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The effects of nitrogen and phosphorus levels on the physiological traits, yield, and seed yield of rapeseed (Brassica napus L.), were studied in a farm research project of Zanjan University. Three levels of nitrogen (0, 100, and 200 kg/ha) and three levels of phosphorus (0, 75, and 150 kg/ha) were considered. The results showed that an increase in nitrogen level caused an increase in the leaf chlorophyll content so that the application of 200 kg/ha of nitrogen increased the chlorophyll content of the leaves until the mid-grain filling stage. Nitrogen application lowered leaf stomatal conductance in the early flowering stage whereas the stomatal conductance was increased during the late flowering stage. Nitrogen application (100 and 200 kg/ha) also increased the quantum yield of photosystem II. On the other hand, with the application of 150 kg/ha and 75 kg/ha of phosphorus, the leaf stomatal conductance and the quantum yield of photosystem II in the early flowering stage increased respectively. The results showed that the application of 200 kg/ha of nitrogen and 75 kg/ha of phosphorus significantly increased seed and oil yield compared to the control. In addition, the number of siliques per plant and the weight of 1000 seeds showed an increasing trend that was affected by nitrogen and phosphorus levels. This study demonstrated that nitrogen enhanced the chlorophyll content, leaf area, and consequently, the quantum yield of photosystem II. Nitrogen also augmented the seed filling duration, seed yield, and oil yield by increasing gas exchange. As a result, the application of 100 kg/ha of nitrogen together with 75 kg/ha phosphorus showed the greatest effect on the qualitative and quantitative yield of rapeseed. However, the application of 200 kg/ha of nitrogen alone or in combination with different levels of phosphorus did not significantly increase many of the studied traits.

Zinc deficiency is one of the most widespread nutritional problems, affecting nearly one-third of the world population. In addition, it is known that zinc deficiency not only reduces crop yield but also its quality. The effect of different methods of zinc application on the growth, yield, and quality of safflower seeds under regular irrigation and interruption of irrigation from flowering to harvest (82 and 80 DAS in the first and second years, respectively) was evaluated. Zinc sulfate was applied in both soil and foliar methods. The zinc sulfate treatments include no zinc sulfate, soil application of 20, 40, and 60 kg ha−1 at the planting stage; spraying 2.5, 5, and 7.5 g L−1 in the rosette stage; and spraying 2.5, 5, and 7.5 g L−1 in the flowering stage. The end-season drought caused a decrease in the chlorophyll index, leaf area index, relative water content, plant height, yield components, biological yield, seed yield, harvest index, seed oil content, oil harvest index, and seed element content compared to regular irrigation. The decrease in yield occurred with a decrease in the capitol number and diameter, seed number per capitol, and 1000-seed weight. The severity of the damage of the end-season drought stress in the second year was higher than in the first year due to the higher temperatures and the decrease in the rainfall. In both years, the application of zinc sulfate in different ways had an increasing effect on the studied traits in both normal and stress conditions. The application of zinc sulfate reduced the negative effects of unfavorable environmental conditions and improved the yield and nitrogen, phosphorus, potassium, zinc, and iron element content in the seed. In both application methods of zinc sulfate, the increment in the zinc sulfate concentration decreased the seed phosphorus content. However, the phosphorous content was more than that of the treatment of non-zinc application. The application of zinc increased the biological, seed, and oil yield of the treated plants, but the seed and oil yield were more affected. This effect was shown in the seed and oil harvest index increment. Under regular irrigation, higher concentrations of zinc sulfate enhanced plant performance, but under stress conditions, medium and lower concentrations were more effective. The highest 1000-seed weight and potassium and zinc content were obtained by spraying zinc sulfate at 5 g L−1 in the flowering stage under normal irrigation conditions. A comparison of the two methods of applying zinc sulfate showed that foliar spraying was more effective than soil application in improving the seed yield. The soil application is more effective on biological yield than seed yield.

Heavy metal contamination of arable land is an increasing problem for crop production and food safety. The effect of salicylic acid (SA) on crop performance depends not only on the plant species, but also on the concentration of SA and the method of application. The effects of exogenous application of SA at concentrations of 0, 750 and 1500 µM by foliar spraying and seed priming methods were investigated on maize plants under lead and zinc stress. Heavy metal stress significantly reduced photosynthetic parameters and pigment levels, with the greatest reduction observed under the combined application of these metals (Jan and Parray Jan, S., Parray, J.A. (2016) Heavy metal uptake in plants. In Approaches to Heavy Metal Tolerance in Plants; Springer: Singapore, 1–18. 10.1007/978-981-10-1693-6_1). Comparison of photosynthetic rates during early growth and tasseling showed that under unstressed conditions, photosynthesis increased markedly as the plants developed. On the other hand, under stressed conditions, photosynthesis decreased over time. This decrease was less pronounced when metals were applied individually, but significantly more pronounced when they were applied in combination. The application of SA mitigated the effects of heavy metal stress. Comparison of application methods showed that seed priming was more effective than foliar spraying in the early growth stage. However, there were no significant differences between these methods at the tassel stage. Hydropriming and distilled water spraying showed no advantage over the control treatment. Heavy metal stress reduced leaf area, stomatal size, vascular bundle and mesophyll cell diameter and plant biomass, while increasing stomatal frequency and leaf thickness. Although the relative water content (RWC) of plants under stress conditions decreased, SA application alleviated this damage. The decrease in RWC was accompanied by an increase in stomatal resistance and leaf temperature. This reduction in RWC could be due to a decrease in vascular diameter and water flow to the leaves. The reduction in stomatal closure and transpiration rate under stress conditions can be considered as a water saving mechanism. Salicylic acid, especially at the highest concentration, improved plant performance and increased maize biomass. This improvement was attributed to the increase in photosynthetic pigment content, photosynthetic rate and leaf area expansion. The increase in leaf area and decrease in leaf thickness with SA application indicate further development of leaf cell size and leaf expansion.

Nitric oxide (NO) is recognized as an endogenous signaling molecule that plays an important role in the defence responses of medicinal plants to NaCl stress. In this study, we investigated the effects of sodium nitroprusside (SNP) as an NO donor at three concentrations (0, 100, and 200 µmol l −1 ) to alleviate the deleterious effects of salt stress (100 mM NaCl) on leaf gas exchange and biochemical characteristics of Silybum marianum L. seedlings. This study showed that salt stress significantly decreased relative water content (RWC), chlorophyll b content, endogenous NO concentration, maximum quantum yield (Fv/Fm), leaf gas exchange, stomatal size, K + /Na + ratio, and plant dry weight, and increased malondialdehyde (MDA) content, hydrogen peroxide (H 2 O 2 ) content, proline content, stomatal density, and enzyme activities. SNP treatment increased Fv/Fm, photosynthetic pigments, K + /Na + ratio, and dry weights of the shoots and roots of NaCl-exposed plants. The exogenous application of NO increased the proline content under salinity stress more than under stress conditions without SNP application, so that the proline content increased from 32 to 47 µmol g −1 . Application of 100 µM SNP also increased endogenous NO concentration (up to 43%) and consequently protected plants against salt stress-induced damage by improving enzyme activity and reducing the H 2 O 2 generation rate (up to 14%) and MDA content (up to 50%) compared to plants treated with NaCl alone. Foliar application of NO to salt-stressed plants increased root and shoot respiration rates from 20 and 12%, respectively, under salinity stress to 57% under the application of SNP and stress conditions, and decreased stomatal conductance by up to 70%, resulting in improved RWC. Increased internal NO generation in plants induced by 100 µM SNP application has the potential to mitigate salinity injury in Silybum marianum L. plants.