The Effect Of Irrigation Control Lower Limits On Soil N₂O Emissions And Microbial Functional Diversity In Greenhouse Soil

Our study investigated the effect of different irrigation control lower limits on soil nitrous oxide emissions and influence factors and examined soil microbial activity and functional diversity in a greenhouse vegetable irrigation filed in Shen yang agricultural university.The main conclusions from our study were as followed:（1）Soil nitrous oxide emissions from all treatments had no common trend during the tomato growth season.The peak of soil nitrous oxide flux would apparently occur within 1～5 days after each irrigation event;The mean and cumulative flux of nitrous oxide were significantly lower under D₃₀ treatment than those under D₂₀ and D₄₀ treatments（P<0.05）,whereas no significant difference betweem D₂₀ and D₄₀ treatments.The tomato yields under D₃₀ treatment were significantly higher than those under D₂₀ and D₄₀ treatments（P<0.05）;the cumulative irrigation amount under different irrigation control lower limits followed by 20 kpa treating>30 kPa treating>40 kPa treating.（2）Soil nitrous oxide flux was significantly related to soil moisture,NH₄^-N concentrations（P<0.01）and soil pH（P<0.05）.Soil nitrous oxide was not correlated with soil temperature and soil NO₃^--N concentrations.The AOA gene copy numbers were significantly lower under D₃₀ treatment than those under D₂₀ and D₄₀ treatments（P<0.05）;Soil nitrous oxide flux significantly related to AOA gene copy numbers（P<0.05）.There was no consistent correlation between soil nitrous oxide flux and AOB gene,denitrifier genes（nosZ,nirK,cnorB）copy numbers.（3）The microbial activity presented by microcalorimetric technique indicated that microorganisms under D₂₀ and D₃₀ treatments had more efficient metabolism,while decreased microbial activity under D₄₀ treatment was firstly due to soil pH,followed by organic matter and total N.The copy numbers of bacteria under D₂₀ and D₃₀ treatments were significantly higher（P<0.05）than those under D₄₀ treatment;the copy numbers of fungi among three treatments had no significant difference.（4）The Biolog analyses indicated that AWCD（Average Well Color Development）under D₃₀ treatment were significantly（P<0.05）higher than those under D₂₀ and D₄₀ treatments.The Shannon（H）and Simpson（D）indices among three treatments had no significant difference.The McIntosh（U）index under D₃₀ treatment was significantly higher than those under D₂₀ and D₄₀ treatments（P<0.05）.PCA analyses suggested that carbon utilization of the soil microbial communities under D₃₀ treatment in tomato soils differed markedly from D₂₀ and D₄₀ treatments.Therefore,we suggest that a lower control limits of soil suction of about 30 kPa is the optimal irrigation amount for use in vegetable production,given that lower soil nitrous oxide fluxes,higher microbial activity and functional diversity were performed while high tomato yields were maintained.