Photosynthetic Physio-ecological Mechanism Of Intercropping Wheat And Maize Adapted To High Plant Density

Aiming at the problem of abundant light and heat resources in Hexi oasis irrigation area,but the utilization rate of traditional single cropping mode is not high,this paper integrated intercropping and dense planting,studied the key physiology(net assimilation rate,photosynthetic parameters,photodynamic parameters of chlorophyll silver,etc.),ecology(canopy transmittance,population CO2 concentration,relative humidity of atmosphere,etc.)of wheat-maize intercropping under different plant density conditions.Indicators to clarify the relationship between the indicators and crop productivity,reveal the photosynthetic physiological and ecological mechanism of wheat-maize intercropping.The main conclusions are as follows:(1)Intercropping significantly increased net assimilation rate(NAR),photosynthetic rate,intercellular CO2 concentration and decreased transpiration rate of wheat and maize,compared with monoculture.Increase of the planting density of intercropping wheat significantly reduced wheat NAR,which was not conducive to the accumulation of photosynthetic substances in crops to grain and biological yield;in wheat-maize intercrops,enhancement of the planting density of maize increased the green leaf area of maize populations and delayed the senescence process of maize in the later period of growth,however,higher planting density could easily cause reduction of crop yield.The change of intercropping wheat density had no significant effect on chlorophyll fluorescence parameters;the enhancement of intercropping maize density promoted the increase of the ratio of Fv/Fo and Fv/Fm,and when the planting density exceeded a certain threshold,their values decreased;the decrease of q P enhanced the adaptation of crops to weak light in intercropping systems.Therefore,the appropriate increase of maize density provided an excellent intracellular environment for maize growth in wheatmaize intercrops.(2)Maize planting density significantly affected canopy transmittance in the middle-lower layers of crop,in wheat-maize intercrops,maize transmittance in the high-density maize and low-density wheat pattern significantly decreased by 7.6%,compared with the high-density maize and high-density wheat pattern.Reduction of wheat density in intercropping pattern could significantly increase CO2 concentration of intercropping wheat population and CO2 concentration of maize population before wheat harvest,however,which decreased CO2 concentration of intercropping maize population after wheat harvest.In wheat-maize intercrops,maize density significantly increased the CO2 concentration of wheat population,but that had no significant influence on the CO2 concentration of maize population.The change of intercropping density significantly affected the atmospheric humidity of wheat,but had no significant influence on the atmospheric humidity of maize.The atmospheric humidity of intercropping wheat and maize which after wheat harvest was significantly affected by wheat density,however,it was not significantly influenced the atmospheric humidity of intercropping maize before wheat harvest.Appropriate increase of intercropping maize planting density could reduce the atmospheric humidity of maize.Over all,in wheat-maize intercrops,increasing of maize density and monoculture of maize with higher density optimized the growth environment of intercropping wheat and maize population.(3)The mixed grain yield of low-density wheat and medium-density maize(W1M2)pattern was significantly higher than the weighted average of grain yield under the monoculture of the same planting density,increased by 31.2%.Intercropping planting density also significantly improved the crop biomass and grain yield.The crop biomass and grain yield under W1M2 pattern significantly higher than other intercropping patterns,the highest crop biomass was 28951 kg hm-2 and the highest grain yield was 14603 kg hm-2.In summary,in intercropping pattern of low-density wheat and medium-density maize,the physiological and ecological indexes,as well as crop biomass and grain yield were the highest,appropriate increase of maize density could improve density-tolerance in wheat-maize intercrops.