Knowledge of the maize pollen development stages at which high temperature (HT) stress leads to male sterility and yield loss would support targeted breeding strategies. In a cross between Zhengdan 958 (HT-tolerant) and Xianyu 335 (HT-sensitive) the contributions of maize traits to effective grain number (EGN) loss under HT stress were measured during pollen development stages, with loss increasing with the approach of flowering. Traits including pollen number per anther, total tassel spikelets, and pollen germination and shedding were the strongest contributors at various stages. The stage-specific vulnerabilities of maize tassels to HT stress suggest increasing pollen production before the tetrad stage and increasing pollen fertility and shedding during the microspore development stage. In the short term, increasing pollen developmental quality offers the greatest potential for reducing HT-caused EGN loss.
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Based on a long-term positioning test platform, the differences of annual ammonia volatilization loss of soil nitrogen in wheat-maize rotation system under different fertilization treatments were compared, aimed to provide a theoretical basis for reducing nitrogen volatilization loss and improving fertilizer use efficiency.
From 2019 to 2021, the winter wheat variety Shimai 15 and summer maize variety Zhengdan 958 were used as experimental materials in this study. With no nitrogen fertilizer applied as the control (CK), the two kinds of nitrogen fertilizer types (organic manure: M; urea: U) and two N application rates (380 kg N·hm-2: M1, U1, U2M2, and 190 kg N·hm-2: U2, M2) were set, and the distribution of N fertilizer between two crops was 47.4% for wheat and 52.6% for maize. The venting method was used to compare the differences in annual ammonia volatilization rate, cumulative loss, grain yield, and nitrogen use efficiency in a wheat-maize rotation system under different fertilization treatments.
Different fertilization treatments significantly affected soil ammonia volatilization in the two growing seasons. The soil ammonia volatilization mainly occurred 0-7 days after fertilization during the annual year in the wheat and maize crops, and the difference between the treatments gradually became smaller. The annual ammonia volatilization loss ranged from 8.6 to 79.4 kg N·hm-2. The highest ammonia volatilization loss was 79.4 kg N·hm-2 under U1 treatment, which was 18.5%, 111.7%, 162.3%, 20.5%, and 825.7% higher than that under U2, U2M2, M1, M2, and CK, respectively. The high nitrogen application rate increased soil ammonia volatilization loss, and the loss of inorganic nitrogen fertilizers was greater than that of organic fertilizers. The annual nitrogen fertilizer ammonia volatilization loss rate under U2M2, M1, and M2 treatment was 80.9%, 40.8%, and 61.3% lower than that under U1, respectively. It was indicated that the organic and inorganic fertilizers combined application or single organic fertilizers application could significantly reduce ammonia volatilization losses. The annual grain yield under U2M2 treatment was the highest, which was 24 621.8 kg·hm-2, and was 10.1%, 24.7%, 11.7%, and 32.7% higher than that under U1, U2, M1, and M2, respectively. The annual nitrogen utilization efficiency under U2M2 treatment was 52.6%, which was 11.3%, 4.1%, 13.4%, and 10.7% higher than that under U1, U2, M1, and M2, respectively. U2M2 treatment reduced the ammonia volatilization loss and simultaneously increased the grain yield and nitrogen use efficiency, which was an ideal fertilization strategy for the annual rotation of winter wheat and maize.
The application of organic fertilizer could significantly reduce the annual ammonia volatilization loss of the wheat-maize rotation system, and increase the annual grain yield and nitrogen fertilizer use efficiency. Considering the source of organic fertilizer and the convenience of application, the organic and inorganic fertilizers combined application could be used as the main fertilization method to reduce the loss of ammonia volatilization and to improve the efficiency of nitrogen fertilizer use efficiency in wheat-maize rotation production system.
This study aimed to explore the underlying reasons for the reduction of maize photosynthesis under the high temperature and drought combined stress, so as to provide theoretical basis for alleviating the combined stress of high temperature and drought.
Maize cultivar “Denghai 605” was selected as the experimental material for this experiment. Two temperature levels were set, namely normal temperature control (30 ℃/22 ℃ for day (8:00-18:00)/ night (18:00- 8:00 the next day)) and high temperature treatment (38 ℃/28 ℃ for day/night). The two water conditions were normal water supply control (soil water content was 70%-80% of field capacity) and drought treatment (soil water content was set to 50%-60% of field capacity). There were four treatments in the experiment, including control (CK), high temperature stress (H), drought stress (D), high temperature and drought combined stress (HD), and the treatment began at VT stage (VT). The changes in leaf gas exchange parameters, photosystem Ⅱ (PSII) performance, key photosynthetic enzyme activity, plant biomass, and grain yield under different stress treatments were analyzed.
High temperature, drought and combined stress all led to the increase of chlorophyll fluorescence parameters, the ratio of a variable fluorescence FK to F0-FJ amplitude (WK) and variable fluorescence FJ to F0-FJ amplitude (VJ), and damaged the donor side and acceptor side of PSII. Compared with the control, PSII maximum quantum yield for primary photochemistry (φP0), the probability of captured excitons transferring electrons to other electron acceptors in the electron transfer chain beyond QA (Ψ0), quantum yield for electron transport (φE0), quantum yield of energy dissipation (φD0), quantum yield for reduction of the end electron acceptors at the PSI acceptor side (φR0), and performance index based on absorption of light energy (PIABS) were significantly decreased, and the absorption and transfer of light energy were inhibited; absorbed photon flux per active PSII (ABS/RC), trapped energy flux per active PSII (TR0/RC) and dissipated energy flux per active PSII (DI0/RC) increased significantly, but the electron flux from QA‒ to the PQ pool per active PSII (ET0/RC) decreased significantly, which affected the energy distribution of reaction centers, reduced the number of PSII active reaction centers, and inhibited the performance of PSII. Combined stress could aggravate the inhibition of PSII performance by damaging the donor side, the acceptor side and the active reaction center. At the same time, the activities of ribose 1, 5-diphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPCase) decreased, which inhibited photosynthetic carbon assimilation. High temperature, drought, and combined stress reduced the net photosynthetic rate by reducing the performance of PSII and the activity of key photosynthetic enzymes. Compared with the control, the net photosynthetic rate of VT+5 d was reduced by 14.6%, 31.4%, and 39.9%, respectively. The decrease in photosynthetic rate inhibited the accumulation of biomass and its transport to grains. Under high temperature, drought, and combined stress, the grain yield decreased by 80.3%, 27.1%, and 84.0% than that under control, respectively.
In summary, the combined stress of high temperature and drought mainly reduced net photosynthetic rate, hindered biomass, and reduced grain yield by inhibiting leaf PSII performance. The impact of combined stress on PSII performance and grain yield was greater than that of single stress under high temperature and drought.
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Planting maize at high densities leads to early leaf senescence, and the resulting reduction in the number of lower leaves affects the plant’s root function and lowers its grain yield. However, the nature of the process by which lower leaf senescence affects biomass accumulation and grain yield formation in maize is not clear. This study aimed to shed light on how these factors are related by investigating the effects of the plant growth regulator 6-benzyladenine (6-BA) on the senescence of lower leaves of maize plants. In two maize cultivars planted at densities of 67,500 (low density, LD) and 90,000 (high density, HD) plants ha−1, plants treated with 6-BA maintained a high green leaf area index (LAI) longer than control (CK) plants, enabling them to maintain a higher photosynthetic rate for a longer period of time and produce more biomass before reaching physiological maturity. Spraying the lower leaves of maize plants with a 6-BA solution increased the distribution of 13C-photosynthates to their roots, lower leaves and bracts, a result that can be ascribed to a decreased retention of 13C-photosynthates in the stem and grain. In both seasons of the experiment, maize plants treated with 6-BA accumulated more N in grain and maintained a higher N content in roots and leaves, especially in lower leaves, than CK. Increased C assimilation in the lower leaves may explain why N uptake in plants subjected to the 6-BA treatment exceeded that in CK plants and why both photosynthesis rate and dry matter accumulation were maintained throughout grain filling. Our results suggest that a suitable distribution of C and N in leaves post-silking may maintain plant root function, increase N use efficiency, maximize the duration of high LAI, and increase grain yield.
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