Effects Of Interaction Between Elevated Atmospheric CO₂ Concentration And Nitrogen Fertilizer On The Photosynthesis And Metabolism Of Carbon And Nitrogen For Maize

Global climate change has been confirmed by the scientific community as to be mainly reflected in the elevated CO₂ concentration,temperature rise and changes in precipitation patterns.The impact of climate change on C₃ Crops,more specifically on nitrogen which is an important element needed by enzymes responsible for plant growth has been extensively researched on compared to C₄ crops like Maize.Maize being one of the most widely planted C₄ crops in the world and more specifically in China,this study aimed at analyzing the effects of elevated atmospheric CO₂ concentration?eCO₂?on maize growth under different nitrogen supply conditions.A Free Air CO₂ Enrichment?FACE?facility was used in the study to analyze the effects of elevated CO₂ concentration and nitrogen fertilizer on maize growth.The FACE facility has 6 octagon loops for eCO₂[?550±15??mol·mol-1]and another 6octagon loops for ambient CO₂ concentration[aCO₂,?400±15??mol·mol-1],of which 3 eCO₂experimental loops and 3 aCO₂ experimental loops are applied with conventional nitrogen fertilizer[180 kg?N?·hm^-2],and the rest are low nitrogen[72 kg?N?·hm^-2]application treatments.Twelve experimental loops were arranged randomly in the maize field,with the maize plant spacing of 25 cm and a row spacing of 60 cm.In the set-up treatments the following variables were recorded:plant height,leaf area,yield,photosynthesis and fluorescence parameters,carbon and nitrogen content of different forms of maize after silking.The findings indicated the following:1.Photosynthetic and fluorescence parameters:With the increase of atmospheric CO₂concentration,the total chlorophyll content of maize functional leaves increased trend in numerical value.Appropriately increasing the amount of nitrogen application increased the chlorophyll content of maize at the 12th leaf stage and 33 days after silking.Under reasonable nitrogen application conditions,increasing the amount of nitrogen application has a positive effect on the promotion of net photosynthetic rate under high concentration of CO₂.Under the condition of eCO₂,the intercellular CO₂concentration of maize leaves increased by 39.6%-57.8%.The increased atmospheric CO₂ concentration coupled with increased the intercellular CO₂ concentration due to conventional nitrogen application significantly increased the intercellular CO₂ concentration of maize leaves at the silking stage and 20days after silking.The stomatal conductance of leaves decreased and the water use efficiency of leaves increased with the eCO₂ at the silking stage and 33 days after silking.The water use efficiency of maize leaves was reduced by 10.6%and 21.0%by conventional nitrogen application at the silking stage and20 days after silking respectively.The data results show that the maize leaves had the highest water use efficiency value at LN-eCO₂ treatment,and therefore under the condition of increasing atmospheric CO₂ concentration in the future,the combination of nitrogen fertilizer and water management can achieve the goals of water saving and full utilization of atmospheric CO₂ fertilizer efficiency.eCO₂promoted the effective quantum yield of PSII in maize functional leaves.The increase of CO₂concentration caused the non-photochemical quenching?NPQ?value of maize functional leaves to decreased,hence reducing the waste of absorbed light energy in the form of heat dispersion thereby playing a certain role in improving the photosynthetic capacity of maize.2.Plant height,leaf area and yield:Elevated CO₂ concentration had no significant effect on the plant height and leaf area of maize,but the conventional nitrogen application level increased the plant height and leaf area of maize.The plant height of the maize and leaf areas have the largest values under CN-eCO₂ treatment.Elevated CO₂ did not change the components of yield nor the maize yield.Appropriate increase in nitrogen application rate can significantly increase the ear length,1000-kernel weight and thus the maize yield.3.Soluble sugar concentration of ear leaf after silking:Elevated CO₂ concentration can promote the soluble sugar concentration of maize ear leaves.Appropriately increasing the amount of nitrogen applied increased the concentration of soluble sugar in the ear leaf of maize.The CN-eCO₂ treatment significantly increased soluble sugar concentration by 32.0%to 44.0%compared with LN-aCO₂treatment,this indicated that under the condition of increasing atmospheric CO₂ concentration in the future,an appropriate amount of increased nitrogen application had a positive effect on the promotion of soluble sugar concentration in the ear leaf after the silking of maize,and thus had an effect on the growth and final yield of maize after the silking period.4.Different forms of nitrogen content in the ear leaf after silking:With the increase of atmospheric CO₂ concentration,the nitrate concentration of ear leaf had a decreasing trend.The nitrate concentration of ear leaf increased at the silking stage when the level of nitrogen application increased.Elevated atmospheric CO₂ concentration had little effect on the concentration of free amino acids in maize leaves.Compared with low nitrogen levels,the amino acid concentration of leaves at conventional nitrogen application levels increased by 14.1%-31.5%after silking.The increase of CO₂ concentration and its interaction with nitrogen fertilizer had no significant effect on the amino acid concentration of leaves.The elevation of atmospheric CO₂ concentration had a decreasing trend on the soluble protein concentration in the ear leaf of maize after silking,but the effect was not significant.5.Carbon and nitrogen content in different organs after silking:There was no significant effect of elevated CO₂ concentration on carbon content in the leaves,stems and grains of maize after silking.Appropriately increasing the amount of nitrogen applied will increase the carbon content of the maize stalk during the silking stage to maturity.After 33 days after silking in maize,eCO₂ significantly reduced the nitrogen content of leaves and stalks.Appropriately increasing the amount of nitrogen applied makes the nitrogen content of leaves and stalks after silking to reduce the carbon to nitrogen ratio of maize stalks.The interaction of elevated CO₂ concentration and nitrogen fertilizer has no significant effect on the carbon and nitrogen contents of different organs after silking.Atmospheric CO₂concentration has little effect on nitrogen use efficiency of maize.In conclusion,the increase of atmospheric CO₂ concentrations led to the increase of intercellular CO₂ concentration of maize leaves,thus reducing the stomatal conductance and improving the water use efficiency but this was not reflected in the increase of maize yield.Sufficient nitrogen application increased the concentration of soluble sugars and amino acids in maize leaves and nitrogen content in leaves and stems increased and decreased C/N ratio of stalks.Under the experimental conditions,the increase of atmospheric CO₂ concentration had no significant effect on the biomass and yield of maize,while sufficient nitrogen application had positive effects on ear length,1000-kernel weight and yield.There was no significant interaction between the measurement indexes and the increase of atmospheric CO₂ concentration and nitrogen fertilizer interaction for most of the growth stage of maize.