Maize (Zea mays L.) responses to salt stress in terms of root anatomy, respiration and antioxidative enzyme activity.

BACKGROUND: Soil salt stress is a problem in the world, which turns into one of the main limiting factors hindering maize production. Salinity significantly affects root physiological processes in maize plants. There are few studies, however, that analyses the response of maize to salt stress in terms of the development of root anatomy and respiration. RESULTS: We found that the leaf relative water content, photosynthetic characteristics, and catalase activity exhibited a significantly decrease of salt stress treatments. However, salt stress treatments caused the superoxide dismutase activity, peroxidase activity, malondialdehyde content, Na+ uptake and translocation rate to be higher than that of control treatments. The detrimental effect of salt stress on YY7 variety was more pronounced than that of JNY658. Under salt stress, the number of root cortical aerenchyma in salt-tolerant JNY658 plants was significantly higher than that of control, as well as a larger cortical cell size and a lower root cortical cell file number, all of which help to maintain higher biomass. The total respiration rate of two varieties exposed to salt stress was lower than that of control treatment, while the alternate oxidative respiration rate was higher, and the root response of JNY658 plants was significant. Under salt stress, the roots net Na+ and K+ efflux rates of two varieties were higher than those of the control treatment, where the strength of net Na+ efflux rate from the roots of JNY658 plants and the net K+ efflux rate from roots of YY7 plants was remarkable. The increase in efflux rates reduced the Na+ toxicity of the root and helped to maintain its ion balance. CONCLUSION: These results demonstrated that salt-tolerant maize varieties incur a relatively low metabolic cost required to establish a higher root cortical aerenchyma, larger cortical cell size and lower root cortical cell file number, significantly reduced the total respiration rate, and that it also increased the alternate oxidative respiration rate, thereby counteracting the detrimental effect of oxidative damage on root respiration of root growth. In addition, Na+ uptake on the root surface decreased, the translocation of Na+ to the rest of the plant was constrained and the level of Na+ accumulation in leaves significantly reduced under salt stress, thus preempting salt-stress induced impediments to the formation of shoot biomass.

Comparative proteomic analysis reveals that exogenous 6-benzyladenine (6-BA) improves the defense system activity of waterlogged summer maize.

BACKGROUND: Exogenous 6-benzyladenine (6-BA) could improve leaf defense system activity. In order to better understand the regulation mechanism of exogenous 6-benzyladenine (6-BA) on waterlogged summer maize, three treatments including control (CK), waterlogging at the third leaf stage for 6 days (V3-6), and application of 100 mg dm- 3 6-BA after waterlogging for 6 days (V3-6-B), were employed using summer maize hybrid DengHai 605 (DH605) as the experimental material. We used a labeling liquid chromatography-based quantitative proteomics approach with tandem mass tags to determine the changes in leaf protein abundance level at the tasseling stage. RESULTS: Waterlogging significantly hindered plant growth and decreased the activities of SOD, POD and CAT. In addition, the activity of LOX was significantly increased after waterlogging. As a result, the content of MDA and H2O2 was significantly increased which incurred serious damages on cell membrane and cellular metabolism of summer maize. And, the leaf emergence rate, plant height and grain yield were significantly decreased by waterlogging. However, application of 6-BA effectively mitigated these adverse effects induced by waterlogging. Compared with V3-6, SOD, POD and CAT activity of V3-6-B were increased by 6.9, 12.4, and 18.5%, LOX were decreased by 13.6%. As a consequence, the contents of MDA and H2O2 in V3-6-B were decreased by 22.1 and 17.2%, respectively, compared to that of V3-6. In addition, the leaf emergence rate, plant height and grain yield were significantly increased by application of 6-BA. Based on proteomics profiling, the proteins involved in protein metabolism, ROS scavenging and fatty acid metabolism were significantly regulated by 6-BA, which suggested that application of 6-BA exaggerated the defensive response of summer maize at proteomic level. CONCLUSIONS: These results demonstrated that 6-BA had contrastive effects on waterlogged summer maize. By regulating key proteins related to ROS scavenging and fatty acid metabolism, 6-BA effectively increased the defense system activity of waterlogged summer maize, then balanced the protein metabolism and improved the plant physiological traits and grain yield.

Effects of plant density on the photosynthetic and chloroplast characteristics of maize under high-yielding conditions.

Plant density has been recognized as a major factor determining the grain yield. The photosynthetic performance changes as the density increases. The main objective of this research was to evaluate responses of photosynthetic performance and chloroplast ultrastructure to planting densities in two summer maize (Zea mays L.) hybrids Denghai661 (DH661) and Nongda108 (ND108). DH661 was planted at densities of 30,000, 45,000, 60,000, 75,000, 90,000, 105,000, 120,000, or 135,000 plants ha-1. ND108 was planted at densities of 30,000, 45,000, 60,000, 75,000, or 90,000 plants ha-1. Research variables included leaf area, grain yield, chlorophyll content, leaf gas exchange parameters, number of chloroplasts, and chloroplast ultrastructure. As plant density increased, chlorophyll a and b content significantly decreased; carotenoids initially decreased and then increased; the net photosynthetic rate during each growth period significantly decreased; the membrane structure of mesophyll cells was gradually damaged; the number of chloroplasts significantly decreased; the external form of chloroplasts shifted from long and oval to elliptical or circular; the number of grana significantly decreased, while the number of grana lamellae increased; grana gradually became hypogenetic and eventually dissolved; plot yield increased; and yield per plant significantly decreased. The yield per plant of DH661 at 135,000 plants ha-1 and that of ND108 at 90,000 plants ha-1 decreased by 65.8 and 42.5%, respectively, compared with those at 30,000 plants ha-1.

Effects of shading on the photosynthetic characteristics and mesophyll cell ultrastructure of summer maize.

A field experiment was conducted to study the effects of shading on the photosynthetic characteristics and mesophyll cell ultrastructure of two summer maize hybrids Denghai605 (DH605) and Zhengdan958 (ZD958). The ambient sunlight treatment was used as control (CK) and shading treatments (40 % of ambient sunlight) were applied at different growth stages from silking (R1) to physiological maturity (R6) (S1), from the sixth leaf stage (V6) to R1 (S2), and from seeding to R6 (S3), respectively. The net photosynthetic rate (P n) was significantly decreased after shading. The greatest reduction of P n was found at S3 treatment, followed by S1 and S2 treatments. P n of S3 was decreased by 59 and 48 % for DH605, and 39 and 43 % for ZD958 at tasseling and milk-ripe stages, respectively, compared to that of CK. Additionally, leaf area index (LAI) and chlorophyll content decreased after shading. In terms of mesophyll cell ultrastructure, chloroplast configuration of mesophyll cells dispersed, and part of chloroplast swelled and became circular. Meanwhile, the major characteristics of chloroplasts showed poorly developed thylakoid structure at the early growth stage, blurry lamellar structure, loose grana, and a large gap between slices and warping granum. Then, plasmolysis occurred in mesophyll cells and the endomembrane system was destroyed, which resulted in the dissolution of cell membrane, karyotheca, mitochondria, and some membrane structures. The damaged mesophyll cell ultrastructure led to the decrease of photosynthetic capacity, and thus resulted in significant yield reduction by 45, 11, and 84 % in S1, S2, and S3 treatments, respectively, compared to that of CK.

Differences of cadmium uptake and accumulation in roots of two maize varieties (Zea mays L.).

Different maize varieties respond differentially to cadmium (Cd) stress. As the first organ in contact with the soil, the response of the root is particularly important. However, the physiological mechanisms that determine the response are not well defined. Here, we compared the differences in Cd-induced related gene expression, ionic homeostasis, and ultrastructural changes in roots of Cd-tolerant maize variety (XR57) and Cd-sensitive maize variety (LY296), and assessed their effects on Cd uptake and accumulation. Our findings indicate that XR57 absorbed a significantly lower Cd than LY296 did, and that the expression levels of genes related to Cd uptake (ZmNRAMP5 and ZmZIP4) and efflux (ZmABCG4) in the root were consistent with the Cd absorption at the physiological levels. Compared with LY296, the lower Cd concentration in the roots of XR57 caused less interference with the ion balance. Transmission electron microscope images revealed that the roots from XR57 exposed to Cd had developed thicker cell walls than LY296. In addition, the large increase ZmABCC1 and ZmABCC2 expression levels in XR57 mediated the appearance of numerous electron-dense granules in the vacuoles present in the roots. As a result, the high Cd tolerance of XR57 is the result of a multi-level response that involves increased resistance to Cd uptake, a stronger capacity for vacuolar regionalization, and the formation of thicker cell walls. These findings may provide a theoretical basis for maize cultivation in Cd-contaminated areas.

[Effects of seed grading on population regularity degree and yield of summer maize]. / 种子分级对夏玉米群体整齐度和产量的影响.

Grading seeds based on grain size is an effective measure to improve population regularity degree and increase the yield of summer maize. Taking Denghai 605 as the experimental material, we set up a field experiment with treatments based on grain size: large seeds (L), medium-round seeds (MR), medium-flat seeds (MF), medium-round and medium-flat mixed seeds (MRF), and small seeds (S), with no-grading seeds as control (CK). We investigated seedling emergence rate, population regularity degree (including height, ear height and stem diameter), seedling sturdiness index, photosynthetic characteristics, dry matter accumulation and distribution characteristics, and yield. The results showed that the emergence rate followed an order of L>MR>MRF>MF>CK>S, with that of L treatment differed little from MR, MF and MRF treatments, but being significantly higher than S and CK treatments. Plant height and stem diameter population regularity degree of MRF treatment before seven-leaf stage was not different from those of L, MR, MF and S treatments, but significantly higher than those of CK. At the tasseling stage, all treatments had higher population regularity degree of plant height than other stages. Ear height population regularity degree of L, MR, MF, MRF, and S increased by 11.1%, 10.3%, 9.5%, 7.1%, and 6.4% compared with CK, respectively. The seedling sturdiness index of MRF treatment increased by 36.7% compared with S treatment, but was not significantly different from L treatment. The leaf area index of the L and MRF treatments was significantly higher than that of CK, and both had higher population photosynthetic properties. The population dry matter accumulation showed a pattern as L>MR>MRF>MF>CK>S. There was no significant difference among L, MR, and MRF treatments, but that in L being obviously higher than MF, CK, and S treatments. After seed grading, the number of harvested ears of the L and MRF treatments increased significantly, and the yield were shown as L>MR>MRF>MF>CK>S. There was no difference between the yield of MRF, MR and MF treatments. In conclusion, the performance of L treatment was improved but the number was small. Considering the grading cost and yield, the MRF treatment can save the seed amounts of sowing, realize mechanized sowing and precision sowing.

Yield of summer maize hybrids with different growth duration determined by light and temperature resource use efficiency from silking to physiological maturity stage.

In order to explore the physiological mechanism of different yield of summer maize (Zea mays L.) hybrids with different growth duration, a field experiment was conducted to study the growth stage, leaf photosynthetic characteristics, dry matter accumulation (DMA), transport and distribution characteristics and yield of the early maturity hybrid Denghai 518 (DH518) and the mid-late maturity hybrid Denghai 605 (DH605) from 2017 to 2021. The results showed that the yield of DH605 was significantly higher than that of DH518. The growth period of DH518 was 7-10 days shorter and the days of the growth stage of the sowing-silking stage (R1) were 5-6 days shorter compared to that of DH605. The contribution to grain dry matter by leaf and stalk dry matter remobilization (DMRC) of DH518 was significantly higher than that of DH605. There was a significant negative correlation between pre-silking growth days and harvest index (HI). The 13C distribution to grains of DH518 was significantly higher than that of DH605, and the HI and the corresponding contribution of HI to yield was also higher than that of DH605. The light and temperature resource use efficiency from silking to physiological maturity stage of DH605 was significantly higher than that of DH518. The yield per GDD of DH605 increased by 7.25% than that of DH518. At post-silking, the duration of higher leaf area index (DLAI) (>56 days) and active photosynthesis duration (APD) (>50 days) of DH605 were longer compared with that of DH518, and the average plant growth rate was 7.15% higher than that of DH518, which significantly increased the DMA of DH605. Therefore, the significant reduction of DH518 yield compared with DH605 was not due to the shortening of the growth stage of sowing-R1, but the lower light and temperature resource use efficiency from silking to physiological maturity stage.

Influences of split application and nitrification inhibitor on nitrogen losses, grain yield, and net income for summer maize production.

The application of nitrogen (N) fertilizer combined with nitrification inhibitor is considered to be one of the effective strategies to improve N efficiency and reduce N loss. While the chemical and physical properties of nitrapyrin (CP) in fertilizers have been evaluated to increase N efficiency, a lack of comprehensive evaluation of the effects of adding CP on summer maize yield, environmental benefits and economic income under different fertilization methods. In this study, two fertilization methods were used: split-N application and one-time basal N fertilizer before sowing. The comprehensive effects of N fertilizer with CP on N loss (NH3 volatilization, NO3 - leaching, and N2O emissions), N efficiency, yield and profit under two N application methods were explored. Results showed that under the two N application methods, N fertilizer with CP treatment increased the N efficiency and yield (+3.4%∼+5.7%), significantly reduced the soil NO3 --N content and N2O emissions, while increased NH3 volatilization. Especially, the increase amplitude of NH3 was much less than the decrease amplitude of N2O induced by adding CP. Although split-N application could achieve higher yield and N efficiency, N2O emissions and NH3 volatilization also increased. However, the T1 + N (one-time basal N fertilizer before sowing mixed with CP) achieved the same yield level as T2 treatment (split-N application). Taking agronomic, economic and environmental benefits into consideration, one-time basal N fertilizer before sowing mixed with CP could ensure the target yield, increase economic benefits, maintain soil N content, and reduce N losses. Therefore, optimizing N management is essential to the sustainable development of agriculture.

Nitrapyrin Mitigates Nitrous Oxide Emissions, and Improves Maize Yield and Nitrogen Efficiency under Waterlogged Field.

In order to explore the effects of nitrapyrin (N-Serve) application on greenhouse gas emission and nitrogen (N) leaching of a waterlogged maize (Zea mays L.) field, we investigated the effects of applying nitrapyrin on soil ammonium (NH4+-N) and nitrate nitrogen (NO3--N) content, nitrous oxide (N2O) fluxes, and the warming potential (GWPN2O) in a waterlogged maize field. The design included three treatments: waterlogging treatment with only urea application (V-3WL), waterlogging treatment with urea and nitrapyrin application (V-3WL+N), and no waterlogging treatment applying only urea (CK). Our results revealed that waterlogging led to the increase of nitrate concentrations across the soil profile, thus potentially increasing N leaching and decreasing N use efficiency. The accumulated N2O emissions increased significantly in waterlogged plots compared to control plots, and maximum N2O emission fluxes occurred during the process of soil drying after waterlogging; this resulted in an increase in GWPN2O and N2O greenhouse gas intensity (GHGIN2O) by 299% and 504%, respectively, compared to those of CK. However, nitrapyrin application was able to reduce N2O emissions. Nitrapyrin application was also good for decreasing GWPN2O and GHGIN2O by 34% and 50%, respectively, compared to V-3WL. In addition, nitrapyrin application was conducive to reduce N leaching and improve N use efficiency, resulting in a yield increase by 34%, compared to that of V-3WL. The application of nitrapyrin helped to mitigate agriculture-source greenhouse effects and N leaching induced by waterlogging, and was a high N-efficient fertilizer method for a waterlogged field.

Spraying Ethephon Effectively Increased Canopy Light Transmittance of Densely Planted Summer Maize, Thus Achieving Synergistic Improvement in Stalk Lodging Resistance and Grain Yield.

Increasing planting density is an effective way to improve maize yield, but high plant populations often cause a lodging problem. This experiment was conducted to investigate the effect of increasing planting density on stalk lodging resistance and grain yield, and to explore the effects on stalk and yield properties of spraying ethephon in densely planted summer maize. The summer maize hybrid, Xundan20 (XD20), was used as experimental material. It was grown by spraying water (CK) or ethephon (E) at BBCH (BASF, Bayer, Ciba-Geigy and Hoechst) 17 under three different planting densities of 60,000 plants ha-1 (L), 75,000 plants ha-1 (M) and 90,000 plants ha-1 (H) in order to explore the possibility of synergistic improvement in stalk lodging resistance and grain yield. The results from this experiment suggested that the gravity center height of densely planted summer maize was significantly increased, the stem diameter, area and number of vascular bundles were significantly decreased and the dry weight per unit internode was significantly decreased, thereby weakening the stalk rind penetration strength and bending performance, resulting in a significant increase in lodging percentage. The ear height was significantly decreased and the SPAD (soil and plant analysis development) and canopy light transmittance were increased after spraying ethephon; then, the internode dry weight per unit length was increased and the stalk rind penetration strength and bending performance were enhanced so as to significantly reduce the lodging percentage and increase the grain yield. The correlation analysis further showed that lodging percentage was significantly negatively correlated with stem diameter, area and number of vascular bundles and stalk bending performance, but there were no strong relationships with grain yield. This suggested that the synergistic improvement in stalk lodging resistance and grain yield was not contradictory. Under the experiment conditions, the effect of spraying ethephon was most significant when the planting density was 90,000 plants ha-1. At the time, the lodging percentage and grain yield were 12.2% and 11,137.5 kg ha-1, which were decreased by 44.6% and increased by 8.0% compared with the control treatment. Scientific chemical regulation could significantly improve the stalk lodging resistance and grain yield of densely planted summer maize.

6-Benzyladenine increasing subsequent waterlogging-induced waterlogging tolerance of summer maize by increasing hormone signal transduction.

Summer maize is frequently subjected to waterlogging damage because of increased and variable rainfall during the growing season. The application of 6-benzyladenine (6-BA) can effectively mitigate the waterlogging effects on plant growth and increase the grain yield of waterlogged summer maize. However, the mechanisms underlying this process and the involvement of 6-BA in relevant signal transduction pathways remain unclear. In this study, we explored the effects of 6-BA on waterlogged summer maize using a phosphoproteomic technique to better understand the mechanism by which summer maize growth improves following waterlogging. Application of 6-BA inhibited the waterlogging-induced increase in abscisic acid (ABA) content and increased the phosphorylation levels of proteins involved in ABA signaling; accordingly, stomatal responsiveness to exogenous ABA increased. In addition, the application of 6-BA had a long-term effect on signal transduction pathways and contributed to rapid responses to subsequent stresses. Plants primed with 6-BA accumulated more ethylene and jasmonic acid in response to subsequent waterlogging; accordingly, leaf SPAD, antioxidase activity, and root traits improved by 6-BA priming. These results suggest that the effects of 6-BA on hormone signal transduction pathways are anamnestic, which enables plants to show faster or stronger defense responses to stress.

Exogenous 6-Benzyladenine Improved the Ear Differentiation of Waterlogged Summer Maize by Regulating the Metabolism of Hormone and Sugar.

Waterlogging (W-B) is a major abiotic stress during the growth cycle of maize production in Huang-huai-hai plain of China, threatening food security. A wide range of studies suggests that the application of 6-benzyladenine (6-BA) can mitigate the W-B effects on crops. However, the mechanisms underlying this process remain unclear. In this study, the application of 6-BA that effectively increased the yield of summer maize was confirmed to be related to the hormone and sugar metabolism. At the florets differentiation stage, application of 6-BA increased the content of trans-zeatin (TZ, + 59.3%) and salicylic acid (SA, + 285.5%) of ears to induce the activity of invertase, thus establishing sink strength. During the phase of sexual organ formation, the TZ content of ear leaves, spike nodes, and ears was increased by 24.2, 64.2, and 46.1%, respectively, in W-B treatment, compared with that of W. Accordingly, the sugar metabolism of summer maize was also improved. Therefore, the structure of the spike node was improved, promoting the translocation of carbon assimilations toward the ears and the development of ears and filaments. Thus the number of fertilized florets, grain number, and yield were increased by the application of 6-BA.

Long-term integrated soil-crop management improves soil microbial community structure to reduce GHG emission and increase yield.

Integrated soil-crop management (ISCM) has been shown as an effective strategy to increase efficiency and yield while its soil microbial community structure and function remain unclear. We evaluated changes in soil physicochemical factors, bacterial community structure responses, and the contributions of soil properties and bacterial communities to summer maize-winter wheat yield and GHG emissions through an ISCM experiment [T1 (local smallholder farmers practice system), T2 (improved management system), T3 (high-yield production system), and T4 (optimized management system)], which could provide scientific guidance for sustainable development of soil in summer maize-winter wheat rotation system. The results showed that the optimized ISCM could improve the soil quality, which significantly changed the soil bacterial community structure to reduce GHG emissions and increase yield. The co-occurrence network density of T3 was increased significantly. The Acidobacteria (class) and OM190 (class) were enriched in T2 and T4. The Frankiales (order) and Gaiellales (order) were enriched in T3. However, the changes in different crop growth stages were different. At the wheat jointing stage and maize mature stage, T4 could enhance carbon-related functional groups, such as aromatic hydrocarbon degradation and hydrocarbon degradation, to increase the soil organic carbon content. And at the maize tasseling stage, T4 could enhance nitrogen-related functional groups. And soil bacteria structure and function indirectly affected annual yield and GHG emission. T2 and T4 exhibited a similar soil microbial community. However, the yield and nitrogen use efficiency of T2 were reduced compared to those of T4. The yield of T3 was the highest, but the GHG emission increased and soil pH and nitrogen use efficiency decreased significantly. Therefore, T4 was a suitable management system to improve soil quality and soil bacterial community structure and function to decrease GHG emissions and increase the yield of the summer maize-winter wheat rotation system.

Effects of hydrogen peroxide priming on yield, photosynthetic capacity and chlorophyll fluorescence of waterlogged summer maize.

Extreme rainfall events during the summer maize growth and development periods, which have induced losses in summer maize production. There was a completely randomized block experiment being designed with four treatments: waterlogging for 6 days at the V3 stage (C-W), H2O2-priming + non-waterlogging (H-CK), H2O2-priming + waterlogging for 6 days at the V3 stage (H-W) and control (C-CK). This study investigated the effects of H2O2 priming on yield and photosynthetic parameters of (Zea mays. L) summer maize hybrid DengHai605 (DH605) by measuring the leaf area index (LAI), soil and plant analyzer development (SPAD) value, stomatal morphology, gas exchange parameters, and chlorophyll fluorescence parameters. The results showed that the net photosynthetic rate (Pn) was decreased after waterlogging through the stomatal limitation of CO2 supply and reduction of PSII photochemical efficiency, which led to the decrease in dry matter accumulation and grain yield. H2O2 priming increased the number of opening stomas, the stomatal length, and width, thus increasing Ci by 12.1%, which enhanced the Pn by 37.5%. Additionally, H2O2 priming could improve the energy of dark reaction carbohydrates by increasing the light energy absorption and utilization, alleviating the function of PSII reaction centers, protecting the PSII receptor and donor side, and the electron transport chain. The φEo, φPo, φRo, and Ψo of H-W were increased by 89.9%, 16.2%, 55.4%, and 63.9% respectively, and the φDo was decreased by 23.5%, compared with C-W. Therefore, H2O2 priming significantly enhanced the PSII photochemical efficiency, and increased the CO2 supply in dark reactions to promote carbon assimilation, alleviating the waterlogging-induced damage to maize plant growth and grain yield.

Responses of nitrogen efficiency and antioxidant system of summer maize to waterlogging stress under different tillage.

Waterlogging was one of the main abiotic stresses affecting maize yield and growth in the North China Plain, while ridge tillage effectually improved soil environment, enhanced crop stress resistance to waterlogging, and increased grain yield of waterlogged maize. In order to explore the responses of nitrogen (N) efficiency and antioxidant system of summer maize to waterlogging stress under different tillage, a field experiment was conducted to explore N use efficiency, leaf activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and malondialdehyde (MDA) content of waterlogged maize Denghai 605 (DH605) and Zhengdan 958 (ZD958) under different tillage system (ridge planting and flat planting). Our results showed that ridge tillage was beneficial to ameliorate waterlogging damages on antioxidant system by increasing SOD, POD, and CAT activities, and decreasing MDA content. Moreover, ridge tillage significantly increased N efficiency of waterlogged maize. N translocation amount (NTA), N translocation efficiency (NTE), N contribution proportion (NCP), N harvest index (NHI), and N use efficiency (NUE) of waterlogging treatment under ridge planting system (W-V3+R) for DH605 was increased by 108%, 69%, 60%, 8% and 16%, while ZD958 increased by 248%, 132%, 146%, 13% and 16%, respectively, compared to those of waterlogging treatment under flat planting system (W-V3). Ultimately, ridge tillage led to a significant yield improvement by 39% and 50% for DH605 and ZD958, respectively, compared to that of W-V3. In conclusion, ridge tillage was conducive to retard leaf aging, and enhance nitrogen efficiency, thereby resulting in a yield improvement of waterlogged summer maize.

Effects of Urea-Ammonium Nitrate Solution on Yield, N2O Emission, and Nitrogen Efficiency of Summer Maize Under Integration of Water and Fertilizer.

In order to clarify the effects of urea-ammonium nitrate solution (UAN) on the yield, nitrogen-use efficiency (NUE), and N2O emissions of summer maize under the condition of water and fertilizer integration, different types of nitrogen fertilizer were selected, namely, ordinary urea (urea) and UAN. Our results showed that the application of UAN was beneficial to improve the dry matter accumulation and the distribution of summer maize. Compared with urea treatment, the total nitrogen accumulation of UAN treatment was increased by 15.8%, and the harvest index was increased by 5.5%. The partial productivity, agronomic use efficiency, and recovery rate of nitrogen for UAN treatment were also increased by 9.1, 19.8, and 31.2%, respectively, compared to those of urea treatment. The soil nitrogen dependence rate treated with UAN was significantly decreased by 13.6%, compared to that of urea treatment. In addition, UAN was beneficial to reduce N2O emissions. The N2O warming potential (GWPN2O) and N2O greenhouse gas intensity (GHGIN2O) of urea treatment were 39.3 and 52.4% higher, compared to those of UAN treatment. The improvement of dry matter accumulation and distribution and nitrogen efficiency for UAN treatment were beneficial to increase the grain yield by 9.1%, compared to that of urea treatment. In conclusion, under the fertigation, the application of UAN favors higher yield and nitrogen uptake, with less soil nitrogen residue, higher NUE, and better environmental effect.

Endogenous Hormones Inhibit Differentiation of Young Ears in Maize (Zea mays L.) Under Heat Stress.

Global warming frequently leads to extreme temperatures, which pose a serious threat to the growth, development, and yield formation of crops such as maize. This study aimed to deeply explore the molecular mechanisms of young ear development under heat stress. We selected the heat-tolerant maize variety Zhengdan 958 (T) and heat-sensitive maize variety Xianyu 335 (S), and subjected them to heat stress in the V9 (9th leaf), V12 (12th leaf), and VT (tasseling) growth stages. We combined analysis of the maize phenotype with omics technology and physiological indicators to compare the differences in young ear morphology, total number of florets, floret fertilization rate, grain abortion rate, number of grains, and main metabolic pathways between plants subjected to heat stress and those left to develop normally. The results showed that after heat stress, the length and diameter of young ears, total number of florets, floret fertilization rate, and number of grains all decreased significantly, whereas the length of the undeveloped part at the top of the ear and grain abortion rate increased significantly. In addition, the differentially expressed genes (DEGs) in young ears were significantly enriched in the hormone signaling pathways. The endogenous hormone content in young ears exhibited different changes: zeatin (ZT) and zeatin riboside (ZR) decreased significantly, but gibberellin acid3 (GA3), gibberellin acid4 (GA4), and abscisic acid (ABA) increased significantly, in ears subjected to heat stress. In the heat-tolerant maize variety, the salicylic acid (SA), and jasmonic acid (JA) content in the vegetative growth stage also increased in ears subjected to heat stress, whereas the opposite effect was observed for the heat-sensitive variety. The changes in endogenous hormone content of young ears that were subjected to heat stress significantly affected ear development, resulting in a reduction in the number of differentiated florets, fertilized florets and grains, which ultimately reduced the maize yield.

[Effects of spraying desiccant on dehydration characteristics and grain quality of summer maize hybrids differing in maturity]. / 喷施脱水剂对不同熟期夏玉米脱水特性和籽粒品质的影响.

Water content of summer maize hybrids grown in China is too high at harvesting stage, which limits the development of grain mechanical harvesting technology. Spraying the desiccant can regulate physiological process of crop grain filling and reduce water content at harvest. We explored the effects of spraying the desiccant on the dehydration process, grain moisture, and grain quality of summer maize hybrids differing in maturity. Spraying the desiccants reduced dry matter accumulation in different organs of maize, with strongest reduction of middle-late maturity hybrids. Dry matter transfer to the grains of the plants and the harvest index was improved, but with no changes of grain quality. The dehydration rate of grains was positively correlated with the rate of dehydration in diffe-rent organs. The dehydration rate of grains after spraying the desiccants was significantly positively correlated with the rate of dehydration of stems and sheaths. With no negative effects on yield, spraying the desiccant increased the total dehydration rate, shortened the time from flowering to physiological maturity, and increased the time from physiological maturity to harvest, which was beneficial to the further reduction of grain moisture in the later stage. The possibility of grain mechanical harvesting was increased. The economic benefits of spraying the desiccants on mechanical grain harvest of summer maize hybrids differing in maturity were not significantly different from those of ear mechanical harvesting. The economic benefits of middle-late maturity hybrids were higher than those of early maturity hybrids. Spraying desiccant may improve the possibility of grain mechanical harvesting.

[Effects of phytase Q9 on the yield and senescence characteristics of summer maize shaded in the field]. / æ¤é ¶Q9对大田遮阴夏玉米产量和衰老特性的调控作用.

Light shortage in the canopy of summer maize resulted from the decrease of solar radiation and the increase of planting density in Huanghuaihai region could reduce maize yield. In order to explore the effects of phytase Q9 on leaf senescence characteristics of summer maize, three sha-ding treatments with summer maize hybrid 'Denghai 605' (DH605) were conducted, including shading at flowering to maturity stage (S1), shading at ear stage (S2), and shading at whole growth stage (S3) with natural lighting in the field as control (CK). Chemical control reagent phytase Q9 was used to regulate the shading treatments (the original solution was diluted by 100 times) and the CK exogenously, namely shading at flowering to maturity stage-phytase Q9 (S1Q), shading at ear stage-phytase Q9 (S2Q), and shading at whole growth stage-phytase Q9 (S3Q), and natural lighting-phytase Q9 (CKQ), with spraying water at the same stage as the control. The results showed that leaf area index (LAI), soil-plant analysis development (SPAD) value and net photosynthetic rate of summer maize was significantly reduced by shading, which led to decreases of yield. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in ear-leaf decreased. The content of malondialdehyde (MDA) and free proline increased, and that of soluble protein decreased. The spraying phytase Q9 significantly increased LAI, SPAD and net photosynthetic rate in S3Q and S2Q. MDA and free proline content in S3Q, S2Q, and S1Q were significantly decreased, and soluble protein content and POD activity was significantly increased. SOD and CAT activities in S2Q and S3Q were significantly increased. The yield of S3Q, S2Q and S1Q were 19%, 8% and 7% higher than that of S3, S2 and S1 respectively. There was no significant difference between CKQ and CK. In conclusion, phytase Q9 could effectively alleviate the negative impact of low light on yield formation of summer maize, and increase grain yield by improving photosynthetic capacity of leaves and delaying leaf senescence.

Effects of residue management strategies on greenhouse gases and yield under double cropping of winter wheat and summer maize.

The North China Plain (NCP) is typically cropped using a winter wheat-summer maize double cropping system, which has huge potential for straw production. The region also experiences atmospheric pollution caused by straw burning, which has become an important contributor to global warming. The goals of this experiment were to resolve the conflict between soil fertility and greenhouse gas emission when using straw return to the field and to identify the best balance between environmental protection and agricultural production. A randomized block design with three replicates was used. The design included three treatments based on the return of all winter wheat stalks to the field: (1) all summer maize stalks were pulverized mechanically and returned to the field (SR); (2) half of the summer maize stalks were pulverized mechanically and returned to the field (1/2 SR); and (3) all summer maize stalks were fully removed (control: CK). This long-term test was performed for 6 years. Straw returned to the field significantly increased greenhouse gas emissions. The cumulative CO2 emissions were higher by 32% under SR and by 17% under 1/2 SR compared with CK. The cumulative N2O emissions were higher by 28% under SR and 15% under 1/2 SR compared with CK. The greenhouse gas efflux increased with increased amounts of straw returned to the field. Compared with SR, 1/2 SR significantly reduced greenhouse gas emissions, while still ensuring sustainable soil fertility. Additionally, our research showed that the upper part of the corn stalk is better for generating biomass energy than the lower part. This study provides a theoretical basis for using the upper stalk for bioenergy and the lower stalk for direct return to the field for fertilization.