessive thermal stress. This study examined the effect of intermittent shade (30% for 0, 4, or 24 h) on two coral species, Duncanopsammia axifuga and Turbinaria reniformis, held at either 26.4°C or 32.4°C for 18 days. Coral fragments were assessed for bleaching (relative mean intensity of grey, chlorophyll a, and symbiont density), photochemistry (PAM fluorometry), and antioxidant biomarkers (SOD and CAT). Shading responses were species-specific, with T. reniformis more responsive to shading than D. axifuga. Thirty per cent shading delayed bleaching up to three-degree heat weeks (DHW), and 24 h shade was more protective than 4 h shade. Shading suppressed catalase activity in T. reniformis. Overall, our results suggest that intermittently shading corals for 4 h can moderate light stress and slow bleaching in some corals and could improve the efficiency of active solar radiation management in marine ecosystems.

Biochemical and physiological mechanisms allowing olive trees to survive and produce under water stress conditions

The beneficial properties of olive (Olea europaea L.) edible fruits and their oil play an important part in our diet. Severe summer conditions, including low rainfall, excessive heat load and high daily irradiance, characterize arid and semiarid regions where olive is produced. Although it is highly aggravated by other stresses, water stress is usually the most critical during summer-time. Under severe water stress conditions, a cultivar of any olive tree needs specific biochemical and physiological mechanisms in order to survive and be productive. It is well-known that these water stress resistance mechanisms generally act simultaneously. Nevertheless, water stress adaptability not only integrates the water stress resistance concept (i.e., escape, avoidance and/or tolerance to water stress) but also the recovery capacity. All of them play a major role in plants’ growth and survival, especially when plants are continuously exposed to repeated events of water stress and adequate water levels during their lifetime. Water stress, heat and high irradiance, especially in association with each other, also damage plant functions. As a result, different resistance mechanisms are adopted by plants. This review summarizes each of these mechanisms.

How do barley plants with impaired photosynthetic light acclimation survive under high-light stress?

Main ConclusionWHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione.Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley (Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α-tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.

Particle films improve photosynthesis of citrus trees under excess irradiance by reducing leaf temperature

High irradiance and increased air temperature during extreme weather conditions affect tree crops and impact the yield and quality of fruits. Moreover, flowering and fruit set of Citrus are likely impaired by UV radiation and/or reduced carbon assimilation, which increase reactive oxygen species production and damage the leaf photosynthetic apparatus. Particle coating films sprayed on leaves have been offered as a way to minimize crop losses due to the climate change scenario, even though the extent of leaf protection is not characterized. We evaluated the use of two protective films on the oxidative stress and leaf photosynthesis of sweet orange trees exposed to varying daylight levels. Trees were maintained under full sun light, sprayed or not (control) with kaolin or calcium carbonate, and under reduced irradiance using either aluminum shade cloth 50% or anti-UV transparent plastic. Kaolin or calcium carbonate reflected 20%-30% of the incident light on the leaf surface compared to leaves not sprayed and under full sunlight. Leaves with coating exhibited improved CO2 assimilation and photosystem II efficiency, and lower leaf temperatures over time. In addition, the coating protected leaves against excess irradiance due to dissipation of excess energy into the photosynthetic apparatus (NPQt). Nonenzymatic mechanisms for UV protection, such as carotenoids, were higher in full sun control plants than in leaf-coated plants. Comparable responses were observed on trees maintained covered either by the cloth or the plastic film. Finally, we conclude that the use of suspension particles mitigates the harmful effects of excess UV irradiance and temperature in sweet orange trees.

Large-scale effects of turbidity on coral bleaching in the Hawaiian islands

Turbidity from land-based runoff has been identified as a possible driver of coral bleaching refugia, as particulate matter in turbid habitats may block excessive irradiance and alter the food supply to corals during ocean heatwaves. However, negative effects of turbidity have also been documented worldwide, and high-resolution data across reef regions are required to identify habitats where turbidity is harmful or helpful during heatwaves. We monitored turbidity across five Main Hawaiian Islands during a 2019 ocean heatwave using Planet Dove satellites (3.7 m spatial resolution, extracted at 100 m resolution) to examine relationships between turbidity and coral bleaching occurrence and severity. We also attributed turbidity to urban and non-urban land uses to determine how turbidity associated with different human activities affects coral bleaching. We found that, while turbidity had a negative relationship with coral bleaching severity, this effect weakened at higher temperatures, especially in rural areas. However, turbidity maintained a slightly negative effect on bleaching severity in urban settings. In addition, while thermal stress was the predominant driver of bleaching occurrence, interactions between temperature and local variables like turbidity and wave energy were the most significant drivers of bleaching severity. This study represents one of the first high-resolution analyses of turbid refugia at large spatial scales. We show how new data sources from remote sensing can provide scalable yet context-specific information to coastal managers addressing land-sea runoff.

High temporal variability of surface solar irradiance due to cloud enhancement effect over the Western Ghat mountains in peninsular India

Western Ghat (WG) mountains along the west coast of peninsular India play an important role in the distribution of monsoon rainfall on its windward and leeward sides. The study unravels the increase in cloudiness and also increase in the Cloud Enhancement of Solar irradiance (CES) during the dry and wet seasons in the windward (high altitude) and the leeward (low altitude) sides of WG. From May 2018 to May 2021, the global horizontal irradiance (GHI) reveals wide temporal and spatial variability with a high frequency of CES events, even exceeding the extraterrestrial value around the noontime during the wet season (May to October). The observed excess irradiance due to partial/transparent clouds compared to clear sky maxima is more than 400 W/m2 on the windward and 350 W/m2 on the leeward. With the increase in cloudy days, diffused irradiance also increased with greater values during CES events. CES induced positive shortwave cloud radiative forcing (CRF) varied up to +400 W/m2 (warming effect), while negative CRF varied up to −1000 W/m2 (cooling effect). During monsoon, the warming due to frequent CES events could locally offset a large cooling to some extent. Clouds resulting in huge irradiance variability in a day could also induce large fluctuations in renewable solar energy. Such short-term sporadic local events are averaged out in satellite data.

Vertical Distribution of Phytoplankton Community and Pigment Production in the Yellow Sea and the East China Sea during the Late Summer Season

Phytoplankton community structure, which plays an important role in determining productivity and food web structure, can provide important information for understanding variations in marine ecosystems under projected climate change scenarios. Rising temperatures due to climate change will increase and intensify water stratification. To understand the community composition and distribution characteristics of phytoplankton under stratified conditions, phytoplankton pigments were analyzed in the Yellow Sea (YS) and East China Sea (ECS) during the late summer season. In addition, pigment production was measured to estimate the physiological characteristics of phytoplankton relating to light, which is an essential element of photosynthesis. During our observation period, no distinct differences were found in the community composition and pigment production of phytoplankton in the YS and the ECS, but differences in the vertical distribution were observed. Overall, the dominant phytoplankton classes at the surface depth were pico-sized cyanobacteria (46.1%), whereas micro- and nano-sized diatoms (42.9%) were the abundant most classes at a 1% light depth. The major factors controlling the vertical distributions of the phytoplankton community were temperature and nutrients (i.e., nitrate and ammonium). Cyanobacteria were positively correlated with water temperature and ammonium, whereas diatoms were negatively related to water temperature and positively correlated with nitrates. Based on the pigment production, it was found that cyanobacteria at the surface layer encountered excessive irradiance conditions during the study period. The productivity of the cyanobacterial community could be decreased under high-light and high-temperature conditions. This means that cyanobacteria could have a negative influence on the quantity and quality of food available to upper trophic organisms under warmer conditions.

Photoprotective Role of Neoxanthin in Plants and Algae.

Light is a paramount parameter driving photosynthesis. However, excessive irradiance leads to the formation of reactive oxygen species that cause cell damage and hamper the growth of photosynthetic organisms. Xanthophylls are key pigments involved in the photoprotective response of plants and algae to excessive light. Of particular relevance is the operation of xanthophyll cycles (XC) leading to the formation of de-epoxidized molecules with energy dissipating capacities. Neoxanthin, found in plants and algae in two different isomeric forms, is involved in the light stress response at different levels. This xanthophyll is not directly involved in XCs and the molecular mechanisms behind its photoprotective activity are yet to be fully resolved. This review comprehensively addresses the photoprotective role of 9′-cis-neoxanthin, the most abundant neoxanthin isomer, and one of the major xanthophyll components in plants’ photosystems. The light-dependent accumulation of all-trans-neoxanthin in photosynthetic cells was identified exclusively in algae of the order Bryopsidales (Chlorophyta), that lack a functional XC. A putative photoprotective model involving all-trans-neoxanthin is discussed.

Differing photosynthetic responses to excess irradiance in the two coexisting seagrasses, Halophila ovalis and Halophila decipiens: Chloroplast avoidance movement, chlorophyll fluorescence, and leaf optical properties

Seagrasses cope with excess irradiance using a suit of photoprotective mechanisms, however, Halophila species are the only seagrasses known to exhibit chloroplast avoidance movement. Here we examined this phenomenon together with concurrent change in photosynthetic and leaf optical properties in H. ovalis and H. decipiens. Although co-existing, these two seagrasses displayed different light use characteristics derived from rapid light curves; H. ovalis and H. decipiens showed features of sun- and shade-adapted plants, respectively. Experimentally the seagrass leaves were exposed to low, medium, and high irradiance (80, 200 and 800 μmol photons m−2 s−1, respectively) for 60 min, followed by 60 min in darkness. Chloroplast movement occurred in H. ovalis exposed to medium or high irradiance and in H. decipiens exposed to low or medium irradiance. Chloroplast gathering was observed after 20 min of exposure and chloroplast dispersal was observed after 20 min in darkness, dependent on treatment and species. Increasing irradiance lowered the effective quantum yield and increased the non-photochemical quenching (NPQ). Despite stronger up-regulation in NPQ, photoinhibition was detected in H. decipiens. The absorption factor and the Soil-Plant Analysis Development value were modulated by chloroplast movement rather than a change in chlorophyll content, except for H. decipiens exposed to high irradiance where photodamage of chlorophylls may have occurred. Chloroplast movement in both seagrasses was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicating regulation by photosynthesis. Our results suggest that H. ovalis has a higher tolerance to excess irradiance than H. decipiens and that this is assisted partly by chloroplast avoidance movement.

UV Index Forecasting under the Influence of Desert Dust: Evaluation against Surface and Satellite-Retrieved Data

Human exposure to healthy doses of UV radiation is required for vitamin D synthesis, but exposure to excessive UV irradiance leads to several harmful impacts ranging from premature wrinkles to dangerous skin cancer. However, for countries located in the global dust belt, accurate estimation of the UV irradiance is challenging due to a strong impact of desert dust on incoming solar radiation. In this work, a UV Index forecasting capability is presented, specifically developed for dust-rich environments, that combines the use of ground-based measurements of broadband irradiances UVA (320–400 nm) and UVB (280–315 nm), NASA OMI Aura satellite-retrieved data and the meteorology-chemistry mesoscale model WRF-Chem. The forecasting ability of the model is evaluated for clear sky days as well as during the influence of dust storms in Doha, Qatar. The contribution of UV radiation to the total incoming global horizontal irradiance (GHI) ranges between 5% and 7% for UVA and 0.1% and 0.22% for UVB. The UVI forecasting performance of the model is quite encouraging with an absolute average error of less than 6% and a correlation coefficient of 0.93. In agreement with observations, the model predicts that the UV Index at local noontime can drop from 10–11 on clear sky days to approximately 6–7 during typical dusty conditions in the Arabian Peninsula—an effect similar to the presence of extensive cloud cover.

An uncommon intertidal record of Halophila decipiens Ostenfeld in the vicinity of mangroves

In this paper, we report the occurrence of Halophila decipiens Ostenfeld found growing in an intertidal environment. At the study site of Sungai Bahan estuary located along the Straits of Johor (Malaysia), the seagrass grew sparsely in the lower littoral zone of the mangrove coastline. Forming discontinuous patches, the seagrass was fully exposed on the mudflats during the lowest spring tides. Predictable times of exposure during low tides coincide with specific diel periods of lower light availability, which enabled avoidance of exposure to excessive irradiance. Hand-collected specimens of H. decipiens were initially defined through morphological and inflorescence characteristics. The identity of the species was confirmed based on analysis of the internal transcribed spacer sequence of its ribosomal DNA. Further analysis of this sequence demonstrated that among global populations, H. decipiens formed a sub-clade with populations from Malaysia and Australia. The colonisation by H. decipiens at the study site demonstrates its opportunistic acclimation to local environmental conditions. This discovery opens opportunities to further explore its ecology, as an instance of a less commonly studied seagrass within the region and to further investigate the unusual intertidal niche associated with the species.

Light intensity control as a strategy to improve lipid productivity in Chlorella sp. HS2 for biodiesel production

The light greatly affects the physiological properties of microalgae, but the outcome is species-specific. To improve the traits of microalgae suitable for biofuel production, we investigated the influence of the light on biomass and lipid productivity of Chlorella sp. HS2. Photosynthetic performance in terms of relative electron transport rate (rel. ETR) was maximized at 450 μmol photons m−2 s−1, which allowed cells to reach high biomass productivity of 1.10 g L−1 day−1. Although the stress was induced by excessive irradiance under 750 μmol photons m−2 s−1, Chlorella sp. HS2 was able to maintain a high growth rate and achieved higher biomass productivity (1.34 g L−1 day−1) compared to that of other Chlorella species. In an effort to understand the relationship between photosynthesis and biomass productivity, we found out that effective quantum yield [Y(II)] and rel. ETR of Chlorella sp. HS2 is relatively higher than that of Chlorella vulgaris. The total lipid content decreased as the light intensity increased at the exponential phase. Interestingly, however, this trend was reversed during the stationary phase. This implies that the high light may synergistically induce lipids when the cells undergo nutrient starvation. The lipid content and productivity continued to increase up to 0.25 g L−1 day−1 even after the light saturation point. The fraction of esterifiable lipid suitable for biodiesel production rapidly increased from 50% to 99% during the stationary phase. These results suggest that species-specific high light based cultivation can be an effective strategy to improve the lipid productivity in Chlorella sp. HS2.

Fast Repetition Rate Fluorometry (FRRF) Derived Phytoplankton Primary Productivity in the Bay of Bengal

The approach of fast repetition rate fluorometry (FRRF) requires a conversion factor (Φe : C/nPSII) to derive ecologically-relevant carbon uptake rates (PPz,t). However, the required Φe : C/nPSII is commonly measured by 14C assimilation and varies greatly across phytoplankton taxonomy and environmental conditions. Consequently, the use of FRRF to estimate gross primary productivity (GPz,t), alone or in combination with other approaches, has been restricted by both inherent conversion and procedural inconsistencies. Within this study, based on a hypothesis that the non-photochemical quenching (NPQNSV) can be used as a proxy for the variability and magnitude of Φe : C/nPSII, we thus proposed an independent field model coupling with the NPQNSV-based Φe : C/nPSII for FRRF-derived carbon, without the need for additional Φe : C/nPSII in the Bay of Bengal (BOB). Therewith, this robust algorithm was verified by the parallel measures of electron transport rates and 14C-uptake PPz,t. NPQNSV is theoretically caused by the effects of excess irradiance pressure, however, it showed a light and depth-independent response on large spatial scales of the BOB. Trends observed for the maximum quantum efficiency (Fv/Fm), the quantum efficiency of energy conversion (/) and the efficiency of charge separation (/) were similar and representative, which displayed a relative maximum at the subsurface and were collectively limited by excess irradiance. In particular, most observed values of Fv/Fm in the BOB were only about half of the values expected for nutrient replete phytoplankton. FRRF-based estimates of electron transport at PSII (ETRRCII) varied significantly, from 0.01 to 8.01 mol e− mol RCII−1 s−1, and showed profound responses to depth and irradiance across the BOB, but fitting with the logistic model. N, P, and irradiance are key environmental drivers in explaining the broad-scale variability of photosynthetic parameters. Furthermore, taxonomic shifts and physiological changes may be better predictors of photosynthetic parameters, and facilitate the selection of better adapted species to optimize photosynthetic efficiency under any particular set of ambient light condition.

Midday Depression vs. Midday Peak in Diurnal Light Interception: Contrasting Patterns at Crown and Leaf Scales in a Tropical Evergreen Tree.

Crown architecture usually is heterogeneous as a result of foraging in spatially and temporally heterogeneous light environments. Ecologists are only beginning to identify the importance of temporal heterogeneity for light acquisition in plants, especially at the diurnal scale. Crown architectural heterogeneity often leads to a diurnal variation in light interception. However, maximizing light interception during midday may not be an optimal strategy in environments with excess light. Instead, long-lived plants are expected to show crown architectures and leaf positions that meet the contrasting needs of light interception and avoidance of excess light on a diurnal basis. We expected a midday depression in the diurnal course of light interception both at the whole-crown and leaf scales, as a strategy to avoid the interception of excessive irradiance. We tested this hypothesis in a population of guava trees (Psidium guajava L.) growing in an open tropical grassland. We quantified three crown architectural traits: intra-individual heterogeneity in foliage clumping, crown openness, and leaf position angles. We estimated the diurnal course of light interception at the crown scale using hemispheric photographs, and at the leaf scale using the cosine of solar incidence. Crowns showed a midday depression in light interception, while leaves showed a midday peak. These contrasting patterns were related to architectural traits. At the crown scale, the midday depression of light interception was linked to a greater crown openness and foliage clumping in crown tops than in the lateral parts of the crown. At the leaf scale, an average inclination angle of 45° led to the midday peak in light interception, but with a huge among-leaf variation in position angles. The mismatch in diurnal course of light interception at crown and leaf scales can indicate that different processes are being optimized at each scale. These findings suggest that the diurnal course of light interception may be an important dimension of the resource acquisition strategies of long-lived woody plants. Using a temporal approach as the one applied here may improve our understanding of the diversity of crown architectures found across and within environments.

Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 586:73-89 (2018) - DOI: https://doi.org/10.3354/meps12389 Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi María Segovia1,*, M. Rosario Lorenzo1, Concepción Iñiguez1, Candela García-Gómez1,2 1Department of Ecology, Faculty of Sciences, University of Málaga, Bulevar Louis Pasteur s/n, 29071 Málaga, Spain 2Present address: Spanish Oceanographic Institute (IEO), Puerto Pesquero, 29640 Fuengirola, Málaga, Spain *Corresponding author: segovia@uma.es ABSTRACT: We exposed a natural phytoplankton community to combined present (390 µatm, low carbon [LC]) and future CO2 levels predicted for the year 2100 (900 µatm, high carbon [HC]), and ambient (4.5 nM, -DFB [desferoxamine B]) and high (12 nM, +DFB) dissolved iron (dFe) levels, for 25 d in mesocosms. We report on the physiological response of the community dominated by the coccolithophore Emiliania huxleyi. The community structure shifted on Day 10, leading to 2 different phases (1 and 2), i.e. before and after Day 10, respectively. We focussed on the massive bloom of E. huxleyi that developed in Phase 2, in the LC+DFB treatment. In high dFe conditions, pigments and photosynthetic parameters increased compared to the control (LC-DFB). Cell death was only detected during the community shift (Days 10-12) and mostly increased in the presence of high CO2. The accumulation of reactive oxygen species (ROS) decreased under high dFe, pointing to an efficient, rather than a stressed, metabolism. DNA lesions, caused by excess irradiance, were minimised under high Fe. E. huxleyi is known for its low Fe requirements for growth. However, we demonstrate that Fe is essential to E. huxleyi for DNA repair and ROS management, and to maintain optimal functioning of the photosynthetic machinery, with implications for carbon cycling and future ecosystem functioning. KEY WORDS: Mesocosms · Photosynthesis · Electron transport chain · Pigments · Cell death · Oxidative stress · DNA damage · Emiliania huxleyi Full text in pdf format Supplementary material PreviousNextCite this article as: Segovia M, Lorenzo MR, Iñiguez C, García-Gómez C (2018) Physiological stress response associated with elevated CO2 and dissolved iron in a phytoplankton community dominated by the coccolithophore Emiliania huxleyi . Mar Ecol Prog Ser 586:73-89. https://doi.org/10.3354/meps12389 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 586. Online publication date: January 11, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Illuminating the role of the Gα heterotrimeric G protein subunit, RGA1, in regulating photoprotection and photoavoidance in rice.

We studied physiological mechanisms of photoavoidance and photoprotection of a dwarf rice mutant with erect leaves, d1, in which the RGA1 gene, which encodes the Gα subunit of the heterotrimeric G protein, is non-functional. Leaves of d1 exhibit lower leaf temperature and higher photochemical reflectance index relative to wild type (WT), indicative of increased photoavoidance and more efficient light harvesting. RNA sequencing analysis of flag leaves revealed that messenger RNA levels of genes encoding heat shock proteins, enzymes associated with chlorophyll breakdown, and ROS scavengers were down-regulated in d1. By contrast, genes encoding proteins associated with light harvesting, Photosystem II, cyclic electron transport, Photosystem I, and chlorophyll biosynthesis were up-regulated in d1. Consistent with these observations, when WT and d1 plants were experimentally subjected to the same light intensity, d1 plants exhibited a greater capacity to dissipate excess irradiance (increased nonphotochemical quenching) relative to WT. The increased capacity in d1 for both photoavoidance and photoprotection reduced sustained photoinhibitory damage, as revealed by a higher Fv /Fm . We therefore propose RGA1 as a regulator of photoavoidance and photoprotection mechanisms in rice and highlight the prospect of exploiting modulation of heterotrimeric G protein signalling to increase these characteristics and improve the yield of cereals in the event of abiotic stress.

An innovative solution to the overheating problem of PV panels

Overheating of silicon PV panels due to excessive solar irradiance and high environmental temperatures is a major problem especially in the Middle East and North Africa (MENA) region. The temperature of PV panels can easily go up to 75 °C in such regions, which corresponds to a drop in efficiency of about 25%. An innovative solution is presented in this research to minimize overheating of PV panels, and that is based on natural convection. Through holes are drilled in the PV panel to assist the uprising of the hot boundary layer under the panel causing cooling of the panel. Experiments have been performed to proof the idea, and then numerical simulations are performed for further exploration of the influence of the hole size and number of holes. It was found that the temperature of the perforated PV panels is lower than the temperature of the non-perforated panels, and that temperature difference increases with increasing number of holes. However, there is a critical diameter for the hole size, such that before and after that diameter the temperature of the PV panel increases. It can be concluded from the performed research that adding through holes in the PV panel is a passive cooling technique that can minimize overheating of the panel.