Sub-stomatal CO2 Concentration Research Articles

Foliar application of phosphoric acid mitigates oxidative stress induced by herbicides in soybean, maize, and cotton crops

Foliar fertilization presents a potential solution in alleviating oxidative stress triggered by herbicide exposure. Enhancing our comprehension of the interplay between foliar fertilization, oxidative stress, and herbicide application is pivotal for enhancing crop yield. Carfentrazone, a herbicide, prompts the buildup of reactive oxygen species, leading to detrimental effects on cell membranes and the manifestation of chlorotic spots on leaves. This research administered carfentrazone-ethyl to soybean, maize, and cotton to induce stress. The herbicide application was followed by foliar application of phosphorus (H3PO4) to evaluate its effect on phytotoxicity recovery. The evaluations included leaf nutritional analyses, gas exchange measurements (photosynthesis, stomatal conductance, substomatal CO2 concentration, and Leaf transpiration), photosynthetic pigments (chlorophylls and carotenoids), oxidative stress indicators (MDA, H2O2, SOD, CAT and APX), and productivity parameters (height, number of branches, pods, grains, 100-grain weight, and yield), in addition to the activity of the enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which is crucial for carbon fixation and the photosynthetic efficiency of plants. Phosphorus (P) improved chlorophyll levels by up to 28.8% and Rubisco activity by up to 24.8%, leading to increases in the net photosynthetic rate by up to 40.2%, stomatal conductance, water use efficiency, and carboxylation. In addition, foliar P fertilization enhanced antioxidant metabolism, with reductions in markers of oxidative stress (H2O2 and MDA) by up to 39.1%. Collectively, these effects of foliar P fertilization increased the productivity of the three crops by up to 55.9%, indicating that foliar supplementation with P is an effective strategy to mitigate phytotoxicity symptoms.. In soybeans at the V4 and V6 stages, it has been shown to improve net photosynthesis, enhance Rubisco activity, and reduce oxidative stress. In maize, the V4 stage proved to be more effective, increasing Rubisco activity and improving productivity. For cotton, the B1 stage was more beneficial, resulting in increased boll weight and fiber yield. This study introduces an innovative approach of foliar P-supplementation to mitigate herbicide-induced oxidative stress in crops. This management strategy enhances crop resilience, improves yield stability, and provides a sustainable solution to a critical challenge in modern agriculture.

Influence of N-Acetylglucosamine and Melatonin Interaction in Modeling the Photosynthetic Component and Metabolomics of Cucumber under Salinity Stress.

The application of N-acetylglucosamine (GlcNAc) and melatonin (Mel) in agriculture could be a promising avenue for improving crop resilience and productivity, especially under challenging environmental conditions. In the current study, we treated the cucumber plant with GlcNAc and Mel solely and combinedly under salt stress (150 mM) then studied photosynthetic attributes using the transient OJIP fluorescence method. The results showed that the combination of GlcNAc × Mel significantly improved the plant morphological attributes, such as root and shoot biomass, and also improved chlorophyll and photosynthetic components. The mineral elements such as K, Mg, Ca, and P were significantly elevated, whereas a lower influx of Na was observed in GlcNAc × Mel treated cucumber shoots. A significant reduction in abscisic acid was observed, which was validated by the reduction in proline content and the increase in stomatal conductance (Gs), transpiration rate (E), and substomatal CO2 concentration (Ci). Furthermore, the activities of antioxidants such as polyphenol and flavonoid were considerably improved, resulting in a decrease in SOD and CAT with GlcNAc × Mel treatment. In addition, GlcNAc × Mel treatment dropped levels of the toxic radical Malondialdehyde (MDA) and elevated amino acids in cucumber shoots. These findings suggest that the combination of GlcNAc × Mel could be an effective elicitor for modeling plant metabolism to confer stress tolerance in crops.

Basal ABA signaling balances transpiration and photosynthesis.

The balance between the CO2 entry for photosynthesis and transpiration water loss is crucial for plant growth, and ABA signaling can affect this equilibrium. To test how ABA balances plant growth and environmental adaptation, we performed molecular genetics studies in the biotech crop Nicotiana benthamiana under well-watered or drought conditions. Studies on ABA signaling in crops are complicated by the multigenic nature of the PYR/PYL/RCAR ABA receptor family and its functional redundancy, which is particularly challenging in polyploid plants. We have generated a pentuple pyl mutant in the allotetraploid Nicotiana benthamiana through CRISPR/Cas9 gene editing. The pentuple mutant is impaired in 2 NbPYL1-like and 3 NbPYL8-like receptors, affecting the regulation of transpiration and several ABA-dependent transcriptional processes. RNA-seq and metabolite analysis revealed that the synthesis of galactinol, an essential precursor for the osmoprotective raffinose family of oligosaccharides, is ABA-dependent and impaired in the mutant under osmotic stress. In contrast, our results show that, under well-watered conditions, partial inactivation of ABA signaling leads to higher CO2 entry and photosynthesis in the mutant than in WT. Photosynthesis analyses revealed an increased CO2 diffusion capacity mediated by higher stomatal and mesophyll conductances, and higher substomatal CO2 concentration in the pentuple mutant. RNA-seq analyses revealed that genes associated with cell wall loosening (e.g., expansins) and porosity were strongly downregulated by ABA in WT. In summary, a partial relief of the ABA control on transpiration mediated by ABA receptors positively affects photosynthesis when water is not limited, at the expense of reduced water use efficiency.

Physiological, metabolic and hormonal responses of two Pinus spp. with contrasting susceptibility to brown-spot needle blight disease.

Needle blights are serious fungal diseases affecting European natural and planted pine forests. Brown-spot needle blight (BSNB) disease, caused by the fungus Lecanosticta acicola, causes canopy defoliation and severe productivity losses, with consequences depending on host susceptibility. To gain new insights into BSNB plant-pathogen interactions, constitutive and pathogen-induced traits were assessed in two host species with differential disease susceptibility. Six-month-old Pinus radiata D. Don (susceptible) and Pinus pinea L. (more resistant) seedlings were needle inoculated with L. acicola under controlled conditions. Eighty days after inoculation, healthy-looking needles from symptomatic plants were assessed for physiological parameters and sampled for biochemical analysis. Disease progression, plant growth, leaf gas-exchanges and biochemical parameters were complemented with hormonal and untargeted primary metabolism analysis and integrated for a holistic analysis. Constitutive differences between pine species were observed. Pinus pinea presented higher stomatal conductance and transpiration rate and higher amino and organic acids, abscisic acid as well as putrescine content than P. radiata. Symptoms from BSNB disease were observed in 54.54% of P. radiata and 45.45% of P. pinea seedlings, being more pronounced and generalized in P. radiata. For both species, plant height, sub-stomatal CO2 concentration and water-use efficiency were impacted by infection. In P. radiata, total soluble sugars, starch and total flavonoids content increased after infection. No differences in hormone content after infection were observed. However, secondary metabolism was induced in P. pinea visible through total phenolics, flavonoids and putrescine accumulation. Overall, the observed results suggest that P. pinea constitutive and induced traits may function as two layers of a defence strategy which contributed to an increased BSNB resistance in comparison with P. radiata. This is the first integrative study linking plant physiological and molecular traits in Pinus-Lecanosticta acicola pathosystem, contributing to a better understanding of the underlying resistance mechanisms to BSNB disease in pines.

Efluente da piscicultura e tempos de recirculação nas trocas gasosas e nutrição do agrião hidropônico

ABSTRACT The present study evaluated the potential use of fish farming effluent incorporated into the standard nutrient solution and recirculation time on gas exchange and macro and micronutrient contents of watercress in a hydroponic system. The study was conducted in randomized blocks, in a split-plot scheme with 4 replicates, in two experiments carried out in spring and summer seasons. Plots were composed of different proportions of nutrient solution (NS) and fish farming effluent (FFE): S1 (0% NS and 100% FFE), S2 (25% NS and 75% FFE), S3 (50% NS and 50% FFE), S4 (75% NS and 25% FFE), and S5 (100% NS and 0% FFE). Subplots consisted of two solution recirculation times (Time 1 – T1: 15 for 15 min and Time 2 – T2: 15 for 30 min), totaling 40 experimental plots. Net photosynthesis, stomatal conductance, transpiration, substomatal CO2 concentration, SPAD index, and macro and micronutrient contents were evaluated. Net photosynthesis showed a quadratic fit in both cultivation cycles, with maximum values observed with use of 86.0% NS (spring) and 64.9% NS (summer). Leaf N and P contents indicate that the use of approximately 70% NS can be considered satisfactory, as it promoted the highest values of these macronutrients. Using fish farming effluent can enable the production of watercress in hydroponic systems, influencing the nutritional status of the crop.

Photosynthesis governed by nanoparticulate titanium dioxide. The Pisum sativum L. case study

Wide availability of anthropogenic TiO2 nanoparticles facilitates their penetration into environment and prompts interactions with plants. They alter plants growth and change their nutritional status. In particular, metabolic processes are affected. In this work the effect of nanometric TiO2 on photosynthesis efficiency in green pea (Pisum sativum L.) was studied. Hydroponic cultivations with three Ti levels (10; 50 and 100 mg L−1) were applied. At all concentrations nanoparticles penetrated into plant tissues and were detected by the single particle ICP-MS/MS method. Nanoparticles altered the CO2 assimilation rate and gas exchange parameters (i.e. transpiration, stomatal conductance, sub-stomatal CO2 concentration). The most pronounced effects were observed for Ti 50 mg L−1 cultivation where photosynthesis efficiency, transpiration and stomatal conductance were increased by 14.69%, 4.58% and 8.92%, respectively. They were further confirmed by high maximum ribulose 1,5-bisphosphate carboxylation rate (27.40% increase), maximum electron transport rate (21.51% increase) and the lowest CO2 compensation point (45.19% decrease). Furthermore, concentrations of Cu, Mn, Zn, Fe, Mg, Ca, K and P were examined with the most pronounced changes observed for elements directly involved in photosynthesis (Cu, Zn, Mn, and Fe). The Cu concentrations in roots, stems and leaves for Ti 50 mg L−1 cultivation were below the control by 33.15%, 38.28% and 10.76%, respectively. The Zn content in analogous treatment and organs decreased by 30.24%, 26.69% and 13.35%. The Mn and Fe levels in leaves were increased by 72.22% and 50.32%, respectively. Our results indicated that plant defence mechanisms which restrain the water uptake have been overcome in pea by photocatalytic activity of nanoparticulate TiO2 which stimulated photosynthesis. On the contrary to the substantial stomatal conductance, the transpiration has been reduced because exceptional part of water flow was already consumed in chloroplasts and could not have been freed to the atmosphere.

Spatial relationships between the van Genuchten soil-water retention curve parameters and photosynthetic gas exchange variables in a wheat field

Photosynthetic gas exchange indices can be used to assess spatial variation of crop growth and yield on the field. Spatial variation of soil parameters can be an important tool to assess and manage crop growth status and product quality in the field, given the impact of soil on photosynthetic function. The purpose of this study was to evaluate the spatial relationships between the van Genuchten (vG) soil water retention curve parameters, soil properties and the photosynthetic gas exchange indices in a wheat field with an extension of 200 ha. Different variables of soil and plant were determined at the 100 nodes of a nearly regular grid (150 m × 150 m) over the whole field. The range of variograms showed high variability for photosynthetic parameters and vG parameters, and greater continuity for soil parameters. Photosynthesis was significantly correlated with saturated soil water content (θs) (r = 0.26*), θ1500kPa (permanent wilting point) (0.21*), porosity (r = 0.31**), bulk density (r = −0.32**) and clay content (r = 0.24*). Cross correlogram and linear model of coregionalization of sub-stomatal CO2 concentration (Ci) and stomatal conductance (gs) with photosynthetic rate (A) and transpiration (E) showed opposite relation with soil and hydraulic properties. Regressing of maps showed that a large part of the total variation in A (66%), Ci (79%) and gs (37%) was explained by soil variables. Also, from the visual inspection of the interpolated maps the field can be divided in zones characterized by different soil properties and these maps could be effectively used by farmers to improve wheat yield. On the other hand, results of this study may enhance understanding of the soil properties and soil hydraulic parameters effects on gas exchange parameters of the plant and delineation of the field in homogeneous zones that could be advantageously used by farmers to make informed decisions in site-specific management.

Application of candidate endophytic fungi isolated from extreme desert adapted trees to mitigate the adverse effects of drought stress on maize (Zea mays L.)

The survival of plants under adverse conditions in desert habitats is related to microbial interactions, which can be an innovative strategy for reducing the effects of drought stress in colonized plants. In this study, two endophytic fungi, Trichoderma harzianum, and Fusarium solani, were recovered from the roots of trees in desert regions of Iran. A greenhouse experiment with two fungal agents (control, T. harzianum, F. solani, and T. harzianum + F. solani) and drought (100, 75, and 50% water-holding capacity) was performed on maize (Zea mays L.). Findings indicate that increasing drought levels negatively affect maize plant growth and physiological traits. However, the symbiotic relationship between fungal endophytes and maize roots increased fresh and dry biomass, root/shoot ratio, leaf area, relative water content, and membrane stability index compared with their control counterparts. Maize plants inoculated with endophytic fungi had 52.07, 40, 33.03, and 55.62% higher total phenolic, proline and soluble sugar concentrations, respectively than uninoculated controls. Photosynthetic parameters, including chlorophyll and carotenoid pigments, chlorophyll fluorescence, and gas exchange, were improved in the endophyte-treated plants. However, with increasing drought stress, maize plants colonized with endophytes, electrolyte leakage, and sub-stomatal CO2 concentrations decreased by 28.93% and 47.62%, respectively, compared to endophyte-free plants. When plants were exposed to higher levels of drought stress, endophytes were more effective in improving most parameters, and inoculation of maize seedlings with a combination of endophytes isolated from plants in harsh regions was more effective in increasing their tolerance to drought stress than individual inoculation of each fungus.

The Photosynthesis of Populus euphratica Oliv. Is Not Limited by Drought Stress in the Hyper-Arid Zone of Northwest China

The Ejin Oasis is located in the lower reaches of the Heihe River Basin of northwestern China. It is one of the most arid regions in the world, and Populus euphratica Oliv. is the foundation species of the desert riparian forests there. The photosynthesis of P. euphratica is one of the first physiological processes that is most likely to be affected by the extremely arid climate conditions. The factors impacting photosynthesis can be divided into stomatal and non-stomatal limitations. In order to investigate whether the photosynthesis of P. euphratica was limited and, if so, whether this limitation was caused by drought stress in the P. euphratica Forest Reserve on the Ejin River, we analyzed stomatal, non-stomatal, and relative stomatal limitations (reflecting the relative importance of the stoma in controlling the processes of photosynthesis) of photosynthesis. The results show that, at the beginning of the midday depression of photosynthesis, the values of stomatal limitation of photosynthesis (Ls) peaked, with its predominance being supported by sub-stomatal CO2 concentrations (Ci) being at a minimum. Thereafter, Ls decreased and non-stomatal limitation (Ci/stomatal conductance (gs)) increased sharply, indicating that the non-stomatal limitation of photosynthesis was predominant. Both Ls and relative stomatal limitation of photosynthesis increased in the morning, and then decreased, whereas Ci/gs showed the opposite trend. We concluded that P. euphratica did not experience drought stress by analyzing leaf water potential, groundwater table, and the decoupling coefficient (a parameter characterizing the coupling degree between vegetation canopy and atmospheric water vapor flux); however, the Ls values of P. euphratica were much greater than those of other species. This was likely because P. euphratica has a relatively conservative water use strategy even when growing under favorable water conditions. Extremely high temperatures caused the closure of the stoma to reduce transpiration, resulting in more intense stomatal limitations of photosynthesis.

Variability of photosynthetic and related traits in maize and other summer crops in a temperate humid area

Photosynthetic rate and water use efficiency (WUE) are crucial for the sustainable use of water in agriculture. Our objective was to analyze the variability of photosynthetic and related traits in maize (Zea mays L.) and other summer crops in a temperate humid area. We evaluated photosynthetic parameters in maize for three years and compared them to pigeonpea and chickpea, adapted to arid environments, and pepper, tomato and common bean, as irrigated crops. Variability was significant in maize for most photosynthetic parameters and no consistent patterns of variability were found among genotypes. Compared to other crops, maize (C4 crop) had the highest CO2 assimilation and WUE, and the lowest stomatal conductance, substomatal CO2 concentration, and transpiration. CO2 assimilation was lowest for chickpea, stomatal conductance was highest for pigeonpea, substomatal CO2 concentration was highest for tomato and pigeonpea, transpiration was highest for pigeonpea, and WUE was lowest for pigeonpea. Chickpea lacked variability for photosynthetic traits, while pigeonpea has the largest potential for improving photosynthetic traits. Net assimilation, conductance, and transpiration could be improved in common bean, and substomatal CO2 concentration in pepper. Water Use Efficiency could be improved in some C3 crops, but more genetic biodiversity has to be identified in maize.

Proline-Induced Modifications in Morpho-Physiological, Biochemical and Yield Attributes of Pea (Pisum sativum L.) Cultivars under Salt Stress

Climate change is aggravating soil salinity, causing huge crop losses around the globe. Multiple physiological and biochemical pathways determine the ability of plants to tolerate salt stress. A pot experiment was performed to understand the impact of proline levels, i.e., 0, 10, 20 mM on growth, biochemical and yield attributes of two pea (Pisum sativum L.) cultivars (cv. L-888 and cv. Round) under salt stress (150 mM) along with control (0 mM; no stress). The pots were filled with river-washed sand; all the plants were irrigated with full-strength Hoagland’s nutrient solution and grown for two weeks before application of salt stress. Foliar spray of proline was applied to 46-day-old pea plants, once a week till harvest. Data for various growth and physio-biochemical attributes were collected from 70-day-old pea plants. Imposition of salt stress significantly checked growth, gas exchange characteristics [net CO2 assimilation rate (A), transpiration rate (E), stomatal conductance (gs)], total soluble proteins, concentration of superoxide dismutase (SOD), shoot and root K+ and Ca2+ contents, while sub-stomatal CO2 concentration (Ci), coefficient of non-photochemical quenching (qN), non-photochemical quenching (NPQ), concentration of catalase (CAT) and peroxidase (POD), free proline, and shoot and root Na+ contents increased substantially. Foliar application of proline significantly improved growth, yield, A, gs, activity of POD, and shoot and root K+ and Ca2+ contents, while decreased NPQ values in both pea cultivars under stress and non-stress conditions. Moreover, both pea cultivars showed significant differences as cv. Round exhibited a higher rate of growth, yield, gas exchange, soluble proteins, CAT activity, free proline, shoot and root K+ and Ca2+ contents compared to L-888. Hence, the outcomes of this study pave the way toward the usage of proline at 20 mM, and cv. Round may be recommended for saline soil cultivation.

Biochemical Insights into the Ability of Lemna minor L. Extract to Counteract Copper Toxicity in Maize.

Metal trace elements (MTE) can damage crops if present in excessive amounts in the environment. This research investigated the effect of a plant extract of an aquatic species, Lemna minor L. (duckweed) (LE), on the ability of maize to cope with copper (Cu) toxicity. LE reversed the effects of Cu2+ on photosynthetic activity (Pn), evapotranspiration (E), stomatal conductance (gs), sub-stomatal CO2 concentration (Ci) and biomass which did not differ from the untreated controls. LE did not regulate the amount of copper in maize leaves, but compared to Cu-treated samples, the extract decreased the hydrogen peroxide (H2O2; −26% on average) and malondialdehyde (MDA; −47% on average) content, regardless of the dosage applied. Furthermore, the activity of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) was significantly increased by LE compared to samples treated with Cu alone. Untargeted metabolomic profiling revealed that LE activated maize secondary metabolism, eliciting the content of non-enzymatic antioxidants (flavonoids, glutathione and glutathione-related compounds, tocopherols and tocotrienols) and modulating plant stress-related hormones (brassinosteroids and ABA derivatives). The results of this study are promising and pave the way for using duckweed as a biostimulant to trigger beneficial effects in maize and increase its resistance to MTEs.

Physiological and transcriptome analyses reveal the photosynthetic response to drought stress in drought-sensitive (Fengjiao) and drought-tolerant (Hanjiao) Zanthoxylum bungeanum cultivars.

As an important economical plant, Zanthoxylum bungeanum is widely cultivated in arid and semi-arid areas. The studies associated with photosynthesis under drought stress were widely carried out, but not yet in Z. bungeanum. Here, the photosynthesis of two Z. bungeanum cultivars (FJ, Z. bungeanum cv. “Fengjiao”; HJ, Z. bungeanum cv. “Hanjiao”) was analyzed under drought stress using physiological indicators and transcriptome data. Drought decreased stomatal aperture and stomatal conductance (Gsw), reduced transpiration rate (E) and sub-stomatal CO2 concentration (Ci), and lowered chlorophyll and carotenoid content, which reduced the net photosynthetic rate (Pn) of Z. bungeanum. The higher photosynthetic rate in HJ stemmed from its higher chlorophyll content, larger stomatal aperture and Gsw, and higher Ci. Weighted gene co-expression network analysis (WGCNA) identified several ABA signal transduction genes (PYL4, PYL9, and PYR1), LCH-encoding genes (LHCB4.3), and chlorophyll metabolism genes (CRD1, PORA, and CHLH). Additionally, seven transcription factor genes were identified as important factors regulating photosynthesis under drought conditions. In general, a photosynthetic response model under drought stress was built firstly in Z. bungeanum, and the key genes involved in photosynthesis under drought stress were identified. Therefore, the results in our research provide important information for photosynthesis under drought and provided key clues for future molecular breeding in Z. bungeanum.

Effect of Pyroligneous Acid on the Productivity and Nutritional Quality of Greenhouse Tomato.

Pyroligneous acid (PA) is a reddish-brown liquid obtained through the condensation of smoke formed during biochar production. PA contains bioactive compounds that can be utilized in agriculture to improve plant productivity and quality of edible parts. In this study, we investigated the biostimulatory effect of varying concentrations of PA (i.e., 0%, 0.25%, 0.5%, 1%, and 2% PA/ddH2O (v/v)) application on tomato (Solanum lycopersicum ‘Scotia’) plant growth and fruit quality under greenhouse conditions. Plants treated with 0.25% PA exhibited a significantly (p < 0.001) higher sub-stomatal CO2 concentration and a comparable leaf transpiration rate and stomatal conductance. The total number of fruits was significantly (p < 0.005) increased by approximately 65.6% and 34.4% following the application of 0.5% and 0.25% PA, respectively, compared to the control. The 0.5% PA enhanced the total weight of fruits by approximately 25.5%, while the 0.25% PA increased the elemental composition of the fruits. However, the highest PA concentration of 2% significantly (p > 0.05) reduced plant growth and yield, but significantly (p < 0.001) enhanced tomato fruit juice Brix, electrical conductivity, total dissolved solids, and titratable acidity. Additionally, total phenolic and flavonoid contents were significantly (p < 0.001) increased by the 2% PA. However, the highest carotenoid content was obtained with the 0.5% and 1% PA treatments. Additionally, PA treatment of the tomato plants resulted in a significantly (p < 0.001) high total ascorbate content, but reduced fruit peroxidase activity compared to the control. These indicate that PA can potentially be used as a biostimulant for a higher yield and nutritional quality of tomato.

Shading Nets Reduce Canopy Temperature and Improve Photosynthetic Performance in ‘Pinkerton’ Avocado Trees during Extreme Heat Events

Frequent extreme heat events cause major financial losses for the avocado industry. Shading nets are used to protect crops from harsh environmental hazards. To determine their ability to improve photosynthetic performance under extreme heat in avocado, we examined the impact of a resilient high-density silver 60% shading net on mature ‘Pinkerton’ avocado trees during such conditions. We hypothesized that reduced solar irradiation will lower canopy temperature and improve tree performance. During extreme heat events, photosynthetic photon flux density (PPFD), air temperature (Tair) and leaf temperature (Tleaf) reached 1188 μmol m−2 s−1, 43.1 °C and 43.8 °C in the control plots, respectively. In the net-covered plots, these parameters significantly decreased to 401 μmol m−2 s−1, 40.3 °C and 39.8 °C, respectively. Interestingly, leaf CO2 assimilation, stomatal conductance to water vapor (gs) and substomatal internal CO2 concentration (Ci) were significantly higher, by 94%, 120% and 13%, respectively, than in controls. On days with regular fall temperatures, PPFD, Tair and Tleaf reached 814 μmol m−2 s−1, 31.2 °C and 31.6 °C in the control plots, respectively. In the net-covered plots, these parameters significantly decreased to 291 μmol m−2 s−1, 29.5 °C and 29.4 °C, respectively. However, leaf CO2 assimilation was significantly (20%) lower, gs was similar and Ci was 10% higher than in control trees. These findings suggest that silver 60% shading nets may potentially reduce heat stress during extreme heat events, calling for long-term studies on their effects on flowering and fruit set, load, size and quality.

Biostimulant Effects of an Aqueous Extract of Duckweed (Lemna minor L.) on Physiological and Biochemical Traits in the Olive Tree

Biostimulants are becoming increasingly popular in agriculture for their ability to induce beneficial effects in crops, paving the way towards the identification of new materials with biostimulant potential. This study evaluated the potential of different concentrations of an aqueous extract (0.25%, 0.50%, and 1.00%, dry weight/water volume, respectively) obtained from duckweed (Lemna minor L.) to stimulate olive plants. Leaf net photosynthesis (Pn), leaf transpiration rate (E), stomatal conductance (gs), sub-stomatal CO2 concentration (Ci), chlorophyll content and other plant growth parameters were investigated. As a result, the extract improved Pn, gs, Ci, chlorophyll content and plant biomass production (leaf fresh and dry weight). Furthermore, the duckweed extract generally increased the uptake of nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe) and zinc (Zn), while it did not influence the content of sodium (Na), manganese (Mn) and copper (Cu). The untargeted metabolomic profiling of the extract revealed the presence of signalling compounds (including phytohormones), phenolics and glutathione. Such broad diversity of bioactives may support the stimulatory potential observed in olive. In summary, this study revealed for the first time that duckweed could be seen as a promising species to obtain extracts with biostimulant properties in olive trees.

Physiological, Biochemical and Defense System Responses of Roadside Vegetation to Auto-Exhaust Pollution.

This study determined the effects of traffic pollutants on plants (Nerium oleander and Ricinus communis) growing along Faisalabad to Okara (R-1) and Okara to Lahore (R-2) roads in Pakistan. The photosynthetic pigments, photosynthetic rate, transpiration rate and total soluble proteins of roadside vegetation were significantly lower than control plants (50m away from road). The average decrease in photosynthetic rate of Nerium oleander and Ricinus communis was 33.90% and 27.94% along R-1 and 41.85% and 32.409% along R-2 road, respectively. The decreased photosynthesis in roadside flora resulted in higher water use efficiency and substomatal CO2 concentration. However, higher antioxidant activity and free amino acid contents were noted in roadside plants that might be due to their defensive response to traffic pollutants. N. oleander was more affected by traffic pollutants and R.communis showed more resistance. Thus, N. oleander could be used for biomonitoring and R.communis for phytoremediation of vehicular pollution.

Physiological Characterization of Young 'Hass' Avocado Plant Leaves Following Exposure to High Temperatures and Low Light Intensity.

The worldwide demand for avocados has resulted in the planting of millions of young plants each year. However, global warming, resulting in high temperatures, sensed as heat stress, may severely damage these new plantings. The objective of this study was to assess the risks of heat stress on young avocado plants. We aimed to characterize different physiological parameters of young ‘Hass’ plant leaves following exposure to high temperatures under low light (LL) intensity and to pinpoint the temperature threshold for significant heat stress damage in these plants. To this end, young potted plants were subjected to different temperature gradients in a controlled-climate chamber. Minor and severe leaf damage was apparent in plants subjected to the 51 °C and 53 °C treatments, respectively. Minor and vast reductions in optimal quantum yield efficiency of photosystem II (Fv/Fm) values were observed in plants subjected to 51 °C and 53 °C, respectively. Heat stress treatments significantly reduced CO2 assimilation in plants subjected to 49 °C and higher temperatures. Stomatal conductance to water vapour and substomatal internal CO2 concentration were less sensitive to the heat treatments. These results imply that the heat damage threshold for young avocado plants under LL conditions is between 49 °C and 51 °C, whereas at 53 °C, severe and irreversible leaf damage occurs.

Correlative associations of photosynthetic and rooting attributes of sesame: Drought-induced reversed associations are corrected upon salicylic acid exposure

Concomitant rooting and photosynthetic responses of crop plants to water availability and plant growth regulators lack clarity. Three pot-grown sesame genotypes were subjected to three irrigation regimes, ranging from control to severe moisture stress, and two levels of salicylic acid (SA) (0 and 0.6 mM) to address this lacuna of data. Drought led to decreases in gas exchange, water relation, and rooting attributes, and shoot dry mass of the three genotypes in different extents, but it resulted in increases in substomatal CO2 concentration, proline concentration, and root/shoot dry mass. Cumulative root length, root length density, specific root length, and root surface tended to increase in genotype Yekta upon experiencing stress, in contrast to more or less decreasing tendencies in rooting characters of genotypes Shiraz and Naz-Takshakhe. Such genotype-specificity led to the reversal of correlations between gas exchange attributes and rooting characteristics under drought conditions. External SA led to enhancements in gas exchange, water relation, and rooting attributes, and dry mass; the degree of the enhancements tended to be greater in the stress-stricken plants. These findings indicate that genotype Yekta benefits from rooting characteristics with drought tolerance significance and SA is effective in enhancing photosynthetic, physiological and rooting attributes, drought tolerance, and growth of sesame under drought circumstances.

Effect of shading and high temperature amplitude in greenhouse on growth, photosynthesis, yield and phenolic contents of tomato (Lycopersicum esculentum Mill.).

The online version contains supplementary material available at 10.1007/s12298-021-01032-z.