The Characteristics Of Soil CO₂ Emission And Its Impact Factors Of Greenhouse Soil Under Different Controlled Irrigation Low Limits

With the popularization of agricultural technology,film mulched drip irrigation have gradually become the main irrigation method in greenhouse.However,due to the lack of scientific guidance,vegetable farmers can only irrigate according to experience,resulting in a certain randomness in the amount and frequency of irrigation.Soil moisture can not only affect soil CO₂ emissions,but also affect soil physicochemical properties and soil microbial community structure.Therefore,in this study,the greenhouse soil under film mulched drip irrigation for 7 consecutive years in Shenyang Agricultural University was taken as the research object.Adopting LI-8100 A Automated Soil CO₂ Flux System and high-throughput sequencing technology,the effects of soil CO₂ emission characteristics,soil physicochemical properties,bacterial community structure and their interrelations were studied under 3 controlled irrigation low limits?20 k Pa,30 k Pa,40 k Pa?.The results of this study were expected to provide theoretical basis for scientific evaluation of greenhouse soil quality,regulation of soil carbon emissions,and promotion of soil bacterial community diversity and formulation of reasonable irrigation management measures.The main research results were as follows:?1?During the growth period of tomato,the soil CO₂ emission flux under different controlled irrigation low limits treatments reached its peak on June 24,with DI20 treatment being the highest,followed by DI30 treatment and DI40 treatment being the lowest.The cumulative emissions of soil CO₂ under DI20 treatment was significantly higher than those under DI30 and DI40 treatments?P<0.05?.However,compared with DI40 treatment,DI30 treatment had no significant increase?P>0.05?.The yield of tomato under different irrigation treatments was: DI30>DI20>DI40.The total irrigation amount and irrigation times were DI20>DI30>DI40,and the water use efficiency was DI40 > DI30 > DI20.?2?DI20 treatment significantly reduced soil organic carbon,soil p H,soil available nutrients and soil total nitrogen content compared with DI30 and DI40 treatments?P<0.05?.But soil water content in the DI20 treatment was significantly increased?P<0.05?.Soil temperature,soil bulk density and soil porosity were different among irrigation treatments,but there was no significant difference among irrigation treatments?P>0.05?.In terms of soil active organic carbon components,DI40 treatment significantly reduced soil microbial biomass carbon and readily oxidizable carbon content compared with DI20 and DI30 treatments,but also significantly increased soil particulate organic carbon and light faction organic carbon content?P<0.05?.?3?The changes of soil CO₂ emission was better explained by the two-factor model of soil temperature and soil water content?P<0.01,R2=0.685⁰.838?.This showed that the changes of soil hydrothermal environment caused by different controlled irrigation low limits would lead to changes of soil CO₂ emission flux.According to Pearson correlation analysis,Soil p H,soil total nitrogen,soil organic carbon and active components,and soil available nutrients significantly affected soil CO₂ emissions?P<0.05?.After principal component analysis of 8 indexes of soil available nutrients,organic carbon and total nitrogen,which had significant impact on soil CO₂ emissions,2 principal components were extracted.The PCA1 was composed of soil available potassium,total nitrogen,available nitrogen,water content,available phosphorus,organic carbon and p H.The PCA2 was composed of soil temperature.The cumulative contribution rate of the two principal components extracted by PCA analysis was 85.79%.?4?Through high-throughput sequencing technology,DI30 treatment significantly increased diversity index of soil bacteria Chao1 and Ace?P<0.05?compared with DI20 treatment.But there was no significant difference between DI30 and DI40 treatments?P<0.05?.Proteobacteria and Actinobacteria were the main dominant phylum under different controlled irrigation low limits.Gammaproteobacteria,unidentified_Actinobacteria,and Alphaproteobacteria were the main dominant class.?5?The Spearman correlation analysis showed that soil physicochemical properties were significantly correlated with species at the level of soil bacteria phylum and class?P<0.05?.Under this test condition,the relationship between soil CO₂ emissions under different controlled irrigation low limits and soil bacteria Chao1 index and Ace index was significantly negative?P<0.05?,while the relationship with Shannon index and Simpson index was very small?P>0.05?.Therefore,considering soil bacterial community structure,irrigation amount,soil CO₂ emissions,soil physicochemical properties and yield,under the condition of greenhouse,the lower limit of irrigation control of 30 k Pa is a better irrigation management measure.This can not only improve the soil fertility and promote soil bacterial community diversity,but also save water,increase tomato yield and effectively control soil CO₂ emissions.