Effects Of Elevated CO₂ On Plastic Film Mulched Maize Carbon And Nitrogen Transfer And Nitrogen Regulation Mechanism In A Semiarid Region

Atmospheric CO₂ was the main component of greenhouse gases.Elevated atmospheric CO₂ concentration can stimulate plant photosynthesis and enhance plant carbon metabolism.Nitrogen is the main component of protein,which plays an important role in stem and leaf development and fruit formation.Carbon and nitrogen coordinate promote plant nutrient transformation and morphological structure building.The increase of atmospheric CO₂concentration will affect the carbon and nitrogen metabolism of plants,breaking the original carbon and nitrogen balance and affecting the growth of crops.In order to explore the effect of elevated atmospheric CO₂ concentration on carbon and nitrogen transport in maize,we initiated a field experiment in 2017,the open-top chamber?OTC?system was used to simulate the elevated CO₂ concentrations during the growing period of maize.Three atmospheric conditions were set:elevated CO₂ concentration(700?mol·mol^-1,marked as OTC+CO₂),OTC systems with the current atmospheric CO₂ concentration?marked as OTC?,and natural atmospheric CO₂ concentration?as control,marked as CK?.At the same time,four kinds of water and nitrogren treatments were included under each atmospheric conditions in the current experiment,i.e,plastic film mulching with N rate of 290kg N·hm^-2?marked as MN290?,plastic film mulching with N rate of 225kg N·hm^-2?marked as MN225?,rainfed with N rate of 225kg N·hm^-2?marked as RN225?,and rainfed without N application?marked as RN0?.Our aim was to study the response of carbon and nitrogen transport in the aboveground part of spring maize?Zea mays L.?under different water and N fertilizer conditions to the elevated CO₂.The results of this experiment are as follows.1.The effects of elevated atmospheric CO₂ concentration on organic carbon content of maize varied with different organs and growth stages.In 2017,elevated CO₂ significantly reduced the content of organic carbon in leaves for the two mulched treatments of MN290and MN225 at V9 stage,and also reduced the organic carbon content in stem for the treatment of RN0 at V6 stage,while significantly increased the organic carbon content in leaves for the treatment of MN290 at R5 stage and the treatment of RN0 at R6 stage,as well as significantly increased organic carbon content in grain for the rainfed treatments of RN225 and RN0 at R6 stage.In 2018,elevated CO₂ significantly reduced leaf organic carbon content in the two film mulched treatments of MN290 and MN225 at V9 stage.The combined effects of elevated CO₂ and OTC on organic carbon content varied with growth period and nitrogen application rate.OTC+CO₂ significantly increased the content of organic carbon in leaves of high nitrogen treatment?MN290?at R1 and R5 stages in 2017,but decreased the content of organic carbon at V9 and R6 stages;in 2018,OTC+CO₂significantly increased the content of organic carbon in grain at the R3 stage of high nitrogen treatment?MN290?,but significantly reduced the content of organic carbon for the treatments of MN225 and RN0 at R3 stage.2.The total nitrogen content in leaves and stems of maize decreased with the growth period.Under the elevated CO₂ conditions,high nitrogen can promote nitrogen accumulation in maize leaves at V6 stage.In 2018,elevated CO₂ significantly increased the total nitrogen content at V6 stage for the treatment of MN290,while significantly reduced the total nitrogen content at V6 and R3 stages of the treatment of RN0.The combined effects of elevated CO₂ and OTC on total nitrogen content varied with corn organs and growth stages and nitrogen application rates.OTC+CO₂ significantly increased the total nitrogen content in the two film mulched treatments of MN290 and MN225 at V12 stage in 2018.OTC+CO₂significantly increased the content of total nitrogen at V12 and R1 stages in the two film mulched treatments of MN290 and MN225 in 2017 and 2018,however,it significantly reduced the total nitrogen content at R3 stage of the treatment of RN0 in the two years.3.Under the elevated CO₂ conditions the change of C/N ratio at V6 stage of maize leaves was related to the amount of nitrogen applied..In 2018,elevated CO₂ significantly reduced the C/N ratio at V6 stage of the treatment of MN290,but significantly increased the C/N ratio at V6 stage of the treatment of RN0.OTC+CO₂ significantly reduced the C/N ratio at R6 stage in the two film mulched treatments of MN290 and MN225 in 2017,and significantly reduced the C/N ratio at V12 stage of the two treatment MN290 and MN225 in2017 and 2018.Meanwhile,OTC+CO₂ significantly reduced the ratio of C/N at R5 stage for the treatment of MN225 and at R6 stage for the treatment of RN0 in 2017.In conclusion,under the condition of elevated CO₂ concentration,the effects of MN290treatment,MN225 treatment and RN0 treatment on carbon and nitrogen transport in maize were significantly higher than those treated by RN225.Elevated CO₂ caused the decrease of organic carbon content at V9 stage of maize leaf in the two film mulched treatments of MN290 and MN225.Elevated CO₂ increased the total nitrogen content at V6 stage of the treatment of MN290 in maize leaves,and the C/N ratio decreased.under the condition of elevated CO₂ concentration,the effects of the treatment of RN0 and the treatment of MN290on the total nitrogen content of maize leaves at V6 stage were opposite.OTC+CO₂ increased the content of organic carbon at R3 stage of the treatment of MN290,and increased the total nitrogen content at V12 stage of the leaves and stems in the two film mulched treatments of MN290 and MN225,and the C/N ratio decreased.OTC+CO₂ reduced the content of organic carbon and total nitrogen at R3 stage of grain of the treatment of RNO.