Photosynthesis Parameters Research Articles

Evaluation of Salinity Tolerance Threshold of Two Wheat Cultivars Via Photosynthetic Efficiency and Ion Homeostasis

The possible growth and production of wheat have been negatively influenced by salinity stress, which is a critical environmental factor. Therefore, our study aimed to determine the salinity tolerance threshold of two wheat cultivars (Amin and Barzegar) via photochemical efficiency and ion homeostasis under eight salinity levels (0.5, 2, 4, 6, 8, 10, 12, and 14 dS m−1) using a completely randomized design with three replicates. Both wheat cultivars experienced a decrease in the investigated leaf area from the 2 dS m−1 salinity level, with the shoot and root dry weight trends remaining unchanged until the 6 dS m−1 level, followed by a change in the shoot and root dry weight trends. Some significant interactions between salinity stress and cultivars were found in photosynthetic pigments and chlorophyll fluorescence parameters. Increasing salinity stress reduced the Fv/Fm, Fv/F0 and YPII in both wheat cultivars. However, a significant increase in non-photochemical quenching (NPQ) was observed as salinity intensity increased. The increase in NPQ was approximately 30% lower in Barzegar than that in Amin under severe stress. The antioxidant enzyme activity, K+ concentration, and K+/Na+ ratio in the cultivar Barzegar were remarkably higher than those in Amin; meanwhile, Amin maintained a higher Na+ concentration under salinity stress. Accordingly, photosynthesis parameters, redox, and ionic homeostasis were observed to be linked with salinity tolerance, and Amin and Barzegar were recognized as the sensitive (salt’s tolerance threshold: 3.67 dS m−1) and tolerant (salt’s tolerance threshold: 7.13 dS m−1) cultivars, respectively. Therefore, some wheat cultivars, such as Barzegar, could manage environmental stress by improving antioxidant enzyme activities, K+ concentration, and the K+/Na+ ratio to maintain a higher tolerance threshold when salinity stress is raised.

Physiological, Photosynthetic Characteristic and Transcriptome Analysis of PsnWRKY70 Transgenic Populus simonii × Populus nigra Under Salt Stress.

The PsnWRKY70 transcription factor (TF) was reported to play an important role in the salt stress response mechanism of Populus simonii × Populus nigra in our previous research, and we also produced several PsnWRKY70 overexpression (OEXs) and RNAi suppression (REXs) P. simonii × P. nigra lines. In order to further compare the photosynthetic and physiological characteristics of NT (non-transgenic line) and transgenic lines under salt stress, the dynamic phenotypic change, Na+ and K+ content in leaf and root tissues, superoxide dismutase (SOD) and peroxidase (POD) activity, malondialdehyde (MDA) content, chlorophyll content (Chl), photosynthesis parameters (net photosynthetic rate, Pn; stomatal conductance, Gs; intercellular CO2 concentration, Ci; transpiration rate, Tr), chlorophyll fluorescence parameters (electron transport rate, ETR; maximum photochemical efficiency of photosystem II (PSII), Fv/Fm; actual efficiency of PSII, ΦPSII; photochemical quenching coefficient, qP; non-photochemical quenching, NPQ; the photosynthetic light-response curves of ΦPSII and ETR) and RNA-seq of NT, OEX and REX lines were detected and analyzed. The phenotypic observation, MDA content and Chl detection results indicate that the stress damage of REXs was less severe than that of NT and OEX lines under salt stress. Photosynthesis parameter (Pn, Gs, Tr and Ci) and chlorophyll fluorescence parameter (ETR, Fv/Fm, ΦPSII qP and NPQ) detection results indicate that the REX lines exhibited much better photosynthetic adaptability than NT and OEX lines during salt stress. The photosynthetic light-response curves of ΦPSII and ETR of NT, OEX and REX lines indicate that REXs exhibited better ability to activate the photosynthetic protection mechanism and adapt to a certain degree of strong light than NT and OEX lines under salt stress. RNA-seq analysis indicates that the DEGs between OEX1 vs. NT and REX1 vs. NT in different tissues (apical bud and fifth functional leaf) were all different in category and change trend. The expression of PsnWRKY70 was significantly up-regulated in both the apical bud and fifth functional leaf of OEX1, and showed no significant change (namely maintained low expression level) in both the apical bud and fifth functional leaf of REX1, thus indicating the negative regulation role of PsnWRKY70 in P. simonii × P. nigra under salt stress. Additionally, there were a lot of stress response-related TF genes (such as bHLH, WRKY, MYB, NAM and AP2/EREBP) and photosynthesis-related genes among all the DEGs. In REX1, the expression of three Photosystem I P700 chlorophyll a apoprotein A1 genes (Potri.003G065200, Potri.013G141800 and Potri.019G028100) and a Photosystem II protein D1 gene (Potri.013G138300) were significantly up-regulated after 6 days of salt stress. In OEX1, the Heterodimeric geranylgeranyl pyrophosphate synthase small subunit gene (Potri.015G043400) and Phospho-2-dehydro-3-deoxyheptonate aldolase 1 gene (Potri.007G095700) were significantly down-regulated after 6 days of salt stress. These photosynthesis-related genes are probably regulated by PsnWRKY70 TF in response to salt stress. In conclusion, the REX lines suffered less severe salt damage and exhibited better photosynthetic adaptability than NT and OEXs under salt stress. The differences among the DEGs between OEX1 vs. NT and REX1 vs. NT in apical bud and fifth functional leaf, and the significantly differentially expressed photosynthesis-related genes are probably the key clues for discovering the photosynthesis adaptability mechanism of PsnWRKY70 transgenic P. simonii × P. nigra under salt stress.

Physiological responses of the alien macroalga Rugulopteryx okamurae (Phaeophyceae, Heterokontophyta) to changes in nutrients and temperature.

The Asian brown macroalga Rugulopteryx okamurae has invaded the oligotrophic areas of Mediterranean coasts since 2015, with drastic impacts on environmental conditions and socioeconomic activities in coastal areas in Europe. Therefore, it is intriguing how this species is able to grow and expand at the observed rates. In this context, the physiological responses of R. okamurae to changing nutrient concentrations and temperature were analyzed. Two experiments were conducted, evaluating six combinations of nitrate and phosphate concentrations and their potential interaction with temperature. Nutrient uptake efficiency (NUE) and rates (NUR), photosynthetic responses, growth rates, and biomass composition were evaluated. Photosynthesis parameters, soluble proteins, and -NUR increased with increasing N:P ratio; however, -NUR was very similar in all treatments. The species showed high capacity for nitrate assimilation, which was rapidly modulated by its external concentration and temperature (more than 90% of NO3-NUE after 5 days in treatments with N:P rations of 5, 10, 16, 25, and 40 N to 1 P). Consequently, N-nutrients were removed from the water by R. okamurae and likely stored inside the cells. This process will allow the alga to maintain high growth rates if thalli are moved to oligotrophic areas, favoring its spreading to many marine environments. Additionally, fucoxanthin was the predominant carotenoid in this species, although its content was lower than in other brown macroalgae species (mean value of 0.51 ± 0.05 mg · g-1 DW). However, since a huge amount of R. okamurae is observed recurrently on beaches, the use of this biomass might be proposed to compensate partially for its impacts.

Brassinolide Promotes the Growth of Zanthixylum schinifolium by Improving Photosynthetic Efficiency and Antioxidant Capacity

As a plant growth regulator, brassinolide (BL) is essential for enhancing plant growth and development. Studies on how BL affects the growth and development of prickly ash (Zanthixylum schinifolium) are scarce, nevertheless. Thus, the purpose of this study was to investigate how Z. schinifolium growth and development were affected by the application of BL (0, 0.1, 0.2, 0.3, 0.4, and 0.5 mg/L). According to the results, the 0.4 mg/L BL treatment had improved the plant height and leaf length after 30 days of treatment, which was displayed in an increase of 8.75% and 20.48%, respectively, when compared to the control (distilled water). On day 30, Z. schinifolium’s basal diameter, leaf breadth, compound leaf length, and leaf weight all rose noticeably after treatment with 0.4 mg/L BL. Furthermore, the 0.4 mg/L BL treatment raised the levels of osmotic substances (proline, soluble sugar, and soluble protein) and photosynthesis parameters (chlorophyll a, chlorophyll b, PSII, Fv/Fm, NPQ, and qP) in Z. schinifolium compared to the control. It also decreased the levels of malonaldehyde, increased the activities of antioxidant enzymes (POD, SOD, CAT, and APX), and increased the contents of non-enzymatic antioxidants (ASA and GSH). Accordingly, these findings implied that BL might be crucial in fostering Z. schinifolium growth and development by boosting antioxidant capacity, decreasing malonaldehyde concentration, preserving water balance, and improving photosynthesis.

Effects of ECMF Isolated from Mining Areas on Water Status, Photosynthesis Capacity, and Lead Ion Transport of Populus alba Under Pb Stress.

Native ectomycorrhizal fungi (ECMF) are generally more effective than non-native ECMF in facilitating the phytoremediation of heavy metal (HM) ions from contaminated soils. This study aimed to investigate the contributions of four ECMF species-Suillus luteus, Suillus flavidus, Suillus variegatus, and Gomphidius glutinosus-that were isolated from mining areas to the growth, water status, photosynthesis, and metallothionein gene expression of Populus alba exposed to varying concentrations of lead (Pb). The experiment lasted two months and involved P. alba cuttings subjected to Pb concentrations of 0, 200, and 400 mg kg-1, representing no Pb stress, moderate Pb stress, and severe Pb stress, respectively. Results indicated that S. flavidus significantly enhanced the growth, water status, photosynthesis parameters, and metallothionein gene expression of P. alba under Pb stress, whereas S. luteus only exhibited positive effects under severe Pb stress. S. variegatus negatively affected the growth, water status, photosynthesis, and metallothionein gene expression of P. alba under Pb stress, while no significant difference was observed between the control treatment and G. glutinosus symbiosis. Therefore, S. flavidus and S. luteus are promising ECMF species for ecological restoration in mining areas, especially in P. alba woodlands.

Smart Automatic Irrigation Enhances Sap Flow, Growth, and Water Use Efficiency in Containerized Prunus × yedoensis Matsum. Seedling.

This study conducted a comparative analysis on the effects of smart automatic and semi-automatic irrigation methods on the physiological characteristics and growth of Prunus × yedoensis Matsum. seedlings. The smart automatic irrigation system, which activates irrigation when the soil moisture drops below 15%, demonstrated superior characteristics in sap-wood area and bark ratio, as well as excellent water management efficiency, compared to the semi-automatic irrigation method, which involves watering (2.0 L) for 10 min at 60 min intervals starting at 8 AM every day. The analysis of soil moisture content changes under varying weather conditions and irrigation methods showed that smart automatic irrigation effectively maintained optimal moisture levels. Moreover, sap flow in the smart automatic irrigation treatment was more efficiently regulated in response to seasonal variations, showing a strong correlation with climatic factors such as temperature and solar radiation. In contrast, the semi-automatic irrigation treatment led to excessive sap flow during the summer due to a fixed watering schedule, resulting in unnecessary water supply. Analysis of photosynthesis parameters and chlorophyll fluorescence also revealed that smart automatic irrigation achieved higher values in light compensation and saturation points, maximizing photosynthetic efficiency. These findings suggest that the smart automatic irrigation system can enhance plant growth and water use efficiency, contributing to sustainable water management strategies. This research provides critical foundational data for developing efficient agricultural and horticultural irrigation management strategies in response to future climate change.

Drought and heat stress interactions: Unveiling the molecular and physiological responses of Persian walnut

While numerous studies explored the response of walnut plants to drought stress (DS), there remains a significant gap in the knowledge regarding the impact of heat stress (HS) and the combined effects of DS and HS on the recovery capacity of walnut trees. This study aimed to investigate the mechanism of Persian walnut (cv. Chandler) response to the combined DS and HS, focusing on various aspects including photosynthesis, water relations, and osmotic regulation. The treatments involved subjecting plants to DS (through a withholding method for 24 d), HS (gradually up to 40 °C for 8 d), and a combined DS and HS, which were compared to a control group (no stress) during the stress and recovery phases. The results showed that DS had significantly more negative effects on chlorophyll content, relative water content (RWC), leaf water potential (WP), osmotic potential (OP) compared to HS. Involvement of osmoregulation mechanism was detected more in DS and HS plants through the accumulation of proline, glycine Betaine and total soluble carbohydrates. The functionality of photosynthesis was significantly impacted by both HS and DS, respectively. While the HS accelerated the change of the abovementioned physiological processes in drought-stressed seedlings. Consistently, more pronounced damage was found in leaves under the combined stress, alongside the decrease RWC, chlorophyll content and fluorescence ratios. Based on the analysis of the linear mixed-effect model, the effects of combined stress and HS on photosynthesis parameters were detected in the early stages of stress compared to DS. Within a range of stresses, the abovementioned physiological processes of individual and combined-stressed plants recovered to levels comparable to those of the control. Our results also showed a substantial reduction in the expression of the photosynthetic genes (Fd, Cyt b6f, and PsbB) in Persian walnut saplings under abiotic stress conditions indicating significant damage to their photosynthetic apparatus. This study highlights that, under scenarios of aggravating drought occurring with heat, walnut seedlings could face a high risk of damage to physiological structures in relation to the synergistically increased hydraulic and thermal impairments.

An open-source LED lamp for use with the LI-6800 photosynthesis system.

Controlling light flux density during carbon dioxide assimilation measurements is essential in photosynthesis research. Commercial lamps are expensive and are based on monochromatic light-emitting diodes (LEDs), which deviate significantly in their spectral distribution compared to sunlight. Using LED-emitted white light with a color temperature similar to sunlight, we developed a cost-effective lamp compatible with the LI-6800 Portable Photosynthesis System. When coupled with customized software, the lamp can be controlled via the LI-6800 console by a user or Python scripts. Testing and calibration show that the lamp meets the quality needed to estimate photosynthesis parameters. The lamp can be built using a basic electronics lab and a 3D printer. Calibration instructions are supplied and only require equipment commonly available at plant science laboratories. The lamp is a cost-effective alternative to perform photosynthesis research coupled with the popular LI-6800 photosynthesis measuring system.

Critical stages in pea photosynthesis impaired by tetracycline as an environmental contaminant.

The widespread use of antibiotics in intensive animal husbandry, and the agricultural utilization of manure from such farms, imposes a significant burden on the environment. Consequently, the effects of antibiotics should be studied not only in animals and humans but also in all components of biocenoses and agrocenoses. In our study, we analyze the impact of four different concentrations of tetracycline present in soil (0, 5, 50, and 500mg/kg of soil) on the growth and key photosynthesis parameters of pea seedlings: chlorophyll concentration, aminolevulinic acid concentration, aminolevulinic acid dehydrogenase activity, and ribulose bisphosphate carboxylase-oxygenase (RuBisCO) activity. At the lowest tetracycline concentration, chlorophyll content decreased by 13% compared to the control (0 tetracycline), while at the highest antibiotic concentration, it decreased by as much as 27%. Similarly, the decrease in aminolevulinic acid (a chlorophyll precursor) concentration was significant, amounting to 34%. However, the activity of the dehydrogenase enzyme, which consumes this precursor, decreased even more drastically by 51%, indicating significant disturbances in the light phase of photosynthesis. However, the activity of RuBisCO in pea plants subjected to tetracycline was even more severely affected, dropping by 58%, 69%, and 70% in soils with increasing concentrations of tetracycline. The reduction in enzyme activity could only partially be explained by a less pronounced decrease in the quantity of RuBisCO (large subunit) protein, which amounted to 6.5%, 11%, and 35% for tetracycline concentrations of 5, 50, and 500mg/kg of soil, respectively.

Identification of autophagy gene family in potato and the role of StATG8a in salt and drought stress.

Autophagy is a highly conserved method of recycling cytoplasm components in eukaryotes. It plays an important role in plant growth and development, as well as in response to biotic and abiotic stresses. Although autophagy-related genes (ATGs) have been identified in several crop species, their particular role in potato (Solanum tuberosum L.) remains unclear. Several transcription factors and signaling genes in the transgenic lines of the model plant Arabidopsis thaliana, such as AtTSPO, AtBES1, AtPIP2;7, AtCOST1 as well as AtATI1/2, ATG8f, GFP-ATG8F-HA, AtDSK2, AtNBR1, AtHKT1 play crucial functions under drought and salt stresses, respectively. In this study, a total of 29 putative StATGs from 15 different ATG subfamilies in the potato genome were identified. Their physicochemical properties, evolutionary connections, chromosomal distribution, gene duplication, protein-protein interaction network, conserved motifs, gene structure, interspecific collinearity relationship, and cis-regulatory elements were analyzed. The results of qRT-PCR detection of StATG expression showed that 29 StATGs were differentially expressed in potato's leaves, flowers, petiole, stem, stolon, tuber, and root. StATGs were dynamically modulated by salt and drought stresses and up-regulated under salt and drought conditions. Our results showed that the StATG8a localized in the cytoplasm and the nucleus. Potato cultivar "Atlantic" overexpressing or downregulating StATG8a were constructed. Based on physiological, biochemical, and photosynthesis parameters, potato lines overexpressing StATG8a exhibited 9 times higher drought and salt tolerance compared to non-transgenic plants. In contrast, the potato plants with knockdown expression showed a downtrend in drought and salt tolerance compared to non-transgenic potato lines. These results could provide new insights into the function of StATG8a in salt and drought response and its possible mechanisms.

Elevated CO2 and Nitrogen Supply Boost N Use Efficiency and Wheat (T. aestivum cv. Yunmai) Growth and Differentiate Soil Microbial Communities Related to Ammonia Oxidization.

Elevated CO2 levels (eCO2) pose challenges to wheat (Triticum aestivum L.) growth, potentially leading to a decline in quality and productivity. This study addresses the effects of two ambient CO2 concentrations (aCO2, daytime/nighttime = 410/450 ± 30 ppm and eCO2, 550/600 ± 30 ppm) and two nitrogen (N) supplements (without N supply-N0 and with 100 mg N supply as urea per kg soil-N100) on wheat (T. aestivum cv. Yunmai) growth, N accumulation, and soil microbial communities related to ammonia oxidization. The data showed that the N supply effectively mitigated the negative impacts of eCO2 on wheat growth by reducing intercellular CO2 concentrations while enhancing photosynthesis parameters. Notably, the N supply significantly increased N concentrations in wheat tissues and biomass production, thereby boosting N accumulation in seeds, shoots, and roots. eCO2 increased the agronomic efficiency of applied N (AEN) and the physiological efficiency of applied N (PEN) under N supply. Plant tissue N concentrations and accumulations are positively related to plant biomass production and soil NO3--N. Additionally, the N supply increased the richness and evenness of the soil microbial community, particularly Nitrososphaeraceae, Nitrosospira, and Nitrosomonas, which responded differently to N availability under both aCO2 and eCO2. These results underscore the importance and complexity of optimizing N supply and eCO2 for enhancing crop tissue N accumulation and yield production as well as activating nitrification-related microbial activities for soil inorganic N availability under future global environment change scenarios.

Molybdenum Disulfide Nanoparticle Enhancing Photosynthesis in Solanum Lycopersicum

AbstractPhotosynthesis is a dynamic, complex, photo‐catalytic process that plays a key role in the growth and development of plants. It converts solar energy to chemical energy by precise organisation of light harvesting molecules in the photosynthetic system. Artificially imitating such systems is difficult due to the complexity of different cascades associated with photosynthesis. Nanoparticle mediated photocatalytic complexes have been shown to improve photosynthesis efficiency. Nanomaterials, such as molybdenum disulfide (MoS2) efficiently capture sunlight and assist in photosynthesis enhancement and nanosheets offer an additional advantage of increased surface area for sunlight harnessing. Foliar nutrition supplementation provides high yield potential to crops and their application in small doses improves the photosynthesis and elevates the plant performance. This study aims at mapping the efficiency of facile one‐pot hydrothermally synthesized MoS2 nanosheets in enhancing the photosynthetic ability of tomato plants. The treatments included the supplementation and absence of molybdenum source to plants. Physiological features (root length, shoot length, biomass), biochemical parameters (antioxidant activity), photosynthesis parameters (carbon assimilation, stomatal conductance, transpiration rate, water use efficiency, chlorophyll and carotenoid content), uptake and translocation of MoS2 nanosheets were evaluated. Increases of 22.07 %, 49.95 % and 18.56 % in net photosynthetic rate, water use efficiency and chlorophyll content respectively, were observed in MoS2_Nano treated plants compared with untreated plants. These nanosheets improved plant photosynthesis parameters and enhanced photosystem efficiency without inducing phytotoxicity. This study demonstrates the promise of such approaches towards enhanced plant photosystem efficiency, leading to improved agricultural productivity, particularly in the regions with less sunlight.

Two Carya Species, Carya hunanensis and Carya illinoinensis, Used as Rootstocks Point to Improvements in the Heat Resistance of Carya cathayensis.

Grafting as a crucial horticultural technique has been widely used in the cultivation of Carya cathayensis (Chinese hickory), which is a unique and important economic tree in the northeast of Zhejiang Province and the south of Anhui Province. However, the existing literature lacks research on the potential impact of various rootstocks on the thermal tolerance of Chinese hickory. The objectives of this study were to evaluate heat tolerance in four distinct groups of Chinese hickory, including C. cathayensis grafted onto Carya hunanensis and Carya illinoinensis, one self-grafted group (C. cathayensis grafted onto C. cathayensis), and one non-grafted group (C. cathayensis). We examined photosynthesis parameters, phytohormones, and differentially expressed genes in the four various hickory groups subjected to 25 °C, 35 °C, and 40 °C heat stress (HS). The results demonstrated that grafting onto C. hunanensis and C. illinoinensis exhibited a higher net photosynthetic rate and stomatal conductance, lower intercellular CO2 concentration, and smaller changes in plant hormone content compared to self-grafted and non-grafted group under HS. The transcriptome results revealed that the majority of differentially expressed genes (DEGs) associated with photosynthetic pathways exhibited downregulation under HS, while the degree of variation in grafted groups using C. hunanensis and C. illinoinensis as rootstocks was comparatively lower than that observed in self-grafted and non-grafted groups. The alteration in the expression patterns of DEGs involved in plant hormone synthesis and metabolism under HS corresponded to changes in plant hormone contents. Overall, Chinese hickory grafted onto C. hunanensis and C. illinoinensis exhibited enhanced resistance to high-temperature stress at the juvenile stage.

Changes in Some Photosynthesis Indicators Under Different Donor-Acceptor Relations of Wheat Under the Influence of Drought

The results of studies of changes in some parameters of photosynthesis - the formation of leaf surface and the area of ​​other assimilating organs, the accumulation of dry above-ground biomass, chlorophyll content in the ontogenesis of wheat genotypes at different donor-acceptor relationships are presented. In the studied varieties, the dynamics of leaf surface area and the amount of increase in dry biomass during ontogenesis depend not only on the developmental phase and genotypic characteristics of the plants, but also on the state of donor-acceptor relationships in the whole plant system, as well as on the influence of drought. In all studied varieties, when half the ear was removed under both conditions, an increase in the area and dry biomass of stems and leaves was observed. With a decrease in the attracting ability of the ear, it needs significantly less leaf photosynthesis products and the remainder of the assimilates is spent on increasing the area of ​​the leaves themselves. At the same time, changes in donor-acceptor relationships affect the chlorophyll content in leaves. In all cases, the removal of leaves of the 7th tier leads to an increase in the chlorophyll content in the leaves of the 8th tier and vice versa. When half of the ear is removed, the chlorophyll content of both leaves of the 7th and 8th tiers decreases significantly.

How does silicon alleviate Cd-induced phytotoxicity in barley, Hordeum vulgare L.?

Toxic heavy metal accumulation in edible plants has become a problem worth worrying about for human health. Cadmium is one of the most toxic metals presenting high bioavailability in the environment. The main route of transfer of Cd to humans is the consumption of contaminated food which suggests that reducing of Cd absorption by plants could reduce this risk. In this context, it was suggested that silicon supply would be able to limit the transfer of Cd to the plants. Thus, this work evaluated the effects of 0.5 mM Si on Cd absorption and accumulation in barley (Hordeum vulgare L.). Plants were grown hydroponically for 21 days in the presence of 0 and 15 μM Cd2+ combined or not with 0.5 mM Si. Analyses were related to growth and photosynthesis parameters, Cd accumulation in organs and Cd subcellular distribution in the shoots. Results showed that, under Cd alone, plants showed severe toxicity symptoms as chlorosis and necrosis and produced significantly less biomass as compared to control. 0.5 mM Si in the medium culture significantly reduced Cd-induced toxicity by mitigating symptoms and restoring growth, photosynthesis, and nutrition. Si also induced a significant reduction of Cd concentration in plants and changed its sub-cellular compartmentalization by enhancing fixation to cell walls and reducing the Cd concentration in the cytoplasmic and organelles fractions. These data suggest that the application of Si could significantly increase Cd tolerance and reduce the risk of the Cd accumulation in edible plants.

Improvement of Physiological Features and Essential Oil Content of Thymus vulgaris after Soil Amendment with Chitosan Nanoparticles under Chromium Toxicity

An excessive amount of chromium in soil has detrimental effects on plant processes, and impairs food security, and public health. The application of nanoparticles may be a suitable solution and an innovative strategy by which to reduce plant abiotic stresses and pollution in the agricultural ecosystems. This research focuses on the effects of chitosan nanoparticles (CS-NPs) on thyme (Thymus vulgaris L.) plants grown in Cr-contaminated soil. The effects of CS-NPs as a soil amendment at four concentrations were investigated on plant nutrient uptake, photosynthesis parameters, antioxidant system, and essential oil (EO) content under soil Cr stress. The results show that chromium stress reduced fresh and dry weight of shoots, the uptake of macro-, and micro-elements, chlorophyll and carotenoids. The application of CS-NPs improved the antioxidant enzyme activity, reduced malondialdehyde, and increased the content of nutrients, EOs, photosynthetic pigments, and chlorophyll fluorescence parameters. The intermediate dose of chitosan nanoparticles (0.1% w/v) best valorized the content and yield of thyme EOs under chromium stress. These results are indicative that the application of CS-NPs can represent a supportive approach for plant production in soils contaminated with heavy metals.

Influence of Time-Lag Effects between Winter-Wheat Canopy Temperature and Atmospheric Temperature on the Accuracy of CWSI Inversion of Photosynthetic Parameters.

When calculating the CWSI, previous researchers usually used canopy temperature and atmospheric temperature at the same time. However, it takes some time for the canopy temperature (Tc) to respond to atmospheric temperature (Ta), suggesting the time-lag effects between Ta and Tc. In order to investigate time-lag effects between Ta and Tc on the accuracy of the CWSI inversion of photosynthetic parameters in winter wheat, we conducted an experiment. In this study, four moisture treatments were set up: T1 (95% of field water holding capacity), T2 (80% of field water holding capacity), T3 (65% of field water holding capacity), and T4 (50% of field water holding capacity). We quantified the time-lag parameter in winter wheat using time-lag peak-seeking, time-lag cross-correlation, time-lag mutual information, and gray time-lag correlation analysis. Based on the time-lag parameter, we modified the CWSI theoretical and empirical models and assessed the impact of time-lag effects on the accuracy of the CWSI inversion of photosynthesis parameters. Finally, we applied several machine learning algorithms to predict the daily variation in the CWSI after time-lag correction. The results show that: (1) The time-lag parameter calculated using time-lag peak-seeking, time-lag cross-correlation, time-lag mutual information, and gray time-lag correlation analysis are 44-70, 32-44, 42-58, and 76-97 min, respectively. (2) The CWSI empirical model corrected by the time-lag mutual information method has the highest correlation with photosynthetic parameters. (3) GA-SVM has the highest prediction accuracy for the CWSI empirical model corrected by the time-lag mutual information method. Considering time lag effects between Ta and Tc effectively enhanced the correlation between CWSI and photosynthetic parameters, which can provide theoretical support for thermal infrared remote sensing to diagnose crop water stress conditions.

Effects of nutrient conditions to stem photosynthesis and growth in Ephedra intermedia (Ephedraceae)

ABSTRACT Ephedra intermedia Schrenk et C.A.Meyer (Ephedraceae, Gnetales, Gymnospermae) contains ephedrine and pseudoephedrine, and has been used as Ephedra herb, a traditional medicine. Instead of degenerated leaves, photosynthetic assimilation is performed in their stems. Recently domestic cultivation of this species has been required, but relevant nutrient conditions for cultivation remain uncertain. In this study, we examined stem photosynthetic parameters in E. intermedia plants grown under different nutrient conditions in order to clarify relationships between the photosynthetic parameters and growth in their stems. Also, we examined whether the regulation of two photosystems of the photosynthetic electron transport system in E. intermedia stems is similar to that of angiosperm leaves. We cultivated E. intermedia plants under various nutrient conditions with different levels of nitrogen (N), and regularly measured CO2 assimilation rates, parameters of the photosynthetic electron transport system, and growth of E. intermedia stems. The stem growth was better under the condition with the additional ordinary chemical fertilizer compared to those with urea or magnesium lime. The seasonal changes were observed in the CO2 assimilation rates, Y(II), the quantum yield of photosystem II (PSII), and Y(ND), the non-photochemical yield due to donor side limitations in photosystem I (PSI). However, these parameters differed between nutrient conditions to small extents, and were not related to stem growth. Therefore, the measured parameters of photosynthesis could not explain the difference in stem growth between nutrient conditions. Although the photosynthetic parameters seasonally changed, the tight relationships between Y(ND), the PSI parameter, and Y(II) or Y(NPQ), the PSII parameters, were found throughout the seasons. These relationships between two photosystems in stems of gymnosperm E. intermedia were as the same as those in angiosperm leaves, although a flavodiiron protein can function as the electron sink in the stems of E. intermedia. This balance between two photosystems may be regulated by the system dependent on the thylakoid lumen pH, which may lead to the protection of two photosystems throughout the seasons.

Exploring natural genetic variation in photosynthesis-related traits of barley in the field.

Optimizing photosynthesis is considered an important strategy for improving crop yields to ensure food security. To evaluate the potential of using photosynthesis-related parameters in crop breeding programs, we measured chlorophyll fluorescence along with growth-related and morphological traits of 23 barley inbred lines across different developmental stages in field conditions. The photosynthesis-related parameters were highly variable, changing with light intensity and developmental progression of plants. Yet, the variation in photosystem II quantum yield observed among the inbred lines in the field largely reflected the variation in CO2 assimilation properties in controlled climate chamber conditions, confirming that the chlorophyll fluorescence-based technique can provide proxy parameters of photosynthesis to explore genetic variation under field conditions. Heritability (H2) of the photosynthesis-related parameters in the field ranged from 0.16 for the quantum yield of non-photochemical quenching to 0.78 for the fraction of open photosystem II center. Two parameters, the maximum photosystem II efficiency in the light-adapted state (H2=0.58) and the total non-photochemical quenching (H2=0.53), showed significant positive and negative correlations, respectively, with yield-related traits (dry weight per plant and net straw weight) in the barley inbred lines. These results indicate the possibility of improving crop yield through optimizing photosynthetic light use efficiency by conventional breeding programs.

Rhizophagus irregularis and biochar can synergistically improve the physiological characteristics of saline-alkali resistance of switchgrass.

Inoculation of arbuscular mycorrhizal fungi (AMF) or biochar (BC) application can improve photosynthesis and promote plant growth under saline-alkali stress. However, little is known about the effects of the two combined on growth and physiological characteristics of switchgrass under saline-alkali stress. This study examined the effects of four treatments: (1) no AMF inoculation and no biochar addition (control), (2) biochar (BC) alone, (3) AMF (Rhizophagus irregularis, Ri) alone, and (4) the combination of both (BC+Ri) on the plant biomass, antioxidant enzymes, chlorophyll, and photosynthetic parameters of switchgrass under saline-alkali stress. The results showed that the above-ground, belowground and total biomass of switchgrass in the BC+Ri treatment group was significantly higher (+136.7%, 120.2% and 132.4%, respectively) than in other treatments compared with Control. BC+Ri treatment significantly increased plant leaves' relative chlorophyll content, antioxidant enzyme activity, and photosynthesis parameters. It is worth noting that the transpiration rate, stomatal conductance, net photosynthetic rate, PSII efficiency and other photosynthetic-related indexes of the BC+Ri treatment group were the highest (38% to 54% higher than other treatments). The fitting results of light response and CO2 response curves showed that the light saturation point, light compensation point, maximum carboxylation rate and maximum electron transfer rate of switchgrass in the Ri+BC treatment group were the highest. In conclusion, biochar combined with Ri has potential beneficial effects on promoting switchgrass growth under saline-alkali stress and improving the activity of antioxidant enzymes and photosynthetic characteristics of plants.