Saturating Light Intensity Research Articles

224-fs soliton pulses generation at 1μm from ytterbium-doped fiber laser with CoTe2 nanosheets as an ultrafast modulator

Transition metal ditellurides (TMDTs) have numerous attractive properties, making them suitable for a wide range of applications. In this study, cobalt ditelluride (CoTe2) nanosheets, a promising TMDT for photonic applications, were prepared using an ultrasound-enhanced liquid phase exfoliation (LPE) method. A novel saturable absorber (SA) employing CoTe2 nanosheets was then fabricated by optically depositing them on microfiber. The nonlinear optical modulation properties of the CoTe2 SA were investigated. A high-performance 1 μm ultrafast fiber laser was demonstrated by incorporating newly developed CoTe2 nanosheets-based SA in a ring cavity ytterbium-doped fiber laser (YDFL). The dynamical behaviour of the proposed passively mode-locked YDFL in response to variations in pump optical power was investigated. The findings reveal that the device achieved a modulation depth of 2.5 %, and saturation light intensity of 30.6 MW/cm2. Moreover, a stable and robust mode-locked soliton optical pulse sequence with a fundamental repetition frequency of 3.089 MHz, and a pulse duration of 224 fs was generated at 1032 nm. The proposed YDFL, being all-fiber, compact, and cost-effective, is set to find extensive applications in various domains, including optical fiber communication, sensing, and biomedical imaging.

Key benthic species are affected by predicted warming in winter but show resistance to ocean acidification.

The effects of climate change on coastal biodiversity are a major concern because altered community compositions may change associated rates of ecosystem functioning and services. Whilst responses of single species or taxa have been studied extensively, it remains challenging to estimate responses to climate change across different levels of biological organisation. Studies that consider the effects of moderate realistic near-future levels of ocean warming and acidification are needed to identify and quantify the gradual responses of species to change. Also, studies including different levels of biological complexity may reveal opportunities for amelioration or facilitation under changing environmental conditions. To test experimentally for independent and combined effects of predicted near-future warming and acidification on key benthic species, we manipulated three levels of temperature (winter ambient, +0.8 and +2°C) and two levels of pco 2 (ambient at 450 ppm and elevated at 645 ppm) and quantified their effects on mussels and algae growing separately and together (to also test for inter-specific interactions). Warming increased mussel clearance and mortality rates simultaneously, which meant that total biomass peaked at +0.8°C. Surprisingly, however, no effects of elevated pco 2 were identified on mussels or algae. Moreover, when kept together, mussels and algae had mutually positive effects on each other's performance (i.e. mussel survival and condition index, mussel and algal biomass and proxies for algal productivity including relative maximum electron transport rate [rETRmax], saturating light intensity [I k] and maximum quantum yield [F v/F m]), independent of warming and acidification. Our results show that even moderate warming affected the functioning of key benthic species, and we identified a level of resistance to predicted ocean acidification. Importantly, we show that the presence of a second functional group enhanced the functioning of both groups (mussels and algae), independent of changing environmental conditions, which highlights the ecological and potential economic benefits of conserving biodiversity in marine ecosystems.

Semi-metallic PtTe2 nanosheets are used as saturable absorbers to generate passive mode-locked pulse laser in the 2 μm band

In passively modulated pulse lasers, the highly stable saturable absorber (SA) used to generate passive pulsed lasers is a necessary core device. In this paper, layered PtTe2 nanosheets were fabricated using a simple, efficient, and low-cost liquid phase exfoliation (LPE) method, and PtTe2-SA devices were prepared by spin coating. Nonlinear optical tests show that the layered PtTe2 nanosheets have good nonlinear saturable absorption characteristics in the 2 μm band, with a modulation depth of 8.2 %, a saturated light intensity of 3.72 MW/cm2, and a non-saturated loss of 9.8 %. We introduced PtTe2-SA devices into Tm3+ doped solid-state laser for the first time, achieving passive mode-locking (PML) operations. In PML operation, a short pulse output of 670.8 ps was achieved. After being exposed to the air for 20 days, it can still produce good pulse output under the same experimental device. The results show that semi-metallic PtTe2 is expected to become a highly stable SA candidate material for pulsed solid-state lasers, which can be used to generate short pulse output in the 2 μm band, providing huge production power in many fields.

Growth physiology and chlorophyll fluorescence analysis of two moss species under different LED light qualities

This study investigated the responses of Didymodon constrictus and Hypnum plumaeforme to different light qualities emitted by light-emitting diodes (LEDs), including white light (WL), red light (RL), blue light (BL), yellow light (YL), green light (GL), and a combination of red and blue light (R1B1L). The research analyzed the fluorescence imaging, photosynthetic pigments, coloration, and growth characteristics related to antioxidant enzymes in these two moss species. The results indicated that R1B1L significantly enhanced the content of photosynthetic pigments, maximum relative electron transport rate (rETRmax), saturation light intensity (IK), and the greenness of the moss. RL improved the maximum quantum yield (Fv/Fm), the light energy efficiency of H. plumaeforme and effective quantum yield in both moss species. In contrast, BL notably increased non-photochemical quenching (NPQ), photochemical quenching (qp), and the steady-state fluorescence decrease ratio (RFD) in H. plumaeforme. The application of GL significantly increases the maximum photon yield (Fv/Fm) in D. constrictus, as well as the light energy efficiency and elongation length, resulting in a shift in the color composition of both moss species towards yellow. Among the light treatments, R1B1L had the highest induction rate and promotional effect on the growth of both moss species. These mosses absorbed GL and RL effectively, while BL played a crucial role in the dissipation of heat and electron transfer in H. plumaeforme. This research provides valuable insights for the regulation of LED light environments and the physiological adaptability of moss in artificial cultivation.

Simulating short-term light responses of photosynthesis and water use efficiency in sweet sorghum under varying temperature and CO2 conditions.

Climate change, characterized by rising atmospheric CO2 levels and temperatures, poses significant challenges to global crop production. Sweet sorghum, a prominent C4 cereal extensively grown in arid areas, emerges as a promising candidate for sustainable bioenergy production. This study investigated the responses of photosynthesis and leaf-scale water use efficiency (WUE) to varying light intensity (I) in sweet sorghum under different temperature and CO2 conditions. Comparative analyses were conducted between the A n-I, g s-I, T r-I, WUEi-I, and WUEinst-I models proposed by Ye etal. and the widely utilized the non-rectangular hyperbolic (NRH) model for fitting light response curves. The Ye's models effectively replicated the light response curves of sweet sorghum, accurately capturing the diminishing intrinsic WUE (WUEi) and instantaneous WUE (WUEinst) trends with increasing I. The fitted maximum values of A n, g s, T r, WUEi, and WUEinst and their saturation light intensities closely matched observations, unlike the NRH model. Despite the NRH model demonstrating high R 2 values for A n-I, g s-I, and T r-I modelling, it returned the maximum values significantly deviating from observed values and failed to generate saturation light intensities. It also inadequately represented WUE responses to I, overestimating WUE. Across different leaf temperatures, A n, g s, and T r of sweet sorghum displayed comparable light response patterns. Elevated temperatures increased maximum A n, g s, and T r but consistently declined maximum WUEi and WUEinst. However, WUEinst declined more sharply due to the disproportionate transpiration increase over carbon assimilation. Critically, sweet sorghum A n saturated at current atmospheric CO2 levels, with no significant gains under 550 μmol mol-1. Instead, stomatal closure enhanced WUE under elevated CO2 by coordinated g s and T r reductions rather than improved carbon assimilation. Nonetheless, this response diminished under simultaneously high temperature, suggesting intricate interplay between CO2 and temperature in modulating plant responses. These findings provide valuable insights into photosynthetic dynamics of sweet sorghum, aiding predictions of yield and optimization of cultivation practices. Moreover, our methodology serves as a valuable reference for evaluating leaf photosynthesis and WUE dynamics in diverse plant species.

Unveiling the Biological Function of Phyllostachys edulis FBA6 (PeFBA6) through the Identification of the Fructose-1,6-Bisphosphate Aldolase Gene.

Fructose-1,6-bisphosphate aldolase (FBA) is a pivotal enzyme in various metabolic pathways, including glycolysis, gluconeogenesis, and the Calvin cycle. It plays a critical role in CO2 fixation. Building on previous studies on the FBA gene family in Moso bamboo, our study revealed the biological function of PeFBA6. To identify CSN5 candidate genes, this study conducted a yeast two-hybrid library screening experiment. Subsequently, the interaction between CSN5 and PeFBA6 was verified using yeast two-hybrid and LCI experiments. This investigation uncovered evidence that FBA may undergo deubiquitination to maintain glycolytic stability. To further assess the function of PeFBA6, it was overexpressed in rice. Various parameters were determined, including the light response curve, CO2 response curve, and the levels of glucose, fructose, sucrose, and starch in the leaves of overexpressing rice. The results demonstrated that overexpressed rice exhibited a higher saturation light intensity, net photosynthetic rate, maximum carboxylation rate, respiration rate, and increased levels of glucose, fructose, and starch than wild-type rice. These findings indicated that PeFBA6 not only enhanced the photoprotection ability of rice but also improved the photosynthetic carbon metabolism. Overall, this study enhanced our understanding of the function of FBA and revealed the biological function of PeFBA6, thereby providing a foundation for the development of excellent carbon fixation bamboo varieties through breeding.

Effects of summer pruning on the growth and photosynthetic characteristics of pepper (Capsicum annuum L.)

The objective of the study is to investigate the mechanism by which summer pruning enhances the growth of pepper plants, as indicated by growth and fruit appearance indicators, photosynthetic rate and gas exchange parameters, rapid light response and induction kinetics curves and the related chlorophyll fluorescence parameters. The results indicated that the leaf growth rate, the individual pepper fruit weight, and the fruit longitudinal and cross diameters of the pruned group were significantly higher than those of the control. The stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) of the pruned group were significantly higher than those of the control. The initial slope of the rapid light response curve, which represents light energy utilisation efficiency (α), the maximum electron transfer rate (Jmax) and saturated light intensity (PARsat) were all higher in the summer pruning group than in the control group. The F0 of the pruned group decreased by 16.83%, Fv/F0 increased by 23.69%, PIabs increased by 58.33%, and DIo/RC decreased by 22.09% compared to the control group. In summary, summer pruning significantly improves the leaf growth rate and fruit appearance quality of pepper, effectively promotes the photosynthesis of functional leaves, and reduces the degree of stress under adverse environmental conditions.

Addressing the long-standing limitations of double exponential and non-rectangular hyperbolic models in quantifying light-response of electron transport rates in different photosynthetic organisms under various conditions.

The models used to describe the light response of electron transport rate in photosynthesis play a crucial role in determining two key parameters i.e., the maximum electron transport rate (J max) and the saturation light intensity (I sat). However, not all models accurately fit J-I curves, and determine the values of J max and I sat. Here, three models, namely the double exponential (DE) model, the non-rectangular hyperbolic (NRH) model, and a mechanistic model developed by one of the coauthors (Z-P Ye) and his coworkers (referred to as the mechanistic model), were compared in terms of their ability to fit J-I curves and estimate J max and I sat. Here, we apply these three models to a series of previously collected Chl a fluorescence data from seven photosynthetic organisms, grown under different conditions. Our results show that the mechanistic model performed well in describing the J-I curves, regardless of whether photoinhibition/dynamic down-regulation of photosystem II (PSII) occurs. Moreover, both J max and I sat estimated by this model are in very good agreement with the measured data. On the contrary, although the DE model simulates quite well the J-I curve for the species studied, it significantly overestimates both the J max of Amaranthus hypochondriacus and the I sat of Microcystis aeruginosa grown under NH4 +-N supply. More importantly, the light intensity required to achieve the potential maximum of J (J s) estimated by this model exceeds the unexpected high value of 105 μmol photons m-2 s-1 for Triticum aestivum and A. hypochondriacus. The NRH model fails to characterize the J-I curves with dynamic down-regulation/photoinhibition for Abies alba, Oryza sativa and M. aeruginosa. In addition, this model also significantly overestimates the values of J max for T. aestivum at 21% O2 and A. hypochondriacus grown under normal condition, and significantly underestimates the values of J max for M. aeruginosa grown under NO3 -N supply. Our study provides evidence that the 'mechanistic model' is much more suitable than both the DE and NRH models in fitting the J-I curves and in estimating the photosynthetic parameters. This is a powerful tool for studying light harvesting properties and the dynamic down-regulation of PSII/photoinhibition.

Enhanced drought tolerance and photosynthetic efficiency in Arabidopsis by overexpressing phosphoenolpyruvate carboxylase from a single-cell C4 halophyte Suaeda aralocaspica.

In crop genetic improvement, the introduction of C4 plants' characteristics, known for high photosynthetic efficiency and water utilization, into C3 plants has been a significant challenge. This study investigates the effects of the desert halophyte Suaeda aralocaspica SaPEPC1 gene from a single-cell C4 photosythetic pathway, on drought resistance and photosynthetic performance in Arabidopsis. We used transgenic Arabidopsis with Zea mays ZmPEPC1 from C4 plant with classic Kranz anatomical structure and Arabidopsis AtPEPC1 from C3 photosynthetic cycle plants as controls. The results demonstrated that C4 photosynthetic-type PEPCs could improve drought resistance in plants through stomatal closure, promoting antioxidant enzyme accumulation, and reducing reactive oxygen species (ROS) accumulation. Overexpression of SaPEPC1 was significantly more effective than ZmPEPC1 in enhancing drought tolerance. Notably, overexpressed SaPEPC1 significantly improved light saturation intensity, electron transport rate (ETR), photosynthetic rate (Pn), and photoprotection ability under intense light. Furthermore, overexpression SaPEPC1 or ZmPEPC1 enhanced the activity of key C4 photosynthetic enzymes, including phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (NADP-ME), and promoted photosynthetic product sugar accumulation. However, with AtPEPC1 overexpression showing no obvious improvement effect on drought and photosynthetic performance. Therefore, these results indicated that introducing C4-type PEPC into C3 plants can significantly enhance drought resistance and photosynthetic performance. However, SaPEPC1 from a single-cell C4 cycle plant exhibits more significant effect in ETR and PSII photosynthesis performance than ZmPEPC1 from a classical C4 anatomical structure plant, although the underlying mechanism requires further exploration.

Field measurements of the carbon to chlorophyll-a ratio using Imaging FlowCytobot: Implications for dissolved oxygen modeling

In subtropical coastal waters around Hong Kong, dissolved oxygen (DO) can undergo significant diurnal changes (up to 40%–50% saturation) during algal blooms. The carbon to chlorophyll-a ratio (CCHL) – a key parameter in water quality models – is variable and depends on factors that include light intensity and temperature. Despite numerous laboratory and field investigations, the prediction of CCHL and DO during high productivity conditions remains a difficult problem; the CCHL during algal blooms has also not been measured.The phytoplankton and DO dynamics are studied in a semi-enclosed tidal inlet using a submerged Imaging FlowCytobot (IFCB) together with a real-time water quality monitoring system. A diurnal pattern of algal abundance is observed with peaks around 4pm. Based on carbon estimates from the bio-volumes of the algal images and direct measurements of chlorophyll-a, the CCHL ratio is monitored continuously during an algal bloom event. The CCHL is found to vary significantly over a bloom cycle—in the range of 10 to several hundred and generally much greater than the constant values (in the order of 10) assumed in industry standard water quality models. A first order theoretical estimate of the CCHL as a function of algal growth rate and light saturation intensity is supported by field data. Using a simple oxygen budget model, the diurnal DO changes during an algal bloom can be satisfactorily predicted by integrating IFCB data with water quality data. The findings help to improve environmental and ecosystem modeling and mariculture management.

Pulse evolution in a mode-locked erbium-doped fiber laser with a repetition rate of sub-megahertz

Mode-locked erbium-doped fiber lasers (EDFL) with the low repetition rate and high pulse energy play an important role in many fields, such as micromechanical processing, ophthalmic surgery, biological sample detection, and LiDAR detection. However, in the 1550 nm band, due to the anomalous dispersion and nonlinear effects of erbium-doped fiber lasers (EDFLs), it is difficult to achieve mode-locked pulses especially in long cavities, which brings many difficulties to engineering applications. We analyze and simulate the pulse formation and evolution process in a mode-locked EDFL at a low repetition rate of sub-megahertz. The results show that by decreasing the gain or increasing modulation depth/saturation light intensity of saturable absorber in a specific range, a stable single-pulse mode-locked state can be achieved. Then a multipulse mode-locked state can be achieved by gradually increasing the gain or decreasing the saturation light intensity. In addition, the pulse width can be compressed by adjusting the second-order dispersion coefficient. The numerical simulation results are instructive for the design and development of EDFL at a low repetition rate of sub-megahertz.

Mass ratio-dependently tunable enhancement of the optical nonlinearities of SnO2/RGO composites

The composite of graphene and semiconductor nanoparticles has attracted increasing interest in the search for novel nonlinear optical materials. Herein, composites of reduced graphene oxide (RGO) and SnO2 nanoparticles with different mass ratios were synthesized via a facile hydrothermal method. The structural morphology and basic physical properties of the SnO2/RGO composites were characterized using TEM, SEM, XRD, Raman, XPS and UV–Vis spectra, indicating that SnO2 nanoparticles were uniformly anchored on the surface of graphene nanosheets through covalent and partial-ionic bonds. The third-order optical nonlinearities of the composites were studied for the first time by the Z-scan technique using a picosecond laser at 532 nm. It was found that the composites demonstrated saturable absorption and positive nonlinear refraction properties, and both were significantly enhanced compared with pure SnO2 nanoparticles and RGO nanosheets, and the enhancement was tunable with the variation of SnO2:GO mass ratio. The maximum saturable absorption coefficient and the third-order susceptibility of the as-prepared SnO2/RGO composites were obtained to be −2.93×10–11 m W−1 and 2.25 × 10–11 esu, respectively. The maximum saturable absorption modulation depth obtained was 10% with the corresponding saturation light intensity of 0.3 GW cm−2. Moreover, the optimised third-order susceptibility of SnO2/RGO was found much greater than many other materials ever studied. Several involved factors contributing to the nonlinearities were discussed. The results propose that the third-order optical nonlinearities of SnO2/RGO and other similarly structured composites can be potentially tuned to meet certain application requirements of nonlinear optical devices by controlling the mass ratio of semiconductor to graphene.

PbSe Nanosheets for High‐Performance Harmonic Mode Locking

AbstractAs a new emerging semiconductor with interlayer bandgap, lead selenide (PbSe) have broad prospects in the fields of electrocatalysis, photocatalysis, infrared optoelectronic devices, optoelectronics, and ultrafast photonics. Among them, ultrafast photonics is receiving a lot of attention due to its ultrashort pulse, strong peak power, narrow bandwidth, and high repetition frequency. Herein, the properties are systematically studied of PbSe through various characterization methods. The modulation depth of PbSe is up to 30%, and its saturation light intensity is 7.86 MW cm−2. Using the evanescent field effect, nonlinear fiber‐based photonics devices has been successfully prepared based on the PbSe nanosheet solution, which can increase the bearable pump power. The 36th picosecond harmonic mode‐locked soliton molecule is generated in the erbium‐doped fiber laser, which corresponds to a maximum repetition frequency of 222 MHz. The results show that the signal‐to‐noise ratio can reach up to 49.1 dB which is higher than most previous works by now. The results revealed the potential of PbSe as an excellent photonics material in applications such as nonlinear optics, ultrafast photonics equipment, photoconductive detectors, and light modulators.

Total Phenolic Content, Biomass Composition, and Antioxidant Activity of Selected Marine Microalgal Species with Potential as Aquaculture Feed.

There has been growing interest in microalgal biomolecules for health and cosmetics, as well as in the use of microalgae as aquaculture feed due to the need to replace fishmeal and fish oil with sustainable yet equally nutritious alternatives. Aim of this study is to evaluate the potential of five marine microalgal species, namely Chlorella minutissima, Dunaliella salina, Isochrysis galbana, Nannochloropsis oculata and Tisochrysis lutea, for the co-production of antioxidants and aquaculture feed. Batch cultivation was performed under saturating light intensity and continuous aeration. Freeze-dried biomass was extracted sequentially with water and methanol and evaluated for phenolic content and antioxidant activity, as well as proximate composition and fatty acid profile. Methanolic extracts of C. minutissima presented the highest phenolic content, measured with the Folin–Ciocalteu assay, and antioxidant activity. However, HPLC and LC-MS showed the presence of non-pigment compounds only in T. lutea. Total phenolic content and antioxidant activity were correlated to chlorophyll content. N. oculata and T. lutea were rich in eicosapentaenoic acid and docosahexaenoic acid, respectively, as well as in protein. In conclusion, N. oculata and T. lutea are suitable candidates for further optimization, while the data presented suggest that pigment effects on the Folin–Ciocalteu method require reconsideration.

Could black anti-hail net have an extra role as an amelioration agent against heat stress in kiwifruit?

BACKGROUND: Kiwifruit plants are extremely sensitive to hail storms. Black anti-hail nets are the most frequently used in kiwifruit culture, to protect both the plant and current as well as future production. OBJECTIVE: The present trial aimed to assess if the black hail net could also serve as an amelioration agent against high temperature and irradiance during the summer months. METHODS: The photosynthetic capacity, the yield, and fruit quality (carbohydrates, organic acids, phenolic compounds, and antioxidant capacity) of “Hayward” kiwifruit cultivar, both at harvest and after three months of storage were evaluated. RESULTS: Photosynthetic capacity under the net was slightly higher compared to control, while leaf temperature was always lower during the summer and autumn. The yield was significantly enhanced under the net, while the fruits exhibited higher titratable acidity, organic acids, and ascorbic acid concentration. After the storage, fruits produced from vines grown under net still had higher organic acid content, as well as total soluble solids but lower antioxidant capacity compared to control. CONCLUSIONS: Net installation above kiwifruit canopy seems to alleviate the effects of high temperature and heat load on kiwifruit vines, under saturating light intensity, inducing higher yields with good fruit quality.

Spatial and Temporal Variations of Chlorophyll a and Primary Productivity in the Hangzhou Bay

The Hangzhou Bay (HZB) is an important part of the Zhoushan fishing ground, the most productive region in the Eastern China Seas. Although HZB remains eutrophication all year round, its chlorophyll a (Chl) and primary productivity (PP) are usually significantly lower than those in the adjacent waters. In the present study, we presented the Chl and PP distributions in the HZB and analyzed their correlations with environmental factors in four seasons. The field observation showed that Chl and PP had significant seasonal variations, and was highest in the summer (1.66 ± 0.61 mg·m−3 and 12.11 ± 12.25 mg C·m−3·h−1, respectively). Total suspended matters (TSM) concentration was the key environmental factor that constrains PP in the study area. High concentration of TSM reduced light exposure (LE, the annual mean value was 0.92 ± 0.81 Einstein·m−2·day−1) in the mixed layer of the HZB, which was much lower than the saturated light intensity of phytoplankton growth, and thus caused a strong light limitation in the HZB. However, the seasonal variations in the photosynthesis rates (PB) and Chl did not coincide. This fact suggested that the growth rate was not the only factor controlling seasonal variations of phytoplankton biomass. In winter, the very high TSM and strong mixing might reduce the zooplankton grazing rate, and lead to a relatively high concentration of Chl during the very low LE and PB period. These results implied that, in the HZB, the extremely turbid water could affect both phytoplankton growth and loss, which was probably the major mechanism responsible for the complex phytoplankton spatial and temporal variations.

Toward bio‐optical phenotyping of reef‐forming corals using Light‐Induced FluorescenceTransient‐FastRepetition Rate fluorometry

AbstractActive chlorophyllafluorometry is a well‐established tool for noninvasively diagnosing coral functional state, but has not yet been developed as a rapid phenotyping (functional screening) platform as for agriculture and forestry. Here, we present a proof‐of‐concept using Light‐Induced Fluorescence Transient‐Fast Repetition Rate fluorometry (LIFT‐FRRf) to identify coral photobiological‐based phenotypes in the context of rapidly scaling coral propagation practices on the northern Great Barrier Reef. For example, resolving light niche plasticity to inform transplantation, and identifying functionally diverse colonies to maximize stock selection. We first used optically diverse laboratory‐reared corals and coral endosymbiont (Symbiodiniaceae) isolates to develop a phenotyping approach integrating FRRf instantaneous kinetic parameters (light harvesting, electron turnover rates) and light‐dependent parameters (dynamic “quenching” terms, saturating light intensity [EK]). Subsequent field‐based LIFT‐FRRf phenotyping of coral from a selective (2‐4 m depth) reef habitat revealed that widely topographically dispersed platingAcroporataxa exhibited broad light niche plasticity (EKvariance) underpinned by multiple phenotypes that were predominantly differentiated by minimum electron turnover capacity; fluorometer configurations that cannot resolve kinetic parameters will thus likely have more limited capacity to resolve phenotypes. As such, platingAcroporahave broad propagation potential in terms of multiple functional variants for stock and across diverse light environments (growth, transplantation). In contrast, coral taxa (Pocillopora verrucosa,Echinopora lamellosa) with relatively restricted topographic dispersion exhibited less light niche plasticity and only single phenotypes, thereby imposing more constraints for propagation. We discuss the core technical, operational, and conceptual steps required to develop more sophisticated coral phenotyping platforms.

Barley Genotypes Vary in Stomatal Responsiveness to Light and CO2 Conditions.

Changes in stomatal conductance and density allow plants to acclimate to changing environmental conditions. In the present paper, the influence of atmospheric CO2 concentration and light intensity on stomata were investigated for two barley genotypes—Barke and Bojos, differing in their sensitivity to oxidative stress and phenolic acid profiles. A novel approach for stomatal density analysis was used—a pair of convolution neural networks were developed to automatically identify and count stomata on epidermal micrographs. Stomatal density in barley was influenced by genotype, as well as by light and CO2 conditions. Low CO2 conditions resulted in increased stomatal density, although differences between ambient and elevated CO2 were not significant. High light intensity increased stomatal density compared to low light intensity in both barley varieties and all CO2 treatments. Changes in stomatal conductance were also measured alongside the accumulation of pentoses, hexoses, disaccharides, and abscisic acid detected by liquid chromatography coupled with mass spectrometry. High light increased the accumulation of all sugars and reduced abscisic acid levels. Abscisic acid was influenced by all factors—light, CO2, and genotype—in combination. Differences were discovered between the two barley varieties: oxidative stress sensitive Barke demonstrated higher stomatal density, but lower conductance and better water use efficiency (WUE) than oxidative stress resistant Bojos at saturating light intensity. Barke also showed greater variability between treatments in measurements of stomatal density, sugar accumulation, and abscisic levels, implying that it may be more responsive to environmental drivers influencing water relations in the plant.

Heatwave Effects on the Photosynthesis and Antioxidant Activity of the Seagrass Cymodocea nodosa under Contrasting Light Regimes

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.

Leaf Phenological Stages of Winter Oilseed Rape (Brassica napus L.) Have Conserved Photosynthetic Efficiencies but Contrasted Intrinsic Water Use Efficiencies at High Light Intensities.

Leaf senescence in source leaves leads to the active degradation of chloroplast components [photosystems, chlorophylls, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)] and plays a key role in the efficient remobilization of nutrients toward sink tissues. However, the progression of leaf senescence can differentially modify the photosynthetic properties of source leaves depending on plant species. In this study, the photosynthetic and respiratory properties of four leaf ranks of oilseed rape describing leaf phenological stages having different sink-source activities were analyzed. To achieve this, photosynthetic pigments, total soluble proteins, Rubisco amounts, and the light response of chlorophyll fluorescence parameters coupled to leaf gas exchanges and leaf water content were measured. Photosynthetic CO2 assimilation and electron transfer rates, Rubisco and chlorophyll levels per leaf area were gradually decreased between young, mature and senescent leaves but they remained highly correlated at saturating light intensities. However, senescent leaves of oilseed rape had a lower intrinsic water use efficiency compared to young and mature leaves at saturating light intensities that was mainly due to higher stomatal conductance and transpiration rate with respect to stomatal density and net CO2 assimilation. The results are in favor of a concerted degradation of chloroplast components but a contrasted regulation of water status between leaves of different phenological stages of winter oilseed rape.