| To explore the way to overcome citrus yellowing in calcareous soil,experiment consists of three treatments,A:conventional fertilization（CK）;B:conventional fertilization+medium and trace element fertilizer;C:conventional fertilization+medium and trace element fertiliz-er+bio-organic fertilizer,were designed.Experiments were conducted to study the effect of different treatments on leaf nutrition and soil fertility at different growth stage.The soil mi-crobial communities of different treatments were analyzed by Illumina Miseq sequencing technique.The main results were as follows:At different stages of citrus growth,treatment C significantly increased chlorophyll content in citrus leaves compared with other treatments,especially in the early stage of fruit expan-sion（July）.The chlorophyll content in the citrus leaves of treatment C was significantly in-creased by 319.25%and 59.08%,compared with control and treatment B.The activities of CAT and POD of citrus leaves were effectively increased by C treatment in different growth stages of citrus Compared with other treatments.The activity of CAT and POD reached the highest under C treatment,which were 443.48 mg H2O2?g-1?min-1 and19207U/min-1?g-11 FW in the budding stage（March）.Compared with CK,the Fe content in citrus leaves of treatment C increased by 19.20%-47.02%at the fruit stabilization stage（May）,the early stage of fruit expansion（July）and the late stage of fruit expansion（September）;and the Zn content in citrus leaves increased by1.86%-29.30%at the budding stage（March）and in the period of fruit stabilization（May）;and the Mg content in citrus leaves increased 37.50%at the budding stage（March）.Treatment B and C significantly increased the soil nutrient content and the enzyme activity,and the effect of treatment C reached the highest.Comparison to control,the content of soil organic matter,A-P and A-K increased by 11.41%-51.19%,96.22%-171.84%,5.67%-47.11%;and sucrase activity,alkaline phosphatase activity,catalase activity and urease activity in-creased by 44.29%-141.34%,21.43%-62.50%,4.11%-13.33%,5.82%-29.39%at different growth periods of the citrus.Compared with the control and treatment B,treatment C effectively increased the content of soil available Fe,Zn and exchangeable Mg at different growth stages.The trends of content of available Fe and available Zn in different treatments increased firstly（from budding stage to early stage of fruit expansion）and then decreased（late stage of fruit expansion）.However,the content of soil exchangeable Mg changed unregularly.Treatment C could effectively increase the number of soil bacteria and actinomycetes,and decrease the number of soil fungi in citrus rhizosphere.During the whole growth cycle of cit-rus,the number of soil bacteria,fungi and actinomycetes increased at early germination to germination)and then decreased（from budding to fruiting）and then increased（after fruit sta-bilization）under different fertilization treatments.Miseq sequencing results showed that,at the 97%level,a total of 104158 OTUs of soil bacteria were obtained from two samples collected in March（germination period）and in September（the late stage of fruit expansion）,which were divided into 41 phylum,including132 classes,282 orders,469 families,837 genera.Fertilization changed the relative abu n-dance of dominant bacteria at the phylum level.Compared with the control,treatments B and C had higher relative abundance in Actinobacteria and Chloroflexi.The relative abundance of Proteobacteria and Actinobacteria were significantly different between the two growth stages.Compared with control and treatment B,treatment C significantly increased the abundance of Pseudomonas and decreased the relative abundance of Nitrospira and Haliangium.The rela-tive abundance of Pseudomonas and Cupriavidus were significantly different between the two growth stages.The RDA results showed that Soil pH,available K,organic matter,urease and catalase ac-tivities were the main environmental factors affecting the soil bacterial communities. |
