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Aim This investigation aims to study the effect of biochar on gas exchange, water relations and photosynthetic pigments of European yew (Taxus baccata) seedling in different light intensities (LI).
Materials and Methods Two-year potted seedlings of European yew are placed in forest stands with canopies of closed (15% LI), semi-closed (45% LI) and open (75% LI). In late June 2018, biochar was added to potted soils at the levels of zero, 10, 20 and 30 g.kg^-1 and until the end of November, every 3 (or 4) days 100 mL water was given to each pot.
Findings Seedling survival at different levels of treatments was 100%. Regardless of biochar, the highest photosynthesis, stomatal conductance, intercellular CO₂ concentration, relative water content, chlorophyll (chl) contents in closed canopy, and the highest leaf temperature in open canopy was observed. With increasing biochar concentration, chl b and total chl increased (28-86%, respectively) in open canopy and decreased (28 and 28%, respectively) in closed canopy. Neither biochar nor LI affected significantly electrolyte leakage and carotenoid content.
Conclusion Although yew seedlings were able to maintain their vegetative quality and health in different LI, and the measured variables responded differently to light-biochar combination, it may be best to grow yew in shade together with biochar. Since, the effect of biochar becomes more tangible over time, further research in next years can lead to more accurate findings affected by the combined light-biochar treatment.

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Aim: Caspian locust, native to Hyrcanian forests of Iran, is one of the pioneer species, which it distributed in the moist soils of these forests. So far, the response of its seedlings to permanent and temporary flooded beds has not been reported. This study was conducted with the objective to analyze the physiological responses of Caspian locust seedlings to flooding and flooding-recovery conditions.

Materials & Methods: Flooding conditions were examined for 90 days in the greenhouse of the Tarbiat Modares University. The study was carried out in a factorial experiment as a completely randomized design with 5 treatments and 4 replications. Treatments included: (1) continuous flooding for 90 days (F90), (2) flooding for 60 days followed by a 30-day recovery (F60+R30), (3) flooding for 45 days followed by a 45-day recovery (F45+R45), (4) flooding for 30 days followed by a 60-day recovery (F30+R60) and (5) Control.
Findings: Results showed that flooding for 90 days induced a significant decrease in net photosynthesis (-91%), stomatal conductance (-77%), transpiration (-81%), Chl a (-63%), Chl b (-67%) and Chl _Tot (-64%) compared to the control (p<0.05). When flooding was removed for 30-60 days, plants were able to recover gas exchange activities from 30 to 90% and Chl content by 55-90%.
Conclusion: Based on our results, seedlings of G. caspica can survive and grow throughout a medium period of soil waterlogging. Therefore, Caspian locust appears to be a promising species for reforestation programs in the riverine areas and temporarily flooded wetlands.
 

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Intra-specific variation in responses of diurnal and long-term photosynthesis, stomatal conductance, chlorophyll fluorescence, and respiration in spring wheat (Triticum aestivum L.) to salinity was investigated using two tolerant cultivars (CR and Kharchia-65) and a sensitive one (Ghods). Plants were grown in sand culture in controlled environment at selected levels of salinity (5 as control, 100, 200, and 300 mol m-3 NaCl and CaCl2 in 5:1 molar ratios). Photosynthesis was markedly reduced in the saline conditions, but there were no significant differences observed amongst cultivars. Stomatal conductance of both upper and lower leaf surfaces was the main factor limiting photosynthesis in the presence of salinity. However, non-stomatal limitations as indicated by reduction in variable to maximum fluorescence (Fv/Fm) showed that plants might experience some degree of photoinhibition at the highest level of salinity. Gas exchange in control and 100 mol m-3 did not change throughout the day in either the salt-sensitive or the salt tolerant cultivars but in the last hours of the day photosynthesis in the sensitive cultivar was markedly reduced. Respiration remained unchanged up to 200 mol m-3 salinity but at 300 mol m-3 it decreased as compared with the lower salinity levels. The most remarkable change in respiration rate was that at seven hours after light when CO2 production was much higher than at the other times of the day. The results indicated that although photosynthesis is well correlated with stomatal conductance, wheat genotypes show different responses as regards other such aspects of photosynthesis, in different salt concentrations, as growth stage, time of the day and duration of salt exposure.

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It is suggested that cultivars of wheat (Triticum aestivum L.) with regulated growth and development would be able to produce higher yields under water-limited conditions, which is crucial in future food production. Water use efficiency (WUE) is worthy of exploration in this regard. In this study, the effects of nitrogen fertilizer levels (0, 40 and 80 kg Nha-1) and a plant growth retardant (Chlormequat Chloride = CCC) on WUE of four dryland wheat cultivars (Agosta, Nicknejad, Azar-2 and Fin-15) were examined in a field experiment during 2006-07 and 2007-08 growing seasons at College of Agriculture, Shiraz University, Iran. The results showed that there existed significant differences between cultivars for grain yield, biomass and WUE. In the first season, the highest grain yield and biomass production (192.4 and 431.2 gm-2, respectively) were obtained from Nicknejad cultivar, CCC application and using 80 kg Nha-1, and in the second season, from Azar-2 cultivar (121.5 and 333.5 gm-2, respectively). CCC and nitrogen had significant effects on photosynthesis rate and WUE in both seasons. Interaction of CCC and 80 kg Nha-1 on WUE were significant in both seasons (1.24 and 2.72 gm-2mm-1, respectively). It is suggested that interactive application of CCC and nitrogen fertilizer could have beneficial effects on wheat grain yield under similar agro-climatic conditions.

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A factorial pot experiment based on randomized complete blocks design with four replications was carried out in order to evaluate salt tolerance of four sugar beet cultivars including Madison (British origin) and three Iranian cultivars (7233-P12, 7233-P21 and 7233-P29) using carbon isotope discrimination (Δ). Plants were grown in sand culture medium in greenhouse conditions. Sugar beet cultivars were irrigated with saline water (tap water as control, 50, 150, 250 and 350 mM of NaCl and CaCl2 in 5: 1 molar ratio) from 4-leaf stage for 16 weeks. Carbon isotope discrimination significantly decreased with increasing salinity. Significant differences of Δ between shoot and root were observed in all cultivars and all levels of salinity. Madison cv. showed lower Δ in shoot and root than the other three cultivars at all levels of salinity except the control, but cv. 7233-P29 had significantly higher Δ values at saline conditions of 150 mM and above. Although the regression of Δ and Ci/Ca was positive, the slope of regression line was different from the pattern predicted by theory, indicating an underestimation of Δ in these samples. Relatively higher 13C (lower Δ) was found in root as compared with shoots.

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This study was conducted under Ahvaz, Iran environmental condition during 2012 and 2013 growing seasons in order to investigate the influence of foliar application of potassium on some physiological and biochemical characteristics of three olive cultivars including ‘Mission’, ‘Koroneiki’ and ‘Dezfuli’. Potassium sulfate in different concentrations of 0, 1, and 2 g l^-1 was sprayed twice on selected mature 10 year old trees; at 50 and 65 days after full bloom. Potassium sprays increased leaf chlorophyll content of all cultivars, leaf potassium content in ‘Mission’ and ‘Koroneiki’ cvs., fruit anthocyanin concentration of ‘Dezfuli’ in two crop seasons. However, K treatments had no significant effect on leaf N and P content, fruit K and P content in all studied cultivars. Fruit soluble carbohydrates increased by foliar application of potassium in ‘Koroneiki’ and ‘Dezfuli’ cultivars in the second year of study. Stem water potential and leaf stomatal conductance were significantly affected by cultivar and K treatments during the two years. Our findings showed that foliar application of potassium resulted in the decrease of stomatal conductance of ‘Koroneiki’ and ‘Dezfuli’ in two crop seasons. Based on the results, it can be concluded that the studied cultivars differently respond to K treatments during the two crop seasons and foliar potassium application could have a positive impact on leaf chlorophyll, leaf potassium, fruit soluble carbohydrates and fruit anthocyanins in olive cultivars.

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Effects of salinity (0, 2, 6, and 8 dS m^-1) on some photosynthetic parameters and morphological characteristics of 3 almond cultivars (‘Tuono’, ‘Shoukofeh’ and ‘Sahand’), with or without Salicylic Acid (SA) treatment (at 0, 1 and 2 mM), were studied in a factorial experiment using the completely randomized design with 3 replications, in a greenhouse experiment. Results revealed that while SA at 1 mM significantly improved morphological and photosynthetic properties of salinized plants, its relatively higher concentration (2 mM) impaired growth and photosynthetic attributes. Of the tested cultivars, Shokoufeh grafted on the GF677 rootstock showed higher salt tolerance than the others. This study provides convincing evidence with regard to the potential of SA in improving almond plant growth under salt stress; suitable concentrations of SA when added to saline situations helped the plants in osmotic adjustment for alleviating the harmful effects of salinity. Efficacy of SA may be tested under field conditions before recommending it as a practical tool to enhance almond plant performance in saline soils.
 

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This experiment was conducted to determine the effects of dust, rain, and pollination on photosynthesis activity and crop yield of commercial date palm (Phoenix dactylifera L.) cultivar `Sayer’. Mature trees were used for dust treatments application and assessments under Ahvaz, Iran, during the 2016-2017 growing seasons. The dust blew on the trees canopy using a blower and the leaf gas exchange was evaluated using an infrared gas analyzer on the intact leaves. After treatments, photosynthesis rate, transpiration rate, and stomatal conductance were measured. The leaf gas exchange results showed significant differences between the applied combined treatments on photosynthesis rate (from 9.18 to 0.64 μmol CO₂ m^-2s^-1), stomatal conductance (from 39.9 to 6.67 mmol m⁻²s⁻¹), and transpiration rate (from 2.78 to 1.49 mmol H₂O m^-2s^-1). Deposition manner of dust particles, the number of stomata in the abaxial and adaxial surfaces of leaflets, and the minimum dust-carrying capacity (MDCC) were determined using scanning electron microscopy (SEM). Stomata study using SEM showed that date palm leaflet surfaces are almost wavy and the stomata are situated in the concave surfaces in a linear arrangement on both abaxial and adaxial leaf surfaces. Although, there were no significant differences in stomatal density at the abaxial (299 mm^-2) and adaxial (300 mm^-2) leaf surfaces, the leaflet position within the leaf showed a significant influence on MDCC. The base positioned leaflets in the leaf showed the highest (2.5 mg cm^-2) and the upper positioned top leaflets showed the lowest MDCC (1.7 mg cm^-2), respectively. Also, SEM showed a sign of covering or entering dust particles into the stomata with possible stomata clog and blockage lead to the significant reduction of photosynthesis and crop yield. Besides, pollinated trees showed the maximum crop yield (59.17 Kg tree^-1), so the minimum yield was recorded on un-pollinated palm trees (1.90 Kg tree^-1).  

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Gerbera is one of the significant cut flower crops worldwide suffering from loss of flower quality induced mainly by Calcium (Ca) deficiency. In this research, the influence of Humic Acid (HA) and Ca in nutrient solution was studied on the growth parameters of gerbera. A completely randomized hydroponic experiment was designed by adding HA (0, 100, 500, and 1,000 mg L^-1) and Ca (3.5 and 7 meq L^-1 nutrient solution) to the nutrient solution of gerbera, with three replications. The effects of the treatments were evaluated on the growth, protein content, proline content, transpiration, CO₂ assimilation, photosynthesis, SPAD value, number of harvested flower, and antioxidant activity in gerbera cv. Malibu. Results showed that decreasing Ca level to 3.5 meq L^-1 decreased Superoxide Dismutase (SOD), Peroxidase (POD), and CO₂ assimilation. However, this treatment caused an increase in Malondialdehyde (MDA), protein content, proline content, chlorophyll, and photosynthesis. Transpiration and number of harvested flowers were not affected by Ca concentration significantly. The highest level of HA (1,000 mg L^-1) increased POD and transpiration (30 and 11%, respectively). However, SOD and protein content increased at 500 and 1,000 mg L^-1 HA levels. When HA was accompanied with Ca, SPAD value, transpiration, and CO₂ assimilation were improved, especially at high levels of HA (500 and 1,000 mg L^-1) and higher level of Ca (7 meq L^-1 Ca). The results suggested that HA could increase the number of harvested flowers and improve plant health by enhancing the plant enzymatic antioxidant defense system.