Response Of Maize/Soybean Intercropping System To CO₂Concentration Enrichment And Phosphorus Nutrient Regulation

Atmospheric CO₂concentration is rising, predicted to cause global warming, and alterprecipitation patterns. The change will inevitably have direct or indirect effects on the processof physiology, growth and development of related crops, and, accordingly, have effect on theyield and quality of crops. As a result, the whole agricultural production systems will need tobe adapted. Characterized by taking full advantage of resources and largely increasing yield,the intercropping pattern, as an important part of our traditional intensive and meticulousfarming, is a practical way to resolve the contradiction between continued population growthand constantly farmland decrease. Previously, numerous studies have been done on growthand development of crops in maize/soybean intercropping system, but there are relatively lessresearches involving effects of CO₂concentration enrichment, planting patterns and P supplyon them. Therefore, the controlled hydroponics and pot simulation experiments wereconducted in the tall plant growth room with microclimate controlling （AGC-DOO3N）. Thecrops were grown at two levels of CO₂（380μmol.mol-1and760μmol.mol-1）, three plantingpatterns （maize monoculture, soybean monoculture and maize/soybean intercrop） and twophosphorus application （phosphorus deficiency and phosphorus supply）. Treatment effectswere measured on the growth, photosynthetic fluorescence characteristic, root parameters,nutrient absorption and interspecies competition. Further analysis was made to investigate theregulatory effects of phosphorus application on them. The main results are as follows:1. CO₂concentration enrichment overall stimulated plant height, stem diameter, leaf area,root system characteristics and photosynthetic fluorescence parameters of maize and soybeanunder different cropping patterns. This kind of positive effect could be enhanced by P supply.The impact of intercropping pattern on crop growth depended on the species of the crop itself.CO₂concentration and P supply had more significant effect on intercropping maize thanmonoculture group and had a bigger impact on monoculture soybean.2．Whether it was phosphorus deficiency or not, still, CO₂concentration enrichment wouldremarkably increase the organic dry matter accumulation of maize and soybean in all plantingpatterns. The promotion to the underground part was more evident than that to the aboveground. As a result, root shoot ratios of both two crops were increased. In themaize-soybean intercropping system, LER value was greater than1and Ams value wasgreater than0, which indicated that maize held the intercropping had advantage in this system.The elevated CO₂concentration and P supply significantly increased the values of LER andAms, which showed that CO₂concentration enrichment and P supply could enhance thisadvantage.3. In compared with those groups under background CO₂concentration, the N and Pcontents increased in fruits of soybean and maize from both planting patterns under doubledCO₂concentration and the difference was significant with P supply. Besides, under bothconcentrations, the N and P contents of fruits of P supply groups were remarkably higher thanthat of P deficiency groups, and under both P conditions, N and P contents in fruits ofintercrop maize were significantly higher than those of monoculture groups. But the P contentin fruits of intercrop soybean with P supply notably decreased. Whether it was P supply or Pdeficiency, under both CO₂concentrations, In maize/soybean intercropping system, therelative N and P nutrient uptake competitiveness of maize was greater than soybean and thecompetitiveness of maize of P supply group was notably higher than that of P deficiencygroup. Elevated CO₂concentration significantly increased P supply maize competitiveness inN uptake against soybean, which indicated that CO₂concentration enrichment and P supplyhad positive reciprocal effects on N uptake competitiveness of maize against soybean in theintercropping system.Results above showed that the impact of CO₂concentration and P supply on canopy trait,photosynthetic fluorescence parameters, root system characteristics and nutrient uptake ofintercropping maize was more evident than on those of monoculture group. But thedifference is not significant between two planting patterns of soybean. CO₂concentration andP supply could significantly increase values of LER and Ams. The CO₂concentrationenrichment can notably improve the maize competitiveness of N uptake against that ofsoybean, which indicated that CO₂concentration enrichment and P supply had positivereciprocal effects on N uptake competitiveness of maize against soybean in the intercroppingsystem.