Photosynthetic Characteristics and Antioxidative Metabolism of Flag Leaves in Responses to Nitrogen Application During Grain Filling of Field-Grown Wheat

Photosynthetic Pigments Content in Emmer Wheat Plants as Criteria of Productivity in Traditional and Organic Farming Technology

Background. Estimation of chlorophyll and carotenoid content is an informative way to obtain ideas about the plants photosynthetic process and is an indirect method for assessing the productivity of plant crops, including cereals. As the worldwide interest at now for traditional and natural foods is growing, in the work we used one of the oldest grain crops – emmer wheat (Triticum dicoccum (Schrank.) Schuebl.) which was cultivated in traditional and organic farming system. Objective. The study aim was to determine the role of chlorophyll and carotenoids in the emmer wheat productivity formation by traditional and organic farming technology under different pre-sowing seed treatment systems. Methods. Field experiment was establishment during 2019–2021 on low-humus, hard-loam chernozems, the condition of which meets the “virgin land” criterion. The emmer wheat cultivation in organic technology was carried out in crop rotation: winter rye (green manure crop) – mustard (to improve the field phytosanitary condition and soil organic matter indicators) – emmer wheat. Two variants of pre-sowing seed treatment were studied: irradiation with ultraviolet light of the C range (100–280 nm) and seed treatment with 1r Seed Treatment humic preparation. The pre-sowing seed treatment in the traditional technology of the emmer wheat cultivation was carried out by the UV-C irradiation. In organic technology both UV-C irradiation and treatment with 1r Seed Treatment humic preparation of natural origin were used. Statistical data processing was performed by methods of descriptive statistics, regression and analysis of variance by the program Statistica 10.0. The experimental data significance was evaluated by using multifactor analysis of variance (ANOVA) to calculate the least significant difference (LSD05). Results. It was found the use of UV-C seeds irradiation in organic and traditional cultivation technologies leads to increase in the chlorophyll a (Chl a) content by 9.2 % and chlorophyll b (Chl b) content by 14.5 % in plants grown by organic technology, however to decrease in carotenoid content (Ct) by 14.9 %. The increase in the photosynthetic pigments content by UV-C seeds irradiation lead to yield increase from 4.26 t/ha by the traditional technology to 5.17 t/ha by the organic technology, ie by 21.4 %. In organic technology based on the comparison of the photosynthetic apparatus main indicators of the emmer wheat and yield, the most effective method for seed treatment was determined. It was established that at result of 1r Seed Treatment humic preparation application in pre-sowing seed treatment, the Chl a concentration decreased by 2.4 %, the Chl b and Ct concentration increased by 5 and 25.5 %, respectively, compared with plants grown from UV-C irradiated seeds. When 1r Seed Treatment was used for pre-sowing treatment yield was 5.58 t/ha, while at UV-C seed treatment – 5.17 t/ha, ie, the yield increase was 8 %. An inverse correlation between the ratio of the photosynthetic pigments Chl a/Chl b content and the emmer wheat yield was determined. Conclusions. According to the study results, it can be assumed that the introduction of organic farming technology with pre-sowing seed treatment by the 1r Seed Treatment humic preparation can increase the emmer wheat yield by 31% compared to the traditional technology. Thus, the photosynthetic pigments content and their ratio can be the effectiveness indicators of the implemented agricultural technologies.

Impact of Nitrogen Addition on Physiological, Crop Total Nitrogen, Efficiencies and Agronomic Traits of the Wheat Crop under Rainfed Conditions

Optimizing nitrogen (N) application timings and rate can improve nutrient uptake and nutrient efficiencies in wheat, particularly under rainfed conditions. Climatic stress in the form of high temperature and drought resulted in the decreased crop physiological traits, hastened maturity and, ultimately, caused lower grain yield. The impact of N application rates as full and split dose at three diverse locations of rainfed Pothwar, Pakistan was studied through field experiments for two years (2013–14 and 2014–15). Treatments include T1 = control (no fertilizer applied), full dose of N applied at the time of crop sowing, i.e., T2 = 50 kg N ha−1, T3 = 100 kg N ha−1 and T4 = 150 kg N ha−1, and split application of N at different timings at different stages of the crop, called split application of N, i.e., T5: application of 50 kg N ha−1 (15 kg N ha−1 (sowing, BBCH (Biologische Bundesanstalt Bundessortenamt und Chemische Industrie) 0): 20 kg N ha−1 (tillering, BBCH20): 15 kg N ha−1 (anthesis, BBCH 60), T6: application of 100 kg N ha−1 (30 kg N ha−1 (sowing, BBCH 0): 40 kg N ha−1 (tillering, BBCH 20): 30 kg N ha−1 (anthesis, BBCH 60) and T7: application of 150 kg N ha−1 (45 kg N ha−1 (sowing, BBCH 0): 60 kg N ha−1 (tillering, BBCH 20): 45 kg N ha−1 (anthesis, BBCH 60). The three study sites were Islamabad (high rainfall with optimum temperature), University Research Farm (URF)-Chakwal Road, Koont (medium rainfall with moderate temperature), and Talagang (low rainfall with high temperature). Results revealed that the highest stomatal conductance (0.80 mole H2O m−2 s−1), net photosynthetic rate (20.07 μmole CO2 m−2 s−1), transpiration rate (9.58 mmole H2O m−2 s−1), intercellular CO2 concentration (329.25 μmole CO2 mol−1 air), SPAD values (58.86%) and proline contents (35.42 μg g−1) were obtained from split application of N (T6 = split N100) compared to control and full dose N treatments. Among the sites, these physiological traits remained highest at Islamabad and lowest at Talagang, while between the years, the maximum values of the measured parameters were obtained during 2013–14. A similar trend was observed for crop total N, N efficiencies, and agronomic traits of the crop. The results suggested that the optimum N application rate at appropriate timings can help to harvest the real benefits of N. The split dose resulted in the maximum performance of the crop from the physiological parameters to the agronomic traits of the crop.

Response of Chlorophyll, Carotenoid and SPAD-502 Measurement to Salinity and Nutrient Stress in Wheat (Triticum aestivum L.)

Abiotic stress can alter key physiological constituents and functions in green plants. Improving the capacity to monitor this response in a non-destructive manner is of considerable interest, as it would offer a direct means of initiating timely corrective action. Given the vital role that plant pigments play in the photosynthetic process and general plant physiological condition, their accurate estimation would provide a means to monitor plant health and indirectly determine stress response. The aim of this work is to evaluate the response of leaf chlorophyll and carotenoid (Ct) content in wheat (Triticum aestivum L.) to changes in varying application levels of soil salinity and fertilizer applied over a complete growth cycle. The study also seeks to establish and analyze relationships between measurements from a SPAD-502 instrument and the leaf pigments, as extracted at the anthesis stage. A greenhouse pot experiment was conducted in triplicate by employing distinct treatments of both soil salinity and fertilizer dose at three levels. Results showed that higher doses of fertilizer increased the content of leaf pigments across all levels of soil salinity. Likewise, increasing the level of soil salinity significantly increased the chlorophyll and Ct content per leaf area at all levels of applied fertilizer. However, as an adaptation process and defense mechanism under salinity stress, leaves were found to be thicker and narrower. Thus, on a per-plant basis, increasing salinity significantly reduced the chlorophyll (Chlt) and Ct produced under each fertilizer treatment. In addition, interaction effects of soil salinity and fertilizer application on the photosynthetic pigment content were found to be significant, as the higher amounts of fertilizer augmented the detrimental effects of salinity. A strong positive (R2 = 0.93) and statistically significant (p < 0.001) relationship between SPAD-502 values and Chlt and between SPAD-502 values and Ct content (R2 = 0.85) was determined based on a large (n = 277) dataset. We demonstrate that the SPAD-502 readings and plant photosynthetic pigment content per-leaf area are profoundly affected by salinity and nutrient stress, but that the general form of their relationship remains largely unaffected by the stress. As such, a generalized regression model can be used for Chlt and Ct estimation, even across a range of salinity and fertilizer gradients.

Effects of nitrogen stress on the photosynthetic CO2 assimilation, chlorophyll fluorescence, and sugar-nitrogen ratio in corn

A field experiment was conducted using three corn cultivars (Jingyu7, Nongda80, and Tangyu10) and three nitrogen (N) application rates (0, 75, and 150 kg N ha(-1)). The objectives of this study were to investigate the responses of photosynthetic CO2 assimilation (Ph), the maximum quantum yield of photosystem II (Fv/Fm), leaf dry weight (LDW), leaf nitrogen concentration (LNC), leaf sugar concentration (LSC), and the sugar-to-nitrogen concentration ratio (S/N) to N levels in three different field-grown corn cultivars on three sampling dates. The results showed that the LDW, Fv/Fm, Ph, LNC, and LSC increased with increasing N levels, and the variation patterns of Fv/Fm, Ph, and LNC were "low-high-low". In contrast, S/N decreased with increasing N levels, and its variation pattern was "high-low-high". The values of LDW, Fv/Fm, Ph, LNC, LSC, and S/N were greatest under high N conditions, followed by medium N conditions, and finally low N conditions. Significant interactions occurred between Ph, Fv/Fm, LNC, LSC, LDW, and S/N, with the exception of the interaction between LSC and S/N and between LSC and LDW. The correlation coefficients between Ph and S/N and between Fv/Fm and S/N were -0.714 and -0.798, respectively.

Comparative changes in the antioxidant system in the flag leaf of early and normally senescing near-isogenic lines of wheat (Triticum aestivum L.)

The antioxidant system was significantly inhibited in the early aging line than the near-isogenic normal aging line during senescence. The antioxidant system plays pivotal roles in removal of reactive oxygen species (ROS) produced during leaf senescence. To explore its roles in leaf senescence of wheat (Triticum aestivum L.), the concentrations of antioxidants, activities, and gene expression of antioxidant enzymes were evaluated in flag leaves of the early aging line (EAL) and the near-isogenic normal aging line (NL) during senescence. The results showed that the total chlorophyll and soluble protein in the EAL declined earlier and faster, while more malondialdehyde and ROS accumulated compared with the NL. The activities of superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase were lower in the EAL than in the NL across multiple measuring dates. Additionally, the EAL had less amounts of reduced ascorbate and glutathione as well as lower reduction state with the progression of senescence. Concomitantly, the gene expression of antioxidant enzymes in the EAL was also significantly repressed relative to those in the NL during natural senescence. Taken together, the earlier onset and faster rate of senescence in the EAL could be a result of an imbalance of ROS production and ROS-scavenging antioxidant system, which provided valuable hints toward understanding leaf senescence of wheat.