Effects Of Drip Irrigation Under Plastic Film On Soil Aggregate Stability And Arbuscular Mycorrhizal Fungi Communities In Soil Aggregate

Irrigation is the main source of soil moisture and affects the soil structure stability under greenhouse condition.The irrigation experiments were conducted in a greenhouse at the scientific research base of Shenyang Agricultural University,China during the period from 2011to 2016.The test crop was tomato,and the planting mode was ridge and furrow covering.Different controlled irrigation low limits were set to:20 kPa?D20?,30 kPa?D30?,40 kPa?D40?,respectively,and the irrigation allowable upper limit of them was set to 6 kPa.Soil water suctions detected by tensiometers were placed in 30 cm soil layer.Our study investigated the effect of different irrigation regimes on stability characteristics of soil aggregate,contents of nutrients and glomalin-related soil protein?GRSP?and communities of arbuscular mycorrhizal fungi?AMF?.The main conclusions from our study were as followed:?1?In the 0³0 cm soil layer,the size class of dry-stable aggregate was mainly composed of>2 mm and 1⁰.25 mm?23.01%³9.98%?;the size class of water-stable aggregate was mainly composed of 1⁰.25 and 0.25⁰.053 mm?31.08%⁴7.27%?.In the 0²0 cm soil layer,R_0.25,GMD and MWD in D30 treatment were significantly higher than those of D20 and D30 treatments.Overall,compared with D20 and D40,D30 treatment significantly reduced the fractal dimension?D?in the aggregates.?2?Compared to D20 and D40 treatments,the concentrations of soil organic carbon?SOC?,total nitrogen?TN?,T-GRSP and EE-GRSP in the D30 treatment were significantly increased in the macro aggregates?>0.25 mm??P<0.05?.Meanwhile,the soil enzyme activities differed with aggregates particle size.The urease and invertase activities were enhanced with the size of aggregates decreasing and the highest in<0.053 mm aggregates.In addition,the 1⁰.25mm aggregates contributed the highest nutrient contents and enzyme activities to the bulk soil.Correlation analysis showed that MWD was highly positively correlated with T-GRSP,EE-GRSP,SOC and the urease activity?P<0.01?,and the contents of T-GRSP and EE-GRSP was highly positively correlated with SOC and the urease activity?P<0.01?.?3?The chao1 and ACE indices of aggregates for D20 and D40 treatments were lower than those of the D30 treatment,indicating that the dominant AM fungal populations were affected by irrigation regimes.Three of the dominant genera Ambispora and Glomus were found in all aggregates,but another dominant genus Archaeospora was found only in the 1-0.25 mm aggregate.GRSP concentrations are key factors in determining soil aggregate stability and the result from redundancy analysis indicated that soil organic carbon?SOC?,Glomu,Paraglomus,Archaeospora explained a significant proportion of the GRSP concentration.The result suggests that the 30 kPa drip irrigation the optimal irrigation amount for use in vegetable production,given that more stable soil structure,more nutrient contents and higher activity of enzymes and AMF were performed while high tomato yields were maintained.