| The cotton planting mode is perennial continuous cropping accompanied by straw returning in Xinjiang.The straw returning can not only provide sufficient nutrients and energy for soil microorganisms,but also improve microbial activity and community structure,which is the main way of soil organic fertilizer cultivation in oasis cotton fields.As a marker of microbial residues in soil,amino sugars are used to evaluate the accumulation of soil organic matter and nutrient transformation by microorganisms.Therefore,the study on the accumulation and composition characteristics of amino sugars in long-term continuous cropping cotton soil is aimed at evaluating the microbial transformation process and activation mechanism of soil nutrients in cotton field under long-term continuous cropping and straw return.Based on continuous cropping experiment of cotton,the contents of glucosamine,galactosamine and muramic acid in the three soil layers of cotton soil in different continuous cropping years and 9-year continuous cropping aggregates were determined by high performance liquid chromatography,to study the accumulation characteristics of amino sugars in the soil of cotton field under long-term continuous cropping and straw return.Reveal the transformation mechanism of soil microorganisms in continuous cropping cotton fields in Xinjiang oasis.The main research results are as follows:1.The contents of total nitrogen,organic carbon,total phosphorus and total potassium in the soil of long-term continuous cropping cotton field have increased significantly,and they gradually accumulated with the increase of cotton continuous cropping years.The overall performance was as follows:29a>24a>19a>14a>9a,which reached the highest value was 713.17 mg·kg-1,15.89 g·kg-1,1.08 g·kg-1,23.17g·kg-1 in 29 years of continuous cropping,respectively,which was 40.23%,25.22%,24.14%and 27.66%higher than that of 9a treatment.Soil nitrate nitrogen and ammonium nitrogen contents varied from5.86～9.83 mg·kg-1 and 4.98～7.35 mg·kg-1,respectively,and showed a significant increasing trend with the increase of cotton continuous cropping years,and the highest was at 29 years.However,soil C/N was relatively stable and showed no significant difference between successive cropping years.2.The contents of total amino sugars and amino monosaccharide in the long-term continuous cropping cotton soil increased significantly,and with the continuous cropping years of cotton,the content of total amino sugars,glucosamine and galactosamine in the soil all showed a gradual increase trend.In 29 years,its contents were:150.43～178.18 mg·kg-1,104.29～124.95 mg·kg-1,40.60～47.64 mg·kg-1,and compared with 9 years,it increased by 25.03%～99.85%,20.01%～91.85%,48.92%～145.32%;while the muramic acid content first decreased and then increased,reaching the highest value at 29a within 10～30cm of the soil layer,respectively:6.26 mg·kg-1,5.55 mg·kg-1.Among them,the accumulation of glucosamine is the most obvious advantage,accounting for 70.43%～71.14%of the total amino sugars.In the soil layer with a depth of 0～30 cm,the contents of total amino sugars and three kinds of amino monosaccharides decreased with the increase of soil depth,and the content of 0～10 cm soil layer is the largest.The value of Glu N/Mur A in the soil shows an overall increasing trend with the increase of the continuous cropping years of the cotton field,which has a great influence on the soil layer of 0～20 cm.And in the three soil layers with a depth of0～30cm,29a is 39.66%,25.02%and 50.96%higher than 9a respectively.3.The content of amino sugars in different aggregates in the three soil layers of 0～10 cm,10～20 cm and 20～30 cm in cotton continuous cropping for 9 years changed significantly.The contents of total amino sugars(104.18～166.02 mg·kg-1),glucosamine(73.59～122.26 mg·kg-1),galactosamine(26.43～37.19mg·kg-1)and muramic acid(4.06～6.56 mg·kg-1)changed basically the same,which increased with the increase of soil aggregate particle size.The contents of total amino sugars and three monosaccharides were all increased in large aggregates（>2000μm）was the highest content,respectively:166.02 mg·kg-1,122.26mg·kg-1,37.19 mg·kg-1,and 6.56 mg·kg-1;Moreover,in the three soil layers,its content decreased gradually with the deepening of soil depth,and the highest content was found in the surface layer of 0～10cm.Conclusion:Long-term continuous cropping of cotton with straw returning can increase soil organic carbon,nitrogen and nutrient contents,improve soil quality and stability,and promote the accumulation of amino sugars and three kinds of amino monosaccharides in the soil.Continuous cropping increased the relative contribution of fungal microbial residues represented by glucosamine,which led to the transformation of organic matter in the soil into a dominant fungal community,and thus improved soil microbial activity and organic matter conversion and accumulation capacity. |
