Effects Of AMF And Rhizobium On Nutrient Absorption And Rhizospheric Microecological Characteristics Of Intercropped Fortunella Margarita

As one of the main producing areas of Fortunella margarita,29.9%of the total area of Guangxi is karst landform.It has characteristics of relatively infertile soil and frequent seasonal drought as well as the low current seasonal utilization rate of fertilizer.All of the mentioned above reasons restrict the development of Fortunella margarita industry.Thus in this study,arbuscular mycorrhizal fungi?AMF?--Claroideoglomus etunicatum?C.e?and rhizobium?R?--Bradyrhizobium japonicum?B.j?were inoculated with kumquat?Fortunella margarita?and soybean?Glycine max?intercropping system.A total of 9 treatments were designed as listed below:?1?monoculture Fortunella margarita,abbreviated as?later it is abbreviated with a colon‘:'?F;?2?monoculture soybean:S;?3?Fortunella margarita inoculated with AMF:F+A;?4?soybean inoculated with AMF:S+A;?5?soybean inoculated with R:S+R;?6?Fortunella margarita intercropped soybean:F+S;?7?Fortunella margarita intercropped soybean inoculated with AMF:F+S+A;?8?Fortunella margarita intercropped soybean inoculated with R:F+S+R;?9?Fortunella margarita intercropped soybean inoculated with both AMF and R:F+S+A+R.Among them,treatment 1-5 were monoculture group and treatment 6-9 were intercropping group.This study expored the effects of the above treatments on the micro-ecological characteristics such as the bacteria and fungi community structure changes of Fortunella margarita rhizospheric soil,the nutrient absorption related growth and metabolism of Fortunella margarita seedling,and the potential mechanisms,to conducted to provide a theoretical basis on high-efficiency,cost-effective and high-yielding Fortunella margarita production.The main results are as follows:1.The mycorrhizal infection intensity in root system of Fortunella margarita grafted seedlings?M%?of F+A treatment was the highest,which was significantly higher than other treatments?p<0.05,the same as below?,F+S+A+R and F+S+A treatment were the second and third highest.The dry weight and number of soybean root nodule per plant in the Fortunella margarita soybean intercropping group were significantly lower than that of the corresponding monoculture soybean treatment group in which the nodule dry weight and number of F+S+A+R treatment were the highest in the intercropping treatment group,there was no significant difference among the monoculture crop treatment group?p>0.05,the same as below?.The results showed that AMF and rhizobium developed well and could promote mutually.2.The invertase?0.48 mg/g?and phosphatase?0.19 mg/g?activities of Fortunella margarita rhizospheric soil of the F+S+A treatment were the highest,while the urease activity?19.70 mg/kg?of the F+S+R treatment was the highest,all of them were significantly higher than those without inoculation treatments?including F or F+S treatment,the same as below?.Compared with the non-inoculation treatments,regardless of intercropping or not,the organic matter mass fraction?O.M?of the Fortunella margarita rhizospheric soil of the 3 inoculated treatments?including F+S+A,F+S+R and F+S+A+R treatments?were significantly increased by more than 20.02%,and the differences between inoculated treatments were not significant;the change of soil total nitrogen content?TN?also showed a similar trend.The soil total phosphorus content?TP?of F+S+A treatment was highest?1.175 g/kg?;the soil available phosphorus content?AP?of F+S+A+R treatment was the highest?21.684 mg/kg?,which was significantly higher than the other treatments;the N and P absorbents of Fortunella margarita of F+S+A treatment were both the highest(1246.36 and 167.97 kg·hm^-2,respectively),followed by F+S+R treatment,which was significantly higher than those of F treatment.The soil total potassium content?TK?of F+A and F+S+A+R treatment were both the highest,there was no significant difference between the two treatments;And the soil available potassium content?AK?of F+S+A treatment was highest,which was significantly higher than the non-inoculated treatments.It was suggested that treatments with AMF had the best effects on the soil N,P and K content of Fortunella margarita rhizosphere in intercropping system,followed by that with rhizobium.3.The increasement effect of AMF on the soil bacterial OTU number of Fortunella margarita rhizosphere was relatively the largest,and the increasement effect of the Rhizobium on the soil fungal OTU number was relatively largest.Compared with F treatment,the proportion of soil Proteobacteria and Bacteroidetes of other treatments all increased,and only the proportion of Acidobacteria reduced.the proportion of Candidatus_Koribacter,nitrospira,Rhodoplanes,etc.of most of the remaining treatments increased,the proportion of Candidatus_Solibacter reduced.Among them,the increasingeffects of proportion of the bacterial phylum and the genus of F+S+A treatment were relatively largest.The predominant phylums of fungi in all treatments were Ascomycota,Basidiomycota,and Zygomycota,the identified genuses were Mortierella,Geminibasidium,Fusarium,Chloridium,etc.Compared with the F treatment,the phylum and genus proportion of the fungal with inoculated treatments showed high or lowchange,Among them,the effect of F+S+A+R treatment was relatively larger.4.Compared with the F treatment,increased the chao,ace?representing species richness?and Shannon?representing Alpha diversity of microbial community?indexes of Fortunella margarita rhizospheric soil bacteria and fungi of the other treatments increased in varying degree,and only F+S+R treatment in the intercropping group was significantly different from F treatment,and the second highest was that of F+S+A treatment.According to the Beta heat map analysis,the Beta diversity of the bacterial community of the Fortunella margarita rhizospheric soil treated with F+S+A,and the Beta diversity of the fungal community treated with F+S+R were relatively higher than those of the F treatment.5.In the intercropping group,the soil microbial biomass C?B_C?value of Fortunella margarita rhizosphere treated with F+S+A+R was the highest,but there was no significant difference from the treatment of F+S;the soil microbial biomass N?B_N?value of the F+S+A treatment was the highest?84.32 mg/kg?,which was significantly higher than that of other treatments.It can be seen that the increase effect of AMF on soil microbial biomass was relatively significant.After inoculation with AMF,the number of inorganic P-resolving bacteria increased,and that of the treatment of F+S+A+R was the highest.Compared with the treatment of F+S,the number of aerobic autotrophic N bacteria of the intercropping and inoculation treatments increased and that of the anaerobic autogenous N bacteria reduced,the difference were not significant.6.The root vitality of Fortunella margarita treated with F+S+A was the highest,but there was no significant difference from the treatments without inoculation,indicating that inoculation with AMF increased the root vitality of Fortunella margarita to a certain extent.The total chlorophyll content of Fortunella margarita leaves treated with F+S+R was the highest?1.2140 mg/g?,and the net photosynthetic rate of F+S+A treatment was the highest(12.63?mol CO₂ m^-2s^-1),which was significantly higher than that of F treatment;the total sugar content of the three Fortunella margarita intercropped and inoculation treatments were significantly higher than that of the F treatment,but there were no significant difference between the three intercropped treatments.The dry weight?189.705 g/plant?and plant height?97.72cm/plant?of Fortunella margarita treated with F+S+A were the largest,which was significantly higher than that of F treatment.In summary,in the Fortunella margarita soybean intercropping system,AMF and Rhizobium can mutually promote each other,and improve the plant rhizospheric microenvironment by increasing the content of soil C,N and P and other nutrients in the Fortunella margarita rhizosphere,and affecting the soil microbial community structure,promoting the nutrition of Fortunella margarita absorption and growth,Among them,F+S+A treatment of Fortunella margarita represent the best growth promotion effects.