| Due to the precipitation is concentrated in the summer season, the precipitationduring June to September accounts for50%~80%of annual precipitation, which results infrequently flooding disaster along the Huaihe River and huge losses to local rural. The flooding disasteraffects the yield increased of wheat, rice and corn, therefore leads to food production potential to playalong Huaihe River.How to improve the production capacity along the area of huaihe River, and reducethe effect of waterlogging on wheat and corn yield are related to the development of national foodindustry. Based on the problems existing in production, the present study was conducted toinvestigate the physiological and ecological effects of different nitrogen fertilization on wheat andcorn under waterlogging environment, to find out the reasonable nitrogen fertilization alongHuaihe River. Thus to provide theoretical and practical basis for realizing mechanization ofthe compensation effect of nitrogen and high-efficiency cultivation of wheat and corn. Themain contents and results are as follows:1Effects of waterlogging stress on eco-physiological characteristics and grain yield of winterwheat and nitrogen regulationTo understand the response of number and weight of grain at different spikeletposition and grain position, chlorophyll fluorescence parameters of wheat flag leaf towaterlogging stress at booting stage and the effect of N fertilization, we carried out a fieldexperiment from autumn of2008to summer of2010using winter wheat cultivar―Wanmai54‖as material. The waterlogging stress was imposed for7d at booting stage. Fournitrogen treatments were designed for waterlogging stress and the control (normal watering)of which N application rate was240kg ha-1in all treatments but with different proportionsat land preparation, jointing, and booting stage (10:0:0for N1,7:3:0for N2,5:5:0for N3,nd3:5:2for N4) the results showed that (1) The maximum chlorophyll content of flagleaves occurred at the booting stage. Under normal watering condition, Fv/Fm, Fv/Fo, andqP showed―high-low‖variation, and the maximum values were observed between May3 and May11. However, under waterlogging stress at booting stage, Fv/Fm, Fv/Fo, and qPshowed "low-high-low" curve. Compared to control treatment, waterlogging at bootingstage significantly decreased Fv/Fm, Fv/Fo, qp, andPSII(P<0.05), and NPQ significantlyincreased (P<0.05). With the delay of nitrogen fertilization, Fv/Fm, Fv/Fo, qP, andPSIIincreased significantly compared to the forward nitrogen fertilization treatments. Postponeof nitrogen supply improved photosynthetic capacity by increasing photosynthetic pigmentcontents, and enhancing photosynthetic efficiency under water deficit. The chlorophyllcontent was positively correlated with Fv/Fm, qP, andPSII(P<0.05), but negativelycorrelated relationship with NPQ (P<0.01). From the chlorophyll fluorescence rapid lightcurves, we found that, compared to normal watering, waterlogging stress at booting stagesignificantly decreased the maximal relative electron transport rate (ETRmax), initial slope(), and half saturation point of light intensity (Ek). Postpone of nitrogen fertilizerapplication alleviated the photodamage to PSΙΙ caused by water stress, and thecompensation effect of late nitrogen fertilization occurred earlier than that of early nitrogenfertilization.(2) Waterlogging stress in the booting stage significantly decreased thenitrogen content of different organs, and decreased translocation of nitrogen stored invegetative organs before anthesis. Postpone of nitrogen application can increase thenitrogen content and translocation rate before anthesis, which resulted in adequate nitrogensupplied in the later stage of wheat.(3) Waterlogging stress decreased filling period, andfilling rate. Postpone of nitrogen application can resulte in longer filling period, highermean filling rate, and ultimately increased1000-grain weight. The research of fillingcharacterics of different grain and spike positon indicated that potential grain weight (K)of1stwas higher than that of2nd, potential grain weight (K)of main stem was higher than1sttiller and2ndtiller.(4) Seed-setting characteristics of main stem were superior to tillerspike. In the N1treatment the sterile spikelet per spike was significantly increased, and thegrain number per spike was significantly decreased. Compared with N4treatment, sterilespikelet per spike of N1treatment increased by25.5%and29.8%in2008-2009and2009-2010growing seasons, respectively. The grain number per spike of N1treatmentdecreased by5.7%. Waterlogging had greater effect on the tiller spike than the main stemspike. Waterlogging at booting stage significantly increased sterile spikelet per spike by10.6%and4.5%, and the grain number per spike decreased by2.8%and1.4%in the twogrowing seasons, especially for spike with four grains on main stem and three grains perspike of tiller spike, the grain weight in the third and the fourth grain positions. With thedelay of nitrogen fertilization, spikelet per spike, single weight per spike increased significantly, the sterile spikelet per spike decreased compared to the prior N fertilizationtreatments. Postponed nitrogen fertilization could compensate the decrease of spike withthree and four grains and increase the grain weight in third and the fourth grain positionsunder waterlogged environment at booting stage, increase the contribution rate of the thirdand the fourth grains weight to the grain weight per spike. Therefore, with the postponednitrogen fertilization, grain yield and spikelet grain number and grain weight at differentspikelet of wheat were enhanced. Results indicate that postponed N fertilization alleviatesthe effect of waterlogging at booting stage on the seed-setting characterisitics of spike andsingle grain weight.2Effects of waterlogging stress on eco-physiological characteristics and grain yield of summermaize and nitrogen regulationTo understand the response of chlorophyll (Chl) fluorescence parameters,photosynthetic pigment contents, leaf area index (LAI), rapid light curve (RLC) and grainyield of maize to waterlogging stress at seedling stage and the effect of N fertilizationregulation, we carried out a field experiment from2009to2011using summer maizecultivar "Zhengdan958" as material. The waterlogging stress was imposed for7d atseedling stage. Four N treatments were designed for waterlogging stress and the control(normal watering) of which N application rate was240kg ha-1in all treatments but withdifferent proportions at land preparation, jointing, and big trumpet stage (10:0:0for N1,7:3:0for N2,5:5:0for N3, nd3:5:2for N4) the results showed that (1) Waterlogging stressin the seedling stage significantly decreased leaf area index (LAI), especially LAI ofunder-ear layer, which resuted in earlier death of leaf. The nutrient element prior to the earlayer leaf under waterlogging stress in order to ensure the photosynthetic product suppliedand translocated to grain. Postpone of nitrogen application can increased the LAI of earlayer and above-ear layer to compensate the decrease of under-ear layer, and thecompensation effect was higher than the decrease effect of waterlogging stress, whichresulted in higher LAI compared to the earlier nitrogen application.(2) Waterlogging stressdecrease the maximal efficiency of PSII photochemistry (Fv/Fm) in dark-adapted leaves.Moreover, the contents of Chl and Chla/b, the actual PSII efficiency (PSII), photochemicalquenching coefficient (qP), and the fraction of light used in PSII photochemistry (P%) alsodropped under waterlogging stress. But non-photochemical quenching (NPQ), thermalenergy dissipation (D%), and excess of energy excitation (X%) showed different responsewhich increased under waterlogging stress. As to different N fertilization, postpone of Nsupply could improve photosynthetic capacity by increasing LAI, Chl contents, and alleviating the photosynthetic efficiency decrease under waterlogging stress. From thechlorophyll fluorescence rapid light curves, The results showed that compared with control,waterlogging stress at seedling stage significantly decreased the maximal relative electrontransport rate (ETRmax), initial slope (), and half saturation point of light intensity (Ek).Postpone of N fertilizer application alleviated the photodamage to PSΙΙ caused bywaterlogging stress, and the compensation effect of late N fertilization occurred earlierthan that of early N fertilization. Photosynthetic characters of maize under waterloggingstress at seedling stage exhibited positive responses to N supply which indicates thatpostpone of N fertilizer supply is recommended to improve photosynthetic efficiency andalleviate photodamage under waterlogging stress at seedling stage.(3) Waterlogging stressin the seedling stage can significantly decreased nitrogen accumulation of different organsand can increase the nitrogen translocation of stem, which also can increase the nitrogentranslocation of ear layer leaf and resulted in earlier death of ear layer leaf. Postpone ofnitrogen application can increase the nitrogen content of different organs, nitrogentranslocation of under-ear layer and above-ear layer leaf and decrease the translocation ofear layer leaf, which resulted in adequate nitrogen in the later stage of maize and increasedthe nitrogen uptake efficiency and partial factor productivity from applied nitrogen.(4)The dry matter accumulation after flowering stage is close to the grain yield. Waterloggingstress in the seedling stage can significantly decreased the dry matter accumulation afterflowering stage. Postpone of nitrogen application can enhance the accumulation of drymatter and lay the foundation for increased grain yield.(5) Waterlogging stress in theseedling stage decreased filling rate. With the postpone of planting data, the potential grainweight (K) decreased, the filling period decreased. Waterlogging stress decreased K andaverage filling rate (Va), and earlier reached the maximum filling rate (Vm), which maininfluence the Vaof fast filling stage and slow filling stage. Postpone of nitrogen applicationcan compensate the decrease of Vaand filling period (T).(6) Waterlogging stress in theseedling stage significantly decreased grain yield of about24.2%~28.8%, grain/leaves andharvest index decreased. The influence of waterlogging stress enhanced with postpone ofplating date. Postpone of nitrogen application can compensate the decrease trendecny ofgrain yield, but the compensate effect weakened with postpone of plating dateAll the resultes indicated that proper postpone of nitrogen application underwaterlogging stress or supply nitrogen timely after waterlogging stress can alleviate theeffect of waterlogging stress on wheat and maize. |
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