Effects Of Elevated CO₂ On Soil Microbial Biomass Carbon And Nitrogen And Mineral Nitrogen Of Maize Field In A Semiarid Area

A field experiment was conducted in Changwu Agricultural and Ecological Experiment Station in northwest China from 2016 to 2017.In the current experiment,maize crop,as the subject of study,were grown in field conditions and open top chambers under the conditions of ambient and elevated CO₂ concentration of700?mol·mol^-1.Open top chambers with CO₂ concentration of 700?mol·mol^-1 were used to simulate the future atmospheric environment with elevated CO₂.The soil microbial biomass carbon,microbial biomass nitrogen and mineral nitrogen in treatment of MN₂₉₀(mulched with plastic film,290kg N·ha^-1),MN₂₂₅(mulched with plastic film,225kg N·ha^-1),RN₂₂₅(rainfed,225kg N·ha^-1)and RN₀?rainfed,no N?were analyzed through the two years.The purpose of this experiment was to provide scientific basis for deeper understanding the response of maize in arid and semiarid region to the global climate change.The main results as bellow:1.The content of soil microbial biomass carbon in 20³0cm depth was less than0¹0cm and 10²0cm for all the treatments in 2016 and 2017.Under the condition of MN₂₉₀,compared with natural atmospheric conditions with current CO₂ concentration,elevated CO₂ concentration significantly increased soil microbial biomass carbon in different soil depth in maize silking stage in 2016?P?0.05?,and the range was39.07%¹03.99%.For all the treatments including MN₂₉₀,MN₂₂₅,RN₂₂₅ and RN₀,compared with natural atmospheric conditions with current CO₂ concentration,elevated CO₂ concentration significantly increased soil microbial biomass carbon in different soil depth in maize jointing stage and physiological maturity stage in2017?P?0.05?,and the range were 60.28%²37.12%and 44.23%¹29.44%.Compared with natural atmospheric conditions with current CO₂ concentration,elevated CO₂concentration significantly decreased soil microbial biomass carbon in different soil depth for the treatments of MN₂₂₅ in big trumpet stage and RN₂₂₅ in maize silking stage in 2016,and RN₂₂₅ in maize milk-ripe stage in 2017?P?0.05?,and the range were28.63%⁴5.63%,19.57%⁴6.90%and 39.11%⁴7.29%,while elevated CO₂ no impact on the other growth stages?P?0.05?.2.The results showed that the content of soil microbial biomass nitrogen for all the treatments in 2016 and 2017 tended to decrease with the increment of the depth of soil layer.And the maximum of its content was found in maize jointing stage in 2017.Elevated CO₂ concentration significantly increased the soil microbial biomass nitrogen for all the treatments compared with natural atmospheric conditions with current CO₂concentration?P?0.05?.When mulched with plastic film,the impact of elevated CO₂concentration was more obvious,the increase rate in the treatments of MN₂₉₀ and MN₂₂₅ was larger than RN₂₂₅ in maize growth stage in 2017.3.Compared with natural atmospheric conditions with current CO₂ concentration,under the conditions of MN₂₉₀,MN₂₂₅ and RN₂₂₅,elevated CO₂ significantly increased the soil nitrate nitrogen and ammonium nitrogen?P?0.05?,eapecially under the conditions of MN_225,while elevated CO₂ no impact on the other growth stages?P?0.05?.