Effects Of Elevated CO₂ On The Growth And Yield Of Rice And Wheat

With the rapid development of industry and economy in the world,CO2 concentration gradually increased due to the burning of fossil fuels.CO2 concentration has risen from 280 pmol mol'1 before the industrial revolution to 409 ?mol·mol-1 now.It is predicted that the CO2 concentration in the atmosphere will reach to 538?670 ?mol·mol-1 under the greenhouse gas emission stabilization scenario in 2100.Agriculture is one of the most sensiti-ve and vulnerable areas in response to climate change,and food production is related to national security and stability.To investigate the effects of elevated CO2 concentration levels on the rice and wheat,field experiments with simulating elevated CO2 concentration were conducted by open-top chambers(OTCs)which using a CO2 concentration automatic control system to achieve different levels of elevated CO2 concentration.CO2 concentration automatic control system consists of 12 OTCs.The experimental treatments included the ambient CO2 concentration(CK),40 ?mol·mol-1 above ambient CO2(CK+40),200 ?mol·mol-1 above ambient CO2(CK+200)during the rice growing season in 2016 and the wheat growing season in 2017.During the rice growth season in 2017,the concentration of CO2 was set as:ambient CO2 concentration(CK),80 ?mol·mol-1 above ambient CO2(CK+80),200 ?mol·mol-1 above ambient CO2(CK+200).Each treatment had four replicate plots.To study the photosynthetic characteristics of rice and wheat,growth and yield response to different levels of elevated CO2 concentration is of great significance for guiding agricultural production and ensuring food security.The results showed that Pn increased rapidly under the relatively lower PAR(lower CO2)concentration ranges and then increased slowly to the maximum value.When PAR(CO2 concentration)arrived at the saturation point,Pn tended to be stable during the rice growing season in 2016 and the wheat growing season in 2017.Compared to CK,CK+200 reduced Pn in different degrees.The photosynthetic acclimation appeared in rice leaves under CK+200 during the rice growing season in 2016 and 2017.For the wheat growing season in 2017,compared with CK,there was no photosynthetic acclimation in CK+200.The light response parameters of the rice growing season in 2016,compared to CK,CK+200 increased Pn-max.For CO2 response curve,CK+200 reduced Psat and CE.During the wheat growing season in 2017,CK+200 increased Q,Pn-max,Ic and Rd.For CO2 response curve,CK+200 increased the Psat,CE,CCP and Rp in different degrees.Compared to CK,CK+40 and CK+200 increased plant height and tiller number during the rice growing season in 2016 and the wheat growing season in 2017.During the rice growing season in 2017,the growth trend of rice was changed,the tiller number was CK+80>CK+200>CK.The increase of different CO2 levels reduced the nitrogen content of the leaves in different stages of rice and wheat,and the higher the concentration of CO2,the more the decrease of nitrogen content in leaves.The photosynthetic rate was significantly and positively correlated with the leaf nitrogen content(P<0.01),and increased with the increase of the leaf nitrogen content during the rice growing season in 2016.High concentration CO2 concentration increased the utilization efficiency of photosynthetic nitrogen in rice leaves.During the wheat growing season in 2017,the net photosynthetic rate of wheat,CK,CK+40 and CK+200 showed no correlation with nitrogen content.The increase of different CO2 levels increased the biomass of rice and wheat at different growth stages.The higher the concentration of CO2,the greater the biomass of each organ during the 2016 rice and the 2017 wheat growing season.During the rice growing season in 2017,the biomass of rice showed CK+80 were higher than CK+200.Compared to CK,CK+40 and CK+200 treatments increased the rice grain weight and grain number,and increasing the yield of rice and wheat at last during the rice growing season in 2016 and the wheat growing season in 2017.In addition,the increase of CO2 concentration leads to the increase of the empty grain size of rice,and the higher the concentration of CO2,the more empty grain.CK+200 were lower than CK during the rice growing season in 2017.In the rice growing season of 2016 and 2017,the increase of different CO2 levels reduced the rice harvest index.In the wheat growing season of 2017,CK+40 and CK+200 treatments increased wheat harvest index.