【Objective】 Global seasonal high temperature and drought have become the main limiting factors affecting crop growth and development as well as yield formation. Based on artificial simulation of the climate characteristics of periodic high temperature and drought stress, the effects of high temperature stress, drought stress and the combined stress of high temperature and drought during the flowering stage on morphological development and physiological characteristics of tassel and yield formation of summer maize were explored in this study. 【Method】 The experiment was conducted by pot-experiment in the greenhouse with intelligent control system for two years. Zhengdan 958 (ZD958) and Huanong 138 (HN138) were used as the experimental materials. The four treatments of control (CK), flowering high-temperature stress treatment (T), flowering drought stress treatment (D) and flowering high-temperature-drought combined stress treatment (TD) were set up to study the tassel morphology, anther and pollen structure, pollen viability, tassel antioxidant index and yield of summer maize in response to high temperature and drought during flowering stage. 【Result】 High temperature, drought and combined stress resulted in significant reduction in the tassel branch number, tassel central branch spikelet number and tassel branch spikelet density in maize, and these three parameters of T treatment were 17.31%, 15.70% and 13.56% lower than that under CK, respectively; D and TD treatments were 33.85%, 24.87%, 27.08% and 45.59%, 32.02%, 26.00% lower than CK, respectively. Drought and combined stress significantly shortened tassel central branch length by 23.64% and 27.51%, respectively, compared with CK. High temperature stress and drought stress at flowering stage led to anther shrinkage and deformation, loose arrangement of tapetum cells, and reticular protrusion on pollen grain surface. Combined stress aggravated anther shrinkage and deformation, broken of tapetum cells. And the septal vascular bundles became thinner, the number decreased, the reticular protrusion of pollen grains was more obvious, and the germination holes were invaginated under combined stress. High temperature, drought and combined stress significantly reduced the dispersed amount of pollen in tassel, and the dispersed amount of pollen under T, D and TD treatments was 22.18%, 54.75% and 67.28% less than CK, respectively. The date of maximum dispersed amount of pollen was earlier than that under CK. T, D and TD treatments significantly reduced the proportion of highly vigorous pollen compared with CK. T treatment increased the activities of SOD and POD enzymes in the tassel by 21.91% and 32.50%, respectively, compared with CK; While those under D and TD treatment increased by 24.95% (SOD), 53.37% (POD) and 17.12% (SOD), 67.24% (POD), respectively, compared with CK. The MDA content in the tassel under T, D and TD treatment increased by 44.18%, 64.24%, and 79.12%, respectively, compared with CK; The $\mathop{{O}}_{2}^{{\mathop{}_{\ •}^{-}}}$ content increased by 22.55%, 51.65%, 72.29%, respectively, compared with CK. High temperature, drought and combined stress reduced maize yield and grain number per row by 18.05%, 34.58%, 46.24% and 24.58%, 41.80%, 52.99%, respectively, compared with CK. Under stress treatment, the tassel branch number, the tassel central branch spikelet number and the tassel branch spikelet density of HN138 were decreased by 27.00% and 17.28%, respectively, compared with ZD958; The distortion degree of anther and pollen structure of HN138 was higher than that of ZD958, and the increase of antioxidant enzyme activity was less than that of ZD958, but MDA and O2 ·-content were 13.07% and 20.29% higher than that of ZD958. HN138 was more sensitive to high temperature, drought and combined stress between two cultivars. 【Conclusion】 The results showed that high temperature, drought and combined stress significantly inhibited the growth and development of tassel, led to the distorted morphological structure of anther and pollen, reduced the dispersed amount of pollen, decreased the activity of antioxidant enzymes, and inhibited the normally pollination and fructification, thus resulting in the decreased kernel number and grain yield. The effect of combined stress of high temperature and drought on tassel was greater than that of single stress, but the response of different varieties to high temperature and drought was different.
【Objective】 With the global climate change, the effects of elevated temperature on maize production system are increasingly complex. Lodging resistance plays an important role on the completely mechanized maize production system in present and the future. Thus, the studying on the characteristics of maize stem and lodging resistance responding to gradient warming during the whole season could provide the theoretical and practical basis to the adaptive cultivation approach in response to climate change in the future. 【Method】 Zhengdan 958 (ZD958) and Xianyu 335 (XY335) were tested as materials. Three temperature gradient of CK, CK+2℃, CK+4℃ were conducted in the greenhouse to study the effects of gradient warming on stem growth and development, stem mechanics characters, lodging resistance characters and grain yield. 【Result】 The results showed that with increasing temperature, plant height, ear height, the third internode length, stem length under the ear and above the ear were significantly higher than that of CK; CK+2℃ increased on average by 10.80%, 37.29%, 16.87%, 17.11% and 17.78%, respectively, compared to CK; CK+4℃ increased on average by 20.82%, 54.17%, 37.11%, 28.48% and 35.84%, respectively, compared to CK. Temperature increment significantly increased the ear location coefficient and stem diameter coefficient. Compared with CK+2℃ and CK, the stem diameter coefficient of CK+4℃ was increased by 15.92% and 58.99% on average, respectively. Temperature increment significantly decreased the number and area of vascular bundles of stems. Compared with CK, CK+4℃ and CK+2℃ decreased the number of central vascular bundles of third internode by 43.29% and 22.59%, respectively; CK+4℃ and CK+2℃ decreased total vascular bundle area by 40.33% and 28.68%, respectively. The effect of temperature increment on the number and area of central vascular bundle was greater than that of peripheral vascular bundle. The elevated temperature decreased the area of single peripheral and central vascular bundle, but increased that of XY335. And ZD958 had greater increment of the number of vascular bundles and area of total area of peripheral vascular bundles than XY335 under elevated temperature. Temperature increment significantly decreased the thrust resistance, puncture strength and crushing strength; Compared with CK, CK+4℃ and CK+2℃ significantly increased the thrust resistance by 50.75% and 43.75%, puncture strength by 25.41% and 29.59%, crushing strength by 22.41% and 23.58%, respectively. The thrust resistance showed significantly negative relationship with plant height, ear height and the third internode length, and positive relationship with stem diameter, moment of inertia, the number and area of peripheral vascular bundle, the number and area of central vascular bundle. XY335 and ZD958 had different responses to temperature increment in the whole season. Under elevated temperature, XY335 had higher increment of plant height, ear height, the third internode length, ear position coefficient and the stem diameter coefficient than ZD958. As the temperature rose, the area of single peripheral and central vascular bundle of ZD958 decreased, while the area of vascular bundle of XY335 increased. The decrease of the number of vascular bundle and the total area of edge vascular bundle of ZD958 was less than that of XY335. As the temperature rose, stem thrust reduction of XY335 was significantly greater than that of ZD958. XY335 showed maximum values at 25 days after silking, declined later, while ZD958 showed maximum values at the mature stage. The puncture strength and crushing strength of ZD958 were significantly negatively related to plant height, ear height and the third internode length, while positively related to stem diameter. The puncture strength of XY335 was significantly negatively related to plant height, while the crushing strength showed no significant relationship with those indexes. 【Conclusion】 Elevated temperature significantly promoted the growth and development of corn, and changed microstructure of stem, decreased the stem thrust resistance and increased lodging risk. The higher the temperature was, the greater the risk of lodging. The stem growth traits and lodging ability in different cultivars had significantly different response to elevated temperature.
【Objective】 With the continuous change of climate, the extreme weather events occurred frequently, such as high temperature, drought and their combined stress, which posed a severe challenge to maize production. This study was conducted to explore the effects of high temperature, drought and their combined stress on microstructure of stem, dry matter accumulation and distribution and grain yield of summer maize. 【Method】 Denghai 605 (DH605) was used as the experimental material. Three treatments were conducted as high temperature (T), drought (D), and the compound stress (T+D) during the flowering period for 6 days, and the natural temperature and normal moisture management as control treatment (CK). The effects of high temperature, drought and the compound stress on stem microstructure, dry matter accumulation and distribution, photosynthetic characteristics, pollen activity and yield of summer maize were investigated. 【Result】 The thickness of the cortex, the thickness of the hard skin, the total number of vascular bundles and the number of small vascular bundles in summer maize were significantly reduced after the combined stress of high temperature and drought, which decreased by 8.8%, 14.1%, 9.4%, and 13.7%, respectively, compared with CK. In addition, after high temperature and drought stress, the pollen viability, the net photosynthetic rate and total dry weight of summer maize decreased significantly, the pollen viability and net photosynthetic rate of T, D and T+D treatments decreased by 23.1%, 8.3%, 30.7% and 23.7%, 16.6%, 37.5%, respectively, compared with CK; The total dry matter accumulation of T, D and T+D at the maturity stage was decreased by 19.7%, 5.1%, and 26.6%, respectively, compared with CK, which led to a significant yield decrease of 63.2%, 13.2%, and 71.7%, respectively, compared with CK. 【Conclusion】 High temperature, drought, and the compound stress significantly caused abnormal stem development of summer maize, the decrease of dry matter accumulation, and a significant decrease of maize yield. The combined effect of high temperature and drought on the yield and resistance of summer maize was greater than the single stress of high temperature or drought.
【Objective】 As the climate change and summer maize hybrids transition, it is of great significance to study how to adjust the summer maize hybrids and sowing date to adapt the effective accumulated temperature. This study was expected to explore the influence of sowing date on the yield formation of summer maize hybrids differing in maturities, so as to provide theoretical references for the local suitable sowing date and selection of maize hybrids. 【Method】 The medium early maturing hybrids, including Denghai 518 (DH518), Jingnongke 728 (JNK728), Denghai 618 (DH618), and medium late maturing hybrids, including Zhengdan 958 (ZD958), Denghai 605 (DH605), Xianyu 335 (XY335), were selected as test materials from 2017 to 2019, and three sowing dates were set up on June 5th (E), June 15th (N) and June 25th (L). Then, the effects of sowing date on the seed setting rate and yield formation of summer maize hybrids differing in maturities were investigated. 【Result】 Compared with sowing on June 25th, the yield of the medium late maturing hybrids sowing on June 5th and the medium early maturing hybrids on June 15th was increased by 28.81% and 18.92%, respectively; the production efficiency of the effective accumulated temperature (EAT) was increased by 16.24% and 14.66%, respectively. Under the delayed the sowing date to June 25th, the 1000-kernel weights of all hybrids increased, while the kernels per ear and harvest ear number reduced, which led to the yield losses. With sowing date delayed, the EAT of all hybrids decreased by 1.21%-10.62%, and the decrease of middle late maturing hybrids was greater than that in the middle early. Besides, the total seed setting rate reduced 6.25%-19.94% in the middle early maturing hybrids, while the middle late hybrids decreased by 8.11%-27.32%, which was higher than that in the middle early hybrids. The rate of empty shot increased by 1.42%-14.72%, which was unconcerned with the maturity of hybrids. The harvest index of middle early maturing hybrids first increased and next decreased, with the range of 15.91%-20.23% when the middle late hybrids decreased by 2.36%-27.69%. The yield of different hybrids was positively correlated with EAT, while the effect of EAT from silking to maturing stage was more significant. Among the four factors of EAT, harvest index, total seed rate and the whole growth period days, the yield of middle early maturing hybrids was closely related to harvest index and total seed rate, while the yield of middle late maturing hybrids had stronger correlation with EAT and harvest index. The correlation between EAT and the whole growth period days was greater than that of total seed rate, harvest index and yield in medium early maturing hybrids, while the correlation between EAT and yield was stronger than that of harvest index, total seed rate and the whole growth period days in medium late maturing hybrids. 【Conclusion】 The yield of middle early maturing hybrids was less limited by the effective accumulated temperature. Higher harvest index and total seed setting rate could be available when the effective accumulated temperature was about 1 700℃·d in the whole growth period. The yield of middle late hybrids was limited by the effective accumulated temperature more. Above 1 800℃·d was more conductive to the increase of yield. Therefore, sowing medium late maturing hybrids around June 5th and medium early maturing hybrids around June 15th were beneficial to obtain higher yield and improve the production efficiency of effective accumulated temperature for local summer maize.
【Objective】 To provide the theoretical support on the mechanism on the sustainable production of maize under future climate change and give suggestions on associate parameter adjustment for crop models, the effects of elevated atmospheric CO2 concentrations (eCO2) and nitrogen application on the content and dynamics of different carbon and nitrogen metabolites after flowering of summer maize were studied. 【Method】 Based on the free atmospheric CO2 enrichment (FACE) platform, a field experiment was carried out with Nongda 108, a summer maize variety, as the experimental material. Two nitrogen levels (ZN-zero nitrogen and CN-180 kg N·hm-2) were set under the ambient atmospheric CO2 concentration (aCO2) of about (400±15) μmol·mol-1 and high CO2 concentration of (550±20) μmol·mol-1, respectively. The following measurements were monitored in the experiment: the maize yield and its components, accumulation of dry matter, content and dynamics of carbon metabolites, including non-structural carbohydrates (ie. soluble sugar and starch), total carbon and nitrogen metabolites including soluble nitrogen (ie. nitrate nitrogen, free amino acids, and soluble protein), and insoluble nitrogen compounds (ie. cell walls-N, thylakoid-N, and total-N), and the carbon to nitrogen ratio. 【Result】 (1) eCO2 and nitrogen application could promote the accumulation of biomass of summer maize, however the effects on maize yield and yield components were not significant. (2) Under eCO2, the concentration of soluble sugar, one of the components of carbon metabolites, showed significant increase in the functional leaves after the flowering stage, as well as the C/N ration at the late seed-filling stage. (3) Under eCO2, the concentration of essential functional N components did not show obvious variation in the functional leaves after the flowering stage, but the content of some structural nitrogen components were decreased: The content of soluble protein, the functional N component, was not affected by eCO2 in the functional leaves. The concentration of free amino acid, one of the simple N components, only showed increase at the flowering stage and then showed less change at the later growth period compared with that under aCO2. However, the content of cell wall-N and thylakoid-N, the non-soluble N components, were significantly decreased at the late period after flowering stage. (4) Nitrogen fertilizer application could increase the concentration of non-structural carbohydrates (soluble sugars) and nitrate-N significantly in functional leaves from tasseling to the later stage of filling, as well as the content of cell wall-N and thylacoid-N. However, the content of soluble protein was not affected in functional leaves without nitrogen application under the medium soil fertility. In comparison, the content of thylakoid-N and cell wall-N showed decrease in the functional leaves in the treatment without nitrogen fertilizer application, implying that nitrogen was usually preferentially supplied for the soluble protein to meet the necessary requirement of crop growth. (5) The interaction function of eCO2 and nitrogen fertilizer showed difference for varied components of the carbon and nitrogen metabolites, usually exhibited at different stages: combination of N application and eCO2 improved the concentration of simple carbon and nitrogen components, such as soluble sugars and nitrate nitrogen in the later stage of maize functional leaves, and increased the C/N ration. The content of cell wall nitrogen could be increased at the early stage of grouting for summer maize. For total nitrogen content in functional leaves, it showed decreased only at the later stage of seed filling grouting, and there was no other impact on the total nitrogen at other stages in summer maize growth period. 【Conclusion】 eCO2 had a certain effect on the biomass increase of summer maize, and the carbon nitrogen ratio of ear to leaf increase significantly in some stages, but had no significant effect on the yield. Under eCO2, the content of unstructured carbohydrates in ear leaves increased, but the total nitrogen and insoluble nitrogen compounds decreased to different degrees after flowering. Therefore, it was important to increase nitrogen application level rationally under the future climate change scenarios in which eCO2 would be one of the characteristics.
Elevated atmospheric CO2 concentration (eCO2) and warming may affect the crop photosynthesis, and consequently alter the translocation of photosynthetic carbon to soil. Under climate change, the change of photosynthetic carbon retained in soil may shape the structure of microbial community involved in photosynthetic carbon transformation. As a major driver of soil carbon cycle, soil microorganism plays an important role in the transformation of soil organic matter. The changes of microbial community structure and function under climate change are likely to affect the turnover of soil organic matter, resulting in an increase or decrease in the concentration of atmosphere CO2 as a feedback to climate change. Soil carbon balance depends on the input and output of carbon in the soil and its retention in the soil. However, it is unclear that how climate change may affect the stability of the soil carbon pool. Therefore, the change of the soil carbon pool corresponding with soil microbial community structure is the core mechanism of terrestrial ecosystem in response to climate change, which is important to the management of soil organic carbon and the maintenance of soil productivity on farmland in the future. This paper reviewed the responses of soil carbon pool and soil microbial community structure to global climate change (eCO2 and warming). The main conclusions were as follows: (1) Elevated CO2 and warming exhibited the tradeoff effect on soil carbon pools, but whether soil carbon pool became carbon source depended on the extent of warming; (2) Elevated CO2 increased the accumulation of photosynthetic carbon in plant parts of corn and wheat. Warming also posed an impact on the accumulation of photosynthetic carbon, but the impact varied among different parts with negative or no effect; (3) Warming and eCO2 showed a cumulative effect on soil microbial activity and community diversity, but different microbial kingdoms (bacteria, fungi and archaea) had different roles to affect carbon turnover. Finally, it was proposed that the future research directions included: (1) in-depth study on the impact of climate change on the turnover of root exudates considering the plant-soil interaction and its influence on microbial properties; (2) DNA-SIP being applied to explore the relationship between different plant-carbon sources utilized by soil microorganisms and carbon cycling under eCO2 and warming. Thus, these proposed studies might clarify substrate-utilizing strategies by microbes and the response of microbial community to climate change.
【Objective】 The effects of different types of nitrogen fertilizers on the diurnal variation of N2O and CO2 fluxes from spring maize soil at high latitude were explored, in order to provide a reference for nitrogen fertilizer efficient utilization management and greenhouse gas emission reduction in farmland at high latitude. 【Method】 Field micro-plot trials and the static chamber-gas chromatography method were used to investigate the effects of slow release fertilizer (SLN), urea plus nitrification inhibitor and urease inhibitor (NIUI) and ordinary urea application (OU) on the diurnal variation of N2O and CO2 emissions from spring maize fields at high latitudes. The day-night emission characteristics of soil N2O and CO2 were compared and analyzed in 6 periods, including pre-emergence stage (S1), seedling stage (S2), jointing stage (S3), filling stage (S4), dough stage (S5), and fallow period (S6). 【Result】 The diurnal variation of N2O and CO2 emissions under different nitrogen fertilizers showed a single peak trend. From stage S1 to S6, the peak of N2O emissions appeared in 13:00-19:00, and the peak valley occurred after midnight (0:00-6:00). However, there was no significant difference in CO2 fluxes between observation periods during day or night at the same stage from S2 to S5. In stage S1 and S2, the daytime emissions of N2O and CO2 accounted for 56.2%-82.3% and 53.6%-66.5% of the total emissions of the whole day, respectively. From stage S3 to S5, the ratio of N2O and CO2 emission in the daytime was 40.6%-59.6% and 43.7%-55.4%, respectively. SLN treatment reduced the soil N2O cumulative emission in stage S1, while NIUI treatment reduced the soil N2O cumulative emission at stages S1, S2 and S5, and the emission reduction period was mainly from 4:00-16:00 in the daytime of stage S1 and 12:00 to 22:00 of stage S2, among which the emission reduction from 18:00-19:00 during stage S2 accounts for 57.3% of the total emission reduction period. All time periods of day and night showed the effect of emission reduction in stage S5, and the ratio of emission reduction during day and night was almost the same. The main emission reduction periods of SLN for soil CO2 were the whole day in S1 stage and 15:00-4:00 in S3 stage, among which the emission reduction ratio of 12:00-23:00 during the S1 stage was as high as 76.8%, and the reduction ratio at night during S3 accounted for 68.1% of all emission reduction periods. NIUI treatment showed a reduction effect on CO2 emission in five monitoring days of growing season of maize, but the ratio of day-night emission reduction was different, with an average reduction of 46.9% during the day and a maximum reduction of 73.2%. It was also found that there was an extremely significant positive correlation between the daily mean of N2O and CO2 fluxes, and the observed values of 9:00-10:00 (rN2O=0.938**, rCO2=0.977**). Therefore, 9:00-10:00 could be used as the representative sampling period when conducting long-term greenhouse gas emission research in spring maize fields in Northeast China. 【Conclusion】 The diurnal emission fluxes of soil N2O and CO2 responded differently to various nitrogen fertilizations at different maize growing stages. Compared with conventional nitrogen application, SLN inhibited the soil N2O emission before maize seedling in day and night, and the emission reduction period was mainly between 9:00-22:00. SLN promoted the emission of N2O in day and night in other monitoring days. NIUI inhibited the soil N2O emission during the daytime before maize seedling, the night at the seedling stage, and the harvest stage day and night, while NIUI promoted the soil N2O emission from jointing stage to filling stage. In the whole monitoring day before seedling and the night of the monitoring day at jointing stage, SLN had a reduction effect on soil CO2. NIUI reduced soil CO2 emissions in six monitoring days.
