Heat Stress Prevented the Biomass and Yield Stimulation Caused by Elevated CO2 in Two Well-Watered Wheat Cultivars

To investigate the interactive effects of elevated CO2 and heat stress (HS), we grew two contrasting wheat cultivars, early-maturing Scout and high-tillering Yitpi, under non-limiting water and nutrients at ambient (aCO2, 450 ppm) or elevated (eCO2, 650 ppm) CO2 and 22°C in the glasshouse. Plants were exposed to two 3-day HS cycles at the vegetative (38.1°C) and/or flowering (33.5°C) stage. At aCO2, both wheat cultivars showed similar responses of photosynthesis and mesophyll conductance to temperature and produced similar grain yield. Relative to aCO2, eCO2 enhanced photosynthesis rate and reduced stomatal conductance and maximal carboxylation rate (Vcmax). During HS, high temperature stimulated photosynthesis at eCO2 in both cultivars, while eCO2 stimulated photosynthesis in Scout. Electron transport rate (Jmax) was unaffected by any treatment. eCO2 equally enhanced biomass and grain yield of both cultivars in control, but not HS, plants. HS reduced biomass and yield of Scout at eCO2. Yitpi, the cultivar with higher grain nitrogen, underwent a trade-off between grain yield and nitrogen. In conclusion, eCO2 improved photosynthesis of control and HS wheat, and improved biomass and grain yield of control plants only. Under well-watered conditions, HS was not detrimental to photosynthesis or growth but precluded a yield response to eCO2.

Impacts of Fertilization Optimization on Ammonia Volatilization, Soil Nitrification, Denitration Intensity From Wheat Fields and Nitrogen Utilization Under Water-saving Irrigation

Scholars have proposed the practice of split N fertilizer application (SNFA), which has proven to be an effective approach for enhancing N use efficiency. However, the effect of SNFA on NH3 volatilization, nitrification and denitration in soil, remain largely unknown. As such, the current study assessed soil NH3 volatilization, nitrification and denitrification intensities, abundance of nitrogen cycle-related funetional genes, and invertase activity for different treatments. We applied a rate of 240 kg·ha-1 of N, and the following fertilizer ratios of the percent base to that of topdressing under water-saving irrigation: N1 (basal/dressing, 100%/0%), N2 (basal/dressing, 70%/30%), N3 (basal/dressing, 50%/50%), N4 (basal/dressing, 30%/70%), and N5 (basal/dressing, 0%/100%). N3 treatment resulted in a significant decrease in rate of NH3 volatilization. This treatment also significantly reduced nitrification and denitrification intensities, primarily owing to the reduced functional genes abundance involved in the nitrogen cycle (Amoa-AOB, nirK and nirS) and reduced invertase activity (urease, nitrate reductase, nitrite reductase) in wheat-land soil. 15N tracer studies further demonstrated that N3 treatments significantly increased the grain nitrogen accumulation by 9.50-28.27% compared with that under other treatments. This increase was primarily due to an increase in the amount of N absorbed by wheat from soil and fertilizers, which was caused by an enhancement in total N uptake (7.2-21.81%). Collectively, these results suggest that the N3 treatment (basal/dressing, 50%/50%) improves N uptake by wheat, reduces the soil NH3 volatilization rate, and has the potential to reduce the amount of N2O generated by nitrification and denitrification.

Heat stress prevented the biomass and yield stimulation caused by elevated CO2 in two well-watered wheat cultivars

To investigate the interactive effects of elevated CO2 and heat stress (HS), we grew two contrasting wheat cultivars, early-maturing Scout and high-tillering Yitpi, under non-limiting water and nutrients at ambient (aCO2, 450 ppm) or elevated (eCO2, 650 ppm) CO2 and 22°C in the glasshouse. Plants were exposed to two 3-day HS cycles at the vegetative (38.1°C) and/or flowering (33.5°C) stage. At aCO2, both wheat cultivars showed similar responses of photosynthesis and mesophyll conductance to temperature and produced similar grain yield. Relative to aCO2, eCO2 enhanced photosynthesis rate and reduced stomatal conductance and maximal carboxylation rate (Vcmax). During HS, high temperature stimulated photosynthesis at eCO2 in both cultivars, while eCO2 stimulated photosynthesis in Scout. Electron transport rate (Jmax) was unaffected by any treatment. eCO2 equally enhanced biomass and grain yield of both cultivars in control, but not HS, plants. HS reduced biomass and yield of Scout at eCO2. Yitpi, the cultivar with higher grain nitrogen, underwent a trade-off between grain yield and nitrogen. In conclusion, eCO2 improved photosynthesis of control and HS wheat, and improved biomass and grain yield of control plants only. Under well-watered conditions, HS was not detrimental to photosynthesis or growth but precluded a yield response to eCO2.

Development of wheat plants coinoculated with rhizobium strains

ABSTRACT This study aimed to evaluate the efficiency of diaztrophic bacteria coinoculation in wheat cultivars grown in Cerrado Oxisol. A randomized block design was used, with a 13 x 3 factorial scheme and four replicates. The treatments consisted of inoculation with Azospirillum brasilense (strains AbV5 and AbV6 strains combined) and coinoculation with Bradyrhizobium japonicum (strains SEMIA 5079 and SEMIA 5080 combined, and strain BR3267), as well as Rhizobium tropici (strains MT08 and MT15) and R. leguminosarum (strain MT16) combined or in isolation, tested in wheat cultivars BRS 394, BRS 264 and BRS 254. The variables analyzed were grain nitrogen concentration and accumulation and crude protein content, 100-grain weight and total grain mass. The treatment containing the commercial cowpea inoculant showed a higher total grain mass (5.8766 g). Interaction was observed for grain nitrogen concentration, particularly for A. brasilense + MT 15 (R. tropici) and MT 15 in wheat cultivar BRS 264. Coinoculation with diazotrophic bacteria isolated from leguminous plants shows potential for use in wheat cultivars.

The Effect of Increased Ozone Levels on the Stable Carbon and Nitrogen Isotopic Signature of Wheat Cultivars and Landraces

Several studies have highlighted the negative effects of ozone (O3) on wheat development and productivity. The negative effects of O3 are mediated by changes in photosynthetic carbon and nitrogen metabolism, which are difficult and time-consuming to assess and are thus only measured sporadically throughout the plant cycle. Stable isotope measurements in grains can help integrate the effects of chronic O3 exposure over the lifespan of the plant. This particular study focuses on the extent to which the stomatal conductance and productivity of Mediterranean wheat are related to carbon and nitrogen isotopic signatures under chronic O3 exposure. An open top chamber experiment was designed to analyse the effects of the pollutant on 12 Spanish wheat genotypes, which included modern cultivars, old cultivars and landraces. Four O3 treatments were considered. Stomatal conductance (gs) measurements were carried out during anthesis, and yield and nitrogen content parameters were taken at maturity, along with the carbon (δ13C) and nitrogen (δ15N) isotopic composition measured in grains. Modern and old cultivars responded similarly to O3 and were sensitive to the pollutant regarding yield parameters and gs, while landraces were more O3-tolerant. Grain δ13C had a strong negative correlation with grain yield and stomatal conductance across genotypes and O3 conditions, and increased under higher O3 concentrations, showing its capacity to integrate O3 stress throughout the wheat cycle. Meanwhile, a higher nitrogen concentration in grains, coupled with smaller grains, led to an overall decreased grain nitrogen yield under higher O3 concentrations. This nitrogen concentration effect within the grain differed among genotypes bred at different ages, following their respective O3-sensitivity. δ15N showed a possible indirect effect of O3 on nitrogen redistribution, particularly under the highest O3 concentration. The correlations of δ15N and δ13C to the usual effects of ozone on the plant suggest their potential as indicators of chronic ozone exposure.

Optimized nitrogen fertilizer application strategies under supplementary irrigation improved winter wheat (Triticum aestivum L.) yield and grain protein yield

Background Exploring suitable split nitrogen management is essential for winter wheat production in the Huang-Huai-Hai Plain of China (HPC) under water-saving irrigation conditions, which can increase grain and protein yields by improving nitrogen translocation, metabolic enzyme activity and grain nitrogen accumulation. Methods Therefore, a 2-year field experiment was conducted to investigate these effects in HPC. Nitrogen fertilizer was applied at a constant total rate (240 kg/ha), split between the sowing and at winter wheat jointing growth stage in varying ratios, N1 (0% basal and 100% dressing fertilizer), N2 (30% basal and 70% dressing fertilizer), N3 (50% basal and 50% dressing fertilizer), N4 (70% basal and 30% dressing fertilizer), and N5 (100% basal and 0% dressing fertilizer). Results We found that the N3 treatment significantly increased nitrogen accumulation post-anthesis and nitrogen translocation to grains. In addition, this treatment significantly increased flag leaf free amino acid levels, and nitrate reductase and glutamine synthetase activities, as well as the accumulation rate, active accumulation period, and accumulation of 1000-grain nitrogen. These factors all contributed to high grain nitrogen accumulation. Finally, grain yield increase due to N3 ranging from 5.3% to 15.4% and protein yield from 13.7% to 31.6%. The grain and protein yields were significantly and positively correlated with nitrogen transport parameters, nitrogen metabolic enzyme activity levels, grain nitrogen filling parameters. Conclusions Therefore, the use of split nitrogen fertilizer application at a ratio of 50%:50% basal-topdressing is recommended for supporting high grain protein levels and strong nitrogen translocation, in pursuit of high-quality grain yield.

Effects of Supplement Irrigation and Nitrogen Application Levels on Soil Carbon–Nitrogen Content and Yield of One-Year Double Cropping Maize in Subtropical Region

Inappropriate irrigation conditions and nitrogen application can negatively affect soil carbon–nitrogen content and yield of maize, as well as can lead to underground water pollution and soil degradation. A two year (2018, 2019) field experiment was carried out to determine the effect of irrigation and N, alone and in combination on maize grain yield, grain nitrogen content, soil inorganic N and MBC of one-year double cropping maize (Zea mays L.) in a subtropical region. Split plot design was adopted, with main plots consisting of two water regimes: drip irrigation (drip irrigation to keep soil water content no less than 70% of maximum field capacity) and rainfed (no irrigation during growing period). Split-plot treatments consisted of five nitrogen application levels, including 0 (N0), 150 (N150), 200 (N200), 250 (N250), and 300 kg/ha (N300). The results of two-year field experiment showed that soil irrigation nitrogen interaction had a significant influence on the all measured parameters. In detail, soil NH4+-N and NO3−-N content, total nitrogen (TN), soil organic carbon (SOC) and grain nitrogen contents under the combined treatment of N250 and supplementary irrigation were higher relative to other treatments. Compared with rainfed, maize yield, thousand grains weight (TGW) and harvest index increased by 22.0%, 7.7%, and 15.2% under supplemental irrigation. Yield and TGW N300 were 287 kg/ha and 3.1 g higher than those of N250, and yield and TGW of N250 were 59.4% and 23.1% higher than those of N0, respectively. The yield of spring maize was 24.0% significantly higher than that of autumn maize. Therefore, we suggested that 250 kg/ha nitrogen application fertilizer combined with supplementary irrigation can improve soil fertility and annual maize yield in subtropical one-year double cropping region.

Effect of wheat powdery mildew on grain nitrogen metabolism

Glutamine synthetase (GS) and glutamate synthase (GOGAT) play a central role in plant nitrogen (N) metabolism. In order to study the effect of powdery mildew (Blumeria graminis f. sp. tritici, Bgt) on N metabolism, field experiments were carried out to evaluate GS and GOGAT activity, GS expression and grain protein content (GPC) in susceptible (Xi'nong 979) and resistant (Zhengmai 103) wheat cultivars under three treatments. The three treatments were no inoculation (CK), inoculated once with Bgt (MP) and inoculated nine times with Bgt (HP). For Xi'nong 979, the activities of GS and GOGAT in grains as well as GS activity in flag leaves increased at 10–15 days after anthesis (DAA), and decreased significantly at 15 or 20–30 DAA in HP and MP. However, GS activity in grains decreased from 20 DAA, which was later than that of flag leaves (15 DAA). At the same time, GS expression in grains was up-regulated at early stage, with GS1 at 10 DAA and GS2 at 15 DAA, followed by a continuous down-regulation. This result indicated that GS and GOGAT activity as well as GS expression were inhibited by powdery mildew, indicating that N metabolism in grains was inhibited at 20–30 DAA. The current study also found out that the yield of the susceptible cultivar decreased significantly, while its GPC increased obviously in HP. It was shown that the increase of GPC was not due to the enhancement of N metabolism, but due to the passive increase caused by yield reduction.

Nitrogen Yields and Biological Nitrogen Fixation of Winter Grain Legumes

Grain legumes are valuable sources of protein and contribute to the diversification and sustainability of agricultural systems. Shifting the sowing date from spring to autumn is a strategy to address low yields of spring grain legumes under conditions of climate change. A two-year field experiment was conducted under Pannonian climate conditions in eastern Austria to assess the nitrogen yield and biological N2 fixation of winter peas and winter faba beans compared to their spring forms. The grain nitrogen yields of winter peas and winter faba beans were 1.83-fold and 1.35-fold higher compared to their spring forms, respectively, with a higher value for winter peas. This was mainly due to higher grain yields of winter legumes, as winter faba beans had a 1.06-fold higher grain nitrogen concentration than spring faba bean. Soil mineral nitrate after harvest was similar for all grain legumes, with by 2.85- and 2.92-fold higher values for peas and faba beans than for cereals, respectively. The N2 fixation of winter peas and winter faba beans were 3.90-fold and 2.28-fold higher compared to their spring forms, with winter peas having a 1.60-fold higher N2 fixation than winter faba beans. The negative nitrogen balance of winter peas was smaller than that of winter faba beans as they demonstrated the ability to overcompensate for higher nitrogen removal with grain through higher N2 fixation. The cultivation of winter grain legumes, especially winter peas, can be recommended under Pannonian climate conditions as they achieve high nitrogen yields and high levels of N2 fixation.