Maximum Quantum Efficiency Of Photosystem Research Articles

Short-term thermal acclimation improved the thermal tolerance of three species of scleractinian corals in the South China Sea

Investigating the potential and mechanisms of thermal adaptability in scleractinian corals is critical for aiding corals in dealing with global warming and improving the efficiency of coral reef restoration efforts. Although thermal acclimation facilitates the resistance of branching corals to thermal stress, little is known about the physiological processes of massive and platy corals in the South China Sea or their ability to adapt to heat stress. In this study, we conducted indoor short-term thermal acclimation simulation experiments on three types of corals: massive Porites lutea, platy Pavona decussata, and branching Pocillopora damicornis. Subsequently, we studied the responses and adaptive mechanisms of the three corals to heat stress and explored the effects of short-term thermal acclimation using physiological and biochemical markers. The results showed that the three corals exhibited comparable phenotypic and physiological responses to heat stress, including tentacle retraction and decreases in zooxanthellae density, maximum quantum efficiency of photosystem II, and glutathione content, along with increases in antioxidant activity (catalase and superoxide dismutase), ammonium assimilation (glutamine synthetase), and apoptosis (lipid peroxide and caspase-3). Additionally, heat tolerance differed among the different species of coral. Furthermore, the physiological markers performed better in all three coral types after acclimation, and the effects of short-term acclimation decreased from P. lutea to P. damicornis to P. decussata. We propose that short-term thermal acclimation enhances the heat tolerance of corals by affecting their metabolism and antioxidant capacity. Leveraging short-term thermal acclimation in coral reef restoration efforts could help corals adapt to the threats posed by global warming and enhance restoration efficiency.

Стрессорное воздействие биоцидных метаболитов актинобактерии Streptomyces geldanamycininus Z374 на цианобактерии Microcystis aeruginosa

Over the past decades, as a result of anthropogenic pollution and global warming, the frequency, intensity and geographical distribution of the mass development of microalgae and cyanobacteria in water bodies have significantly increased. The Microcystis species are responsible for most cases of the cyanobacterial blooms in freshwater bodies worldwide. Microcystis aeruginosa is the most commonly observed of them. In this work, we assessed the stress effect of isolated from actinobacteria Streptomyces geldanamycininus cyanocidal crude biocide Z374 (CB Z374) on the cyanobacteria M. aeruginosa. The results showed that CB Z374 significantly inhibited M. aeruginosa biomass. The CB Z374 half maximal effective concentration (EC50) for M. aeruginosa after 96 hours of treatment was 5 mg/L. The growth of M. aeruginosa with CB Z374 is characterized by an increase in the duration of the lag-phase, a decrease in the specific growth rate and biomass yield compared to the control. CB Z374 caused oxidative stress in cyanobacteria cells, determined by the elevated levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) up to 1.6 times, as well as an increased permeability of M. aeruginosa cell membranes by 1.5 times. The levels of superoxide dismutase (SOD) and catalase (CAT) activities and reduced glutathione (GSH) content raised in response to oxidative stress. M. aeruginosa growth inhibition was accompanied by a photosynthesis modification: the photosynthetic pigments phycobiliproteins and carotenoids content increases by 2.3 and 1.6 times respectively and the chlorophyll a content decreases by 1.2 times. CB Z374 inhibited M. aeruginosa photosynthesis, which was expressed in a decline in the maximum quantum efficiency of photosystem II – Fv/Fm by 10% and a reduction in the electron transfer rate (ETR) by 18%. We assume that oxidative stress and, as a result, cell membranes damage and photosynthesis inhibition are the main mechanisms of the cyanocidal action of CB Z374 on M. aeruginosa.

Mapping the genetic architecture of low-temperature stress tolerance in citron watermelon.

Sweet-fleshed watermelon (Citrullus lanatus) is an important vegetable crop of the tropical origin. It is widely grown and consumed around the world for its hydration and nutritional quality values. Low-temperature stress can affect early planting, seedling establishment, and expansion of crop production to new areas. A collection of 122 citron watermelon (Citrullus amarus) accessions were obtained from the USDA's National Plant Germplasm Repository System gene bank in Griffin, GA. The accessions were genotyped using whole genome resequencing to generate single nucleotide polymorphisms (SNPs) molecular markers and screened under cold-stressed and non-stressed control conditions. Four low-temperature stress tolerance related traits including shoot biomass, vine length, maximum quantum efficiency of photosystem II, and chlorophyll content were measured under cold-stressed and non-stressed control treatment conditions. Correlation analysis revealed the presence of positive relationships among traits. Broad-sense heritability for all traits ranged from 0.35 to 0.73, implying the presence of genetic contributions to the observed phenotypic variation. Genomic regions underlying these traits across several citron watermelon chromosomes were identified. Four low-temperature stress tolerance related putative candidate genes co-located with the peak SNPs from genome-wide association study. These genomic regions and marker information could potentially be used in molecular breeding to accelerate genetic improvements for low-temperature stress tolerance in watermelon.

Foliar application of pyroligneous acid acts synergistically with fertilizer to improve the productivity and phytochemical properties of greenhouse-grown tomato

Pyroligneous acid (PA) is rich in bioactive compounds and known to have the potential to improve crop productivity and phytochemical content. However, the synergistic effect of PA and fertilizer has not been thoroughly studied. In this study, we assessed the biostimulatory effect of different rates of foliar PA application (i.e., 0, 0.25, 0.5, 1, and 2% PA/ddH2O (v/v)) combined with full rate (i.e., 0.63, 0.28, 1.03 g) and half rate of nitrogen-phosphorus-potassium (NPK) fertilizer on the yield and nutritional quality of greenhouse-grown tomato (Solanum lycopersicum ‘Scotia’). Plants treated with 0.25% and 0.5% PA showed a significantly (p < 0.001) higher maximum quantum efficiency of photosystem II (Fv/Fm) and increased potential photosynthetic capacity (Fv/Fo), especially when combined with the full NPK rate. Leaf chlorophyll was significantly (p < 0.001) increased by approximately 0.60 and 0.49 folds in plants treated with 2% PA and full NPK rate compared to no spray and water, respectively. Total number of fruits was significantly (p < 0.001) increased by approximately 0.56 folds with the 2% PA irrespective of the NPK rate. The combined 2% PA and full NPK rate enhanced total fruit weight and the number of marketable fruits. Similarly, fruit protein, sugar and 2,2-diphenyl-1-picrylhydrazyl (DPPH) activity were significantly (p < 0.001) enhanced by the combined 2% PA and full NPK rate. In contrast, the 0.5% PA combined with half NPK rate increased fruit carotenoid and phenolic contents while the 2% PA plus half NPK rate enhanced fruit flavonoid content. Generally, the synergistic effect of PA and NPK fertilizer increased fruit elemental composition. These showed that foliar application of 2% PA with full NPK rate is the best treatment combination that can be adopted as a novel strategy to increase the productivity and quality of tomato fruits. However, further study is required to investigate the molecular basis of PA biostimulatory effect on plants.

Early detection of Kentucky bluegrass and perennial ryegrass responses to drought stress by measuring chlorophyll fluorescence parameters

AbstractKentucky bluegrass (Poa pratensis L.; drought resistant) and perennial ryegrass (Lolium perenne L.; drought sensitive) are economically important grass species contrasting in drought stress resistance. This study determined the optimal chlorophyll fluorescence parameters to indicate drought incidence and whether the parameters differentiate intra‐ and interspecies variations in drought stress. For each species, nine cultivars were exposed to well‐watered or drought (water withheld) conditions in growth chambers containing high‐throughput photosynthetic imagers to track real‐time responses of maximum quantum efficiency of photosystem II (Fv/Fm), quantum yield of photosystem II (ΦII), non‐photochemical quenching (NPQ), energy‐dependent quenching (qE), and photoinhibition‐associated quenching (qI). Soil moisture content and relative water content of leaf tissues were evaluated. Due to drought, Fv/Fm and ΦII decreased for cultivars of both species but earlier for perennial ryegrass compared to Kentucky bluegrass. The NPQ, qI, and qE values exhibited more dynamic and earlier changes due to drought compared to Fv/Fm and ΦII and allowed for early, mid, and late drought responses to be illustrated. Drought induced an increase in NPQ, qI, and qE values, which corresponded to activation of photoprotection mechanisms, and was exhibited earlier for perennial ryegrass compared to Kentucky bluegrass. As the drought treatment progressed, a decrease or stabilization of low values of NPQ, qI, and qE was observed, and the lowest values were associated with the most drought‐sensitive cultivars. These results indicate important stress tolerance protection mechanisms for grass species and will broadly impact basic and applied grass research as a nondestructive phenotyping tool.

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Elevated atmospheric CO2 concentration mitigates salt damages to safflower: Evidence from physiological and biochemical examinations

The physiological and biochemical responses of salt-stressed safflower to elevated CO2 remain inadequately known. This study investigated the interactive effects of high CO2 concentration (700 ± 50 vs. 400 ± 50 μmol mol−1) and salinity stress levels (0.4, 6, and 12 dS m−1, NaCl) on growth and physiological properties of four safflower (Carthamus tinctorius L.) genotypes, under open chamber conditions. Results showed that the effects of CO2 on biomass of shoot and grains depend on salt stress and plant genotype. Elevated CO2 conditions increased shoot dry weight under moderate salinity stress and decreased it under severe stress. The increased CO2 concentration also increased the safflower genotypes' relative water content and their K+/Na + concentrations. Also enriched CO2 increased total carotenoid levels in safflower genotypes and improved membrane stability index by reducing H2O2 levels. In addition, increased CO2 level led to an increase in seed oil content, under both saline and non-saline conditions. This effect was particularly pronounced under severe saline conditions. Under conditions of high CO2 and salinity, the Koseh genotype exhibited higher grain weight and seed oil content than other genotypes. This advantage is due to the higher relative water content, maximum quantum efficiency of photosystem II (Fv/Fm), and K+/Na+, as well as the lower Na+ and H2O2 concentrations. Results indicate that the high CO2 level mitigated the destructive effect of salinity on safflower growth by reducing Na + uptake and increasing the Fv/Fm, total soluble carbohydrates, and membrane stability index. This finding can be used in safflower breeding programs to develop cultivars that can thrive in arid regions with changing climatic conditions.

Nonuniform salinity regulate leaf characteristics and improve photosynthesis of cherry tomatoes under high salinity

Cherry tomato (Lycopersicon esculentum var. cerasiforme) is a relatively salt-tolerant fruit and vegetable widely planted worldwide. In this study, the growth and physiological responses and the different regulatory of cherry tomatoes under high, low salinity, and partial root zone salinity conditions were investigated. Cherry tomatoes grown under nonuniform salinity (0/20, 0/100 mM NaCl) conditions in a split-root pot were compared with seedlings grown under uniform salinity (20, 100 mM NaCl) conditions, and their growth and physiological parameters were determined. Our results showed that the growth was not hindered under a low salinity (20 mM NaCl), and the fruit quality was improved without a yield reduction; this was caused by promoted root growth and better leaf function maintenance. The relief effects under the higher salt stress (100 mM NaCl) conditions were more significant than those under a lower salt stress condition (20 mM NaCl). Compared with uniform high salinity conditions, nonuniform salinity conditions could improve photosynthetic characteristics and maintain better leaf function. The apparent quantum efficiency (AQE), carboxylation efficiency (CE) and light saturation irradiance (LSP) increased, while the light compensation point (LCP) and CO2 compensation point (CCP) decreased; this enhanced the light energy and CO2 utilization. Chlorophyll content (Chl), including Chl a and b and the carotenoids (Car), and the chlorophyll fluorescence parameters, including the maximum quantum efficiency of photosystem II (PSII) reaction centers (Fv/Fm), the quantum efficiency of PSII (Y(II)) and electron transport rate through PSII (ETR), were increased; this significantly promoted the net photosynthetic rate (Pn) and water use efficiency (WUE). Compared with a uniform high salt stress treatment, the leaf relative water content (RWC) and water potential (Ψ) increased by 22.57% and 13.71%, respectively, the electrolyte leakage rate decreased by 36.13%, and the final yield increased by 2.89 times under a nonuniform high salinity treatment. These results indicated that nonuniform salinity conditions regulated the leaf water relations and the antioxidant system and maintained better anatomical structure to improve photosynthesis in cherry tomato under a high salinity environment. Finally, our results can aid in the improvement of tomato productivity from salt-affected lands.

Analysis of double phytoextraction of Cadmium and microplastics by Galinsoga Quadriradiata in soil An exploration for a comprehensive treatment method for the environment

The wide usage of microplastics and heavy metals has led to the accumulation of these pollutants in our environment. Among heavy metals and microplastics, Cadmium (Cd), polyvinyl chloride (PVC), and polyethylene (PE) are the most severe and ubiquitous pollutants. With large surface areas, microplastics have the ability to absorb metal ions, potentially performing "carrier effect", by which microparticles enhance the transfer of other pollutants from soil to plants. Phytoextraction has been shown to be the most effective strategy to remediate heavy metal contamination. In this study, we selected Galinsoga quadriradiata (G. quadriradiata) as the test species to investigate the effectiveness of phytoextraction in soil contaminated with Cd, PVC and PE. According to our results, G. quadriradiata present effective phytoextraction to Cd and microplastics. However, the carrier effect between Cd and PVC or PE only exists in the value of maximal quantum efficiency of photosystem II (Fv/Fm) but has no effect on the uptake of Cd by G. quadriradiata. For future studies, we propose to investigate the carrier effect between heavy metals and microplastics in plants, test the pathway of microplastics by which they are up-taken by plants from soil, and increase the efficiency of phytoextraction by exposing plants (such as G. quadriradiata) that have been proved to absorb heavy metal to microplastics.

Natural variation of temperature acclimation of Arabidopsis thaliana.

Acclimation is a multigenic trait by which plants adjust photosynthesis and metabolism to cope with a changing environment. Here, natural variations of photosynthetic efficiency and acclimation of the central carbohydrate metabolism were analyzed in response to low and elevated temperatures. For this, 18 natural accessions of Arabidopsis thaliana, originating from Cape Verde Islands and Europe, were grown at 22°C before being exposed to 4°C and 34°C for cold and heat acclimation, respectively. Absolute amounts of carbohydrates were quantified together with their subcellular distribution across plastids, cytosol and vacuole. Linear electron transport rates (ETRs) were determined together with the maximum quantum efficiency of photosystem II (Fv/Fm) for all growth conditions and under temperature fluctuation. Under elevated temperature, ETR residuals under increasing photosynthetic photon flux densities significantly correlated with the degree of temperature fluctuation at the original habitat of accessions, indicating a geographical east/west gradient of photosynthetic acclimation capacities. Plastidial sucrose concentrations positively correlated with maximal ETRs under fluctuating temperature, indicating a stabilizing role within the chloroplast. Our findings revealed specific subcellular carbohydrate distributions that contribute differentially to the photosynthetic efficiency of natural Arabidopsis thaliana accessions across a longitudinal gradient. This sheds light on the relevance of subcellular metabolic regulation for photosynthetic performance in a fluctuating environment and supports the physiological interpretation of naturally occurring genetic variation of temperature tolerance and acclimation.

Validating and Developing Hyperspectral Indices for Tracing Leaf Chlorophyll Fluorescence Parameters under Varying Light Conditions

Chlorophyll a fluorescence (ChlFa) parameters provide insight into the physiological and biochemical processes of plants and have been widely applied to monitor and evaluate the photochemical process and photosynthetic capacity of plants in a variety of environments. Recent advances in remote sensing provide new opportunities for the detection of ChlFa at large scales but demand further tremendous efforts. Among such efforts, application of the hyperspectral index is always possible, but the performance of hyperspectral indices in detecting ChlFa parameters under varying light conditions is much less investigated. The objective of this study is to investigate the performance of reported hyperspectral indices for tracking ChlFa parameters under different light conditions and to develop and evaluate novel spectral indices. Therefore, an experiment was conducted to simultaneously measure ChlFa parameters and spectral reflectance of sunlit and shaded leaves under varying light conditions, and 28 reported hyperspectral indices were examined for their performance in tracking the ChlFa parameters. Furthermore, we developed novel hyperspectral indices based on various spectral transformations. The results indicated that the maximum quantum efficiency of photosystem II (PSIImax), the cumulative quantum yield of photochemistry (ΦP), and the fraction of open reaction centers in photosystem II (qL) of sunlit leaves were significantly higher than those of shaded leaves, while the cumulative quantum yield of regulated thermal dissipation (ΦN) and fluorescence (ΦF) of shaded leaves was higher than that of sunlit leaves. Efficient tracing of ChlFa parameters could not be achieved from previously published spectral indices. In comparison, all ChlFa parameters were well quantified in shaded leaves when using novel hyperspectral indices, although the hyperspectral indices for tracing the non-photochemical quenching (NPQ) and ΦF were not stable, especially for sunlit leaves. Our findings justify the use of hyperspectral indices as a practical approach to estimating ChlFa parameters. However, caution should be used when using spectral indices to track ChlFa parameters based on the differences in sunlit and shaded leaves.

Red-Light Transmittance Changes in Variegated Pelargonium zonale-Diurnal Variation in Chloroplast Movement and Photosystem II Efficiency.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark-light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

Investigating physiological responses of Wild Rocket subjected to artificial Ultraviolet B irradiation

Utilization of ultraviolet-B radiation (UV-B) is a way to encourage the accumulation of phytochemicals such as glucosinolates, carotenoids, phenolics and flavonoids in plants. In the current research, UV-B treatments were performed, as a possible elicitation strategy to promote the secondary metabolites accumulation in wild rocket (Diplotaxis tenuifolia (L.) DC). After performing the destructive analysis, it has been found that the concentration of chlorophyl a and b as well as carotenoids decreased in response to the UV-B stress. Thiobarbituric acid reactive substances (TBARS) assay has been performed to investigate the membranes damage caused by the UV-B radiation. The analyses confirmed that the highest UV-B tested dose induced the greater damage. Interestingly, an increase of phenolic index, and an accumulation of anthocyanins and glucosinolates has been recorded under the successive exposure of varying UV-B doses. The total sugars, reducing sugars and sucrose buildup were also remarkable. Non-destructive analysis revealed a decline in the overall performance of the UV-B treated plants as well as the maximum quantum efficiency of photosystem II. A decrease in the chlorophyll estimates while an enhanced flavanols and anthocyanins were observed through non-destructive readings. Results of this study not only provided a feasible UV-B dose selection and supplementation for the wild rocket but also the understanding about enhanced phytochemical accumulation in plants against UV-B stress.

Individual and combined effects of herbicide prometryn and nitrate enrichment at environmentally relevant concentrations on photosynthesis, oxidative stress, and endosymbiont community diversity of coral Acropora hyacinthus

Nitrogen pollution and pesticides such as photosystem II (PSII) inhibitor herbicides have several detrimental impacts on coral reefs, including breakdown of the symbiosis between host corals and photosynthetic symbionts. Although nitrogen and PSII herbicide pollution separately cause coral bleaching, the combined effects of these stressors at environmentally relevant concentrations on corals have not been assessed. Here, we report the combined effects of nitrate enrichment and PSII herbicide (prometryn) exposure on photosynthesis, oxidative status and endosymbiont community diversity of the reef-building coral Acropora hyacinthus. Coral fragments were exposed in a mesocosm system to nitrate enrichment (9 μmol/L) and two prometryn concentrations (1 and 5 μg/L). The results showed that sustained prometryn exposure in combination with nitrate enrichment stress had significant detrimental impacts on photosynthetic apparatus [the maximum quantum efficiency of photosystem II (Fv/Fm), nonphotochemical quenching (NPQ) and oxidative status in the short term. Nevertheless, the adaptive mechanism of corals allowed the normal physiological state to be recovered following 1 μg/L prometryn and 9 μmol/L nitrate enrichment individual exposure. Moreover, exposure for 9 days was insufficient to trigger a shift in Symbiodiniaceae community. Most importantly, the negative impact of exposure to the combined environmental concentrations of 1 μg/L prometryn and 9 μmol/L nitrate enrichment was found to be significantly greater on the Fv/Fm, quantum yield of non-regulated energy dissipation [Y(NO)], NPQ, and oxidative status of corals compared to the impact of individual stressors. Our results show that interactions between prometryn stress and nitrate enrichment have a synergistic impact on the photosynthetic and oxidative stress responses of corals. This study provides valuable insights into combined effects of nitrate enrichment and PSII herbicides pollution for coral's physiology. Environmental concentrations of PSII herbicides may be more harmful to photosystems and antioxidant systems of corals under nitrate enrichment stress. Thus, future research and management of seawater quality stressors should consider combined impacts on corals rather than just the impacts of individual stressors alone.

Effect of UV-B elicitation on spearmint’s (Mentha spicata L.) morpho-physiological traits and secondary metabolites production

Abstract Additional artificial ultraviolet-B irradiation (UV-B) is a substitute for the natural UV-B radiation, which is believed to modulate the antioxidants production in plants against the abiotic stress. The present research was formulated by using an indoor UV-B chamber, capable of irradiating UV-B at single wavelength of 315 nm on spearmint. In vitro destructive analysis revealed the reduction in accumulation of chlorophyll a and b as well as carotenoids. However, an elevated levels of phenolic index and total anthocyanins were recorded for both 43.2 KJ/m2 and 86.4 KJ/m2 UV-B doses. TBARS assay was carried out to record the lipid peroxidation in the spearmint and likewise, an enhanced secondary metabolites production, an increased lipid peroxidation was seen with the successive increased in the UV–B doses. A remarkable accumulation in the total sugars, reducing sugars and sucrose were also noticed. In vivo analysis revealed a decrease in chlorophyll estimated values as well as an increase of flavanols. Overall leaf fluorescence performance index was improved under both UV-B doses as well as the maximum quantum efficiency of photosystem II. Decreases in the total yield, plant height and length of internode was observed for both UV-B doses however, an enhanced number of stems was recorded for the 43.2 KJ/m2 UV-B dose. The results of present study not only provided a clear indication of the potential of UV-B in modifying the phytochemicals accumulation in plants but also opened a room for investigating various indoor UV-B doses for future studies of plants and their interaction towards UV-B. Graphical Abstract

Trocas gasosas e eficiência fotoquímica de goiabeira irrigada com águas salinas e adubação nitrogenada-potássica

ABSTRACT The objective of this study was to evaluate the effects of different combinations of nitrogen and potassium fertilization on gas exchange and chlorophyll a fluorescence in seedlings of guava cv. Paluma irrigated with water of different salinity levels. The experiment was set up in a randomized block design and analyzed in 5 × 4 factorial scheme, with four replicates. The treatments were composed of the combination of the factor electrical conductivity of irrigation water - ECw (0.3, 1.1, 1.9, 2.7, and 3.5 dS m-1), with the factor combinations (C) formed from recommended doses of nitrogen (N) and potassium (K2O), 70% N + 50% K2O, 100% N + 75% K2O, 130% N + 100% K2O, and 160% N + 125% K2O. The fertilization combination 130% N + 100% K2O mitigated the effects of salt stress up to mean ECw of 1.3 dS m-1, resulting in increments in CO2 assimilation rate, transpiration, instantaneous carboxylation efficiency, and electron transport rate. For maximum quantum efficiency of photosystem II, only treatment irrigated with ECw 3.5 dS m-1 under the combination 160% N + 125% K2O showed damage to the photosynthetic apparatus.

Combined Effects of the Training Method and Deficit Irrigation on the Yield and Fruit Quality of Semi-Determinate Cherry Tomato (&lt;i&gt;Solanum lycopersicum&lt;/i&gt; L.)

Deficit irrigation can be used to improve tomato fruit quality. The semi-determinate tomato behaves like a bush tomato, with lateral shoots providing additional vegetative growth, but the response to deficit irrigation and the suitable training method have not been properly understood. Therefore, we clarify the combined effect of a training method (non-training, which omits manual plant management such as lateral shoot removal) and deficit irrigation (30–36% of field capacity) on yield, growth, and fruit quality of semi-determinate cherry tomato. Although deficit irrigation influenced non-training plants more than single-training plants (a conventional method by removing all lateral shoots) owing to the lowest midday leaf water potential, both plants showed the same levels of maximum quantum efficiency of photosystem II and fruit yield under deficit irrigation. Furthermore, non-training plants produced the highest levels of total soluble solids, glucose, fructose, citric acid, malic acid, and ascorbic acid under deficit irrigation. These observations indicated that the increased concentrations of the abovementioned components occurred as a result of water shortage in the fruit when compared with single-training plants. We conclude that non-training is suitable for semi-determinate cherry tomato cultivation under deficit irrigation, and that this method can produce high-quality fruits while mitigating manual plant management.

Estimation of Fv/Fm in Spring Wheat Using UAV-Based Multispectral and RGB Imagery with Multiple Machine Learning Methods

The maximum quantum efficiency of photosystem II (Fv/Fm) is a widely used indicator of photosynthetic health in plants. Remote sensing of Fv/Fm using MS (multispectral) and RGB imagery has the potential to enable high-throughput screening of plant health in agricultural and ecological applications. This study aimed to estimate Fv/Fm in spring wheat at an experimental base in Hanghou County, Inner Mongolia, from 2020 to 2021. RGB and MS images were obtained at the wheat flowering stage using a Da-Jiang Phantom 4 multispectral drone. A total of 51 vegetation indices were constructed, and the measured Fv/Fm of wheat on the ground was obtained simultaneously using a Handy PEA plant efficiency analyzer. The performance of 26 machine learning algorithms for estimating Fv/Fm using RGB and multispectral imagery was compared. The findings revealed that a majority of the multispectral vegetation indices and approximately half of the RGB vegetation indices demonstrated a strong correlation with Fv/Fm, as evidenced by an absolute correlation coefficient greater than 0.75. The Gradient Boosting Regressor (GBR) was the optimal estimation model for RGB, with the important features being RGBVI and ExR. The Huber model was the optimal estimation model for MS, with the important feature being MSAVI2. The Automatic Relevance Determination (ARD) was the optimal estimation model for the combination (RGB + MS), with the important features being SIPI, ExR, and VEG. The highest accuracy was achieved using the ARD model for estimating Fv/Fm with RGB + MS vegetation indices on the test sets (Test set MAE = 0.019, MSE = 0.001, RMSE = 0.024, R2 = 0.925, RMSLE = 0.014, MAPE = 0.026). The combined analysis suggests that extracting vegetation indices (SIPI, ExR, and VEG) from RGB and MS remote images by UAV as input variables of the model and using the ARD model can significantly improve the accuracy of Fv/Fm estimation at flowering stage. This approach provides new technical support for rapid and accurate monitoring of Fv/Fm in spring wheat in the Hetao Irrigation District.

Summer phytoplankton photosynthetic characteristics in the Changjiang River Estuary and the adjacent East China Sea

IntroductionThe Changjiang (Yangtze) River is one of the largest rivers in the world, and its estuary and offshore plume create a diversity of ecological habitats for the phytoplankton community. The phytoplankton community has to balance between light limitation in the sediment-laden inshore waters and nutrient limitation in the offshore waters. Active fluorescence measurements can provide rapid, non-intrusive estimates of photosynthetic characteristics at high spatial and temporal resolution.MethodsIn the summer of 2020, a field survey of hydrodynamic characteristics, availability of nutrients, the maximum quantum efficiency of photosystem II (Fv/Fm), and rapid light curves across the Changjiang River Estuary and its adjacent sea was conducted, assessing relationships between photosynthetic physiology and biomass accumulation.ResultsThe photosynthetic activities significantly differed among the turbid river water, the stratified river plume water, and the oceanic East China Sea Water. The photosynthetic physiology of phytoplankton was the most active near the front of Changjiang Diluted Water, where the Fv/Fm was over 0.5.DiscussionPhytoplankton photosynthesis was alleviated from light limitation downstream of the river mouth, and benefited from phosphorus supply via tidal mixing and upwelling. The relatively suitable light and nutrients led to high photosynthetic activities, supporting increased productivity and biomass in this water. The phytoplankton in the Changjiang estuary rivermouth were under intense stress, suggested by the Fv/Fm values under 0.3. Also, the strong vertical mixing process diluted the river nutrients before the phytoplankton consumed them. Nutrients further limited the phytoplankton offshore in the East China Sea.

Drought Tolerance Assessment of Okra (Abelmoschus esculentus [L.] Moench) Accessions Based on Leaf Gas Exchange and Chlorophyll Fluorescence

Physiological and complementary phenotypic traits are essential in the selection of drought-adapted crop genotypes. Understanding the physiological response of diverse okra genotypes under drought stress conditions is critical to the selection of drought-tolerant accessions for production or breeding. The objective of this study was to assess the levels of drought tolerance in preliminarily selected okra accessions based on leaf gas exchange and chlorophyll fluorescence to determine best-performing genotypes for drought-tolerance breeding. Twenty-six genetically diverse okra accessions were screened under non-stressed (NS) and drought-stressed (DS) conditions under a controlled glasshouse environment using a 13 × 2 alpha lattice design in three replicates, in two growing seasons. Data were subjected to statistical analyses using various procedures. A significant genotype × water condition interaction effect was recorded for transpiration rate (T), net CO2 assimilation (A), intrinsic water use efficiency (WUEi), instantaneous water use efficiency (WUEins), minimum fluorescence (Fo'), maximum fluorescence (Fm'), maximum quantum efficiency of photosystem II photochemistry (Fv'/Fm'), the effective quantum efficiency of PSII photochemistry (ɸPSII), photochemical quenching (qP), nonphotochemical quenching (qN) and relative measure of electron transport to oxygen molecules (ETR/A). The results suggested variable drought tolerance of the studied okra accessions for selection. Seven principal components (PCs) contributing to 82% of the total variation for assessed physiological traits were identified under DS conditions. Leaf gas exchange parameters, T, A and WUEi, and chlorophyll fluorescence parameters such as the ɸPSII, Fv'/Fm', qP, qN, ETR and ETR/A had high loading scores and correlated with WUEi, the ɸPSII, qP and ETR under DS conditions. The study found that optimal gas exchange and photoprotection enhance drought adaptation in the assessed okra genotypes and tested water regimes. Using the physiological variables, the study identified drought-tolerant accessions, namely LS05, LS06, LS07 and LS08 based on high A, T, Fm', Fv'/Fm' and ETR, and LS10, LS11, LS18 and LS23 based on high AES, Ci, Ci/Ca, WUEi, WUEins, ɸPSII and AES. The selected genotypes are high-yielding (≥5 g/plant) under drought stress conditions and will complement phenotypic data and guide breeding for water-limited agro-ecologies.