Effects Of Nitrogen Fertilization,film Mulching And Elevated CO₂ On Soil Enzyme Activities And Microbial Biomass Carbon And Nitrogen In A Spring Maize Field,Loess Plateau

The increase of atmospheric CO₂ concentration will inevitably affect the growth and development of crops and their absorption of nutrie nts,which will change the soil environment of crops.Maize was one of the main gra in crops in China,and nitrogen fertilizer plays an important role in the yie lds of food crops.Plastic film mulching cultivation techno logy is widely used to increase yield in arid areas of northern China.Therefore,it was necessary to study the effects of nitrogen fertilization,film mulching and elevated CO₂ on soil enzyme activities and microbial biomass of maize in semiarid cropland,which was of great significance for understanding soil nutrient transformation and energy metabolism.A field experiment was conducted in a semiarid area to investigate the response of soil enzyme activities and microbial biomass to climate change in a farmland of spring maize.Open-top chamber?OTC?system was used to control elevated CO₂ concentrations(700?mol·mol^-1,marked as OTC+CO₂)during the growing period of maize.At the same time,OTC systems with the current atmospheric CO₂ concentration?marked as OTC?and natural atmospheric CO₂ concentration?control,marked as CK?were also set up.The soil enzyme activities,microbial biomass carbon and nitrogen in treatment of RN0?rainfed,no N?,RN225(rainfed,225kg N·hm^-2),MN225(mulc hed with plastic film,225kg N·hm^-2)and MN290(mulc hed with plastic film,290kg N·hm^-2)at the different growth stages of spring maize were measured.The purpose of this experiment was to provide scientific basis for further revealing the ecological process of farmland soil under future climatic conditions,seeking a soil biochemical environment that ensures high and stable yield of crops,and improving soil biological fertility.The main conclusions are as follows:?1?The effect of elevated CO₂ on soil enzyme activities in spring maize farmland varied with the growth period and the enzyme.Further,under the current experimental conditions?MN225?,the effect of OTC on soil enzyme activities was more significant than that of elevated CO₂.?2?Compared with RN0,RN225 treatment increased the activity of soil urease,alkaline phosphatase and sucrase by 14.25%¹7.29%,6.13%⁷.49%and 49.51%⁵1.47%,respectively,while under the condition of film mulching,excessive nitrogen application had no effect on soil enzyme activity.The film mulching treatment reduced the soil urease,alkaline phosphatase and sucrase activities at multiple growth stages.?3?The content of soil microbial biomass carbon and nitrogen in rhizosphere was higher than that in bulk,and the increase range was 13.15%²40.83%and 11.95%¹18.65%,respectively.?4?The effect of OTC and elevated CO₂ on soil microbial biomass carbon and nitrogen in spring maize cropland varied with the rhizosphere environment,the growth stage and the management patterns of water and fertilizer.The response of soil microbial biomass carbon and nitrogen in rhizosphere and bulk to OTC and e levated CO₂ was not completely consistent.Under different water and fertilizer management patterns,the effect of OTC on rhizosphere and non-rhizosphere soil microbial biomass carbon and non-rhizosphere soil microbial biomass nitrogen was more significant than that of elevated CO₂,and growth stage was an important factor that affected soil microbial biomass carbon and nitrogen in maize cropland.?5?Compared with RN0,proper nitrogen fertilization?RN225 treatment?increased the content of soil microbial biomass carbon and nitrogen,while under the condition of film mulching,excessive nitrogen application decreased the content of soil microbial biomass nitrogen.The film mulching treatment reduced the content of soil microbial biomass carbon and nitrogen at several growth stages.In addition,the soil microbial biomass carbon and nitrogen in rhizosphere was more sensitive to nitrogen application and plastic film mulching than non-rhizosphere.In summary,the effects of nitrogen application,film mulching and elevated CO₂concentration on soil enzyme activites and microbial biomass carbon and nitrogen was related to crop growth stage,the enzyme and rhizosphere environment etc.The results provided data support for improving soil quality of spring maize field in arid and semi-arid areas of Loess Plateau under the condition of climate change.