| There are many problems in citrus production,such as the slow growth of plants in the south of China.As a modern orchard soil management model,orchard grass cultivation is gradually emerging in fruit production.The development of orchard grass production technology has become a multi-disciplinary interdisciplinary field,and the main research direction is focused on the orchard grass production management mode in the aspects of orchard soil micro environment regulation(enzyme activity and microbial content),improving orchard soil nutrient content,fruit quality,strengthening tree vigor,etc.Arbuscular mycorrhizal fungi(AMF)coexist with citrus root system to promote the growth of citrus,while legumes are often used as orchard grasses,which can store water and conserve water.AMF is lack of host specificity.It can form hyphal connection between different plant roots and mediate nutrient exchange between intercropping plants and production crops.How to utilize the interaction between rhizobia and AMF to achieve good ecological effect through the two-way symbiosis of the grass crops and the roots of fruit trees in the orchard is rarely reported.To study the symbiosis of AMF with white clover and citrus root system,intercropping and inoculation of AMF can increase the nitrogen fixation capacity of legumes and improve the soil nitrogen nutrient,but the interaction mechanism is not clear.Therefore,it is necessary to explore the interaction mechanism of AMF and Rhizobia on citrus growth and nitrogen fixation of clover,which is of great significance to reduce the use of chemical fertilizers,pesticides,especially herbicides.In this experiment,the dominant species of AMF in citrus are Funneliformis mosseae(F.m)and Glomus intraradices(G.i)as inoculants,the annual potted RedRiver orange seedlings as test plants,the intercropped legumes as white clover,and the inoculated rhizobia as white clover.Under the interaction of AMF and rhizobia,the effects of three leaf grass development and citrus seedling growth,citrus physiological metabolism and element regulation,citrus rhizosphere soil properties and microenvironment,and the molecular mechanism of nitrogen fixation of three leaf grass were studied.The mechanism of promoting orange growth and nitrogen fixation of three leaf grass by AMF under white three leaf intercropping was analyzed comprehensively.The main results are as follows:1.G.i and F.m can infect white clover root system and citrus seedling root system very well.The infection rate of white clover root mycorrhiza can reach 35.98% and47.45% respectively.Inoculation of white clover with Rhizobium can effectively improve the infection rate of AMF in Citrus seedling root system.The infection rate of G.i and F.m mycorrhiza can increase 12.64% and 13.98% respectively.The interaction between rhizobia and AMF increased the biomass of Trifolium repens,the number and weight of nodule in rhizosphere,and the activity of nodase.2.Planting grass and inoculating AMF can effectively increase the biomass of citrus and enhance the growth and development of root system of citrus seedlings.Compared with the treatment only inoculated with AMF,the growth of citrus seedlings inoculated with AMF and intercropped with clover was better.Compared with FM treatment,the root volume,root activity,the number of first-class new roots and the longest lateral root length in FM + R increased by 26.99%,28.26%,26.58% and 7.71%,respectively.The growth of grass and AMF can also increase the photosynthetic rate and the efficiency of carbon assimilation in citrus.The total inoculation of F.m is better than that of G.i.3.At the early stage of 180 days after treatment,compared with the later stage of240 days after treatment,the content of soluble sugar / protein and the activity of sucrose synthetase(SS)in citrus seedlings increased more in the grass planting and AMF inoculation treatment,which indicated that the interaction effect promoted the accumulation of sugar,protein and other substances more effectively in the early stage.However,the activities of catalase(CAT)and peroxidase(POD)increased in the middle and late stage of citrus seedlings,and the accumulation of total N,nitrate N,total P,total K,and total C also increased,which indicated that the interaction of rhizobia and AMF enhanced the response ability of citrus to adversity and the absorption of elements.Compared with CK without AMF,only AMF can enhance theefficiency of element regulation and physiological metabolism of citrus seedlings,while AMF and AMF can form hyphal connection,which is better than only AMF.4.Compared with the treatment of AMF only,the number of all kinds of soil microorganisms such as nitrogen fixing bacteria and ammoniating bacteria,urease and nitrogen fixing enzyme activities in the soil,and the content of GRSP in the rhizosphere soil of citrus seedlings increased significantly in the treatment of AMF and grass planting.The results showed that the interaction between AMF(F.m and G.i)and rhizobia could improve the soil,promote the reproduction of soil beneficial bacteria,enhance the fixation ability of soil nitrogenase to nitrogen and other elements,and increase the available nutrients in the soil.5.Compared with CK + R,the expression of nif-H,nif-D and nif-K genes,which are the key genes in nodule nitrogenase synthesis,increased significantly at the transcription level.The expression of nif-H gene increased by 48.76% and 36.36%,and the expression of nif-d gene increased by 31.98% and 57.81%,respectively.The expression of nif-D gene increased by 83.54% and 92.95%,respectively.The results showed that AMF could increase the rate of nitrogenase synthesis and the ability of nitrogen fixation of roots.The effects of AMF on the expression of nitrogenase related genes were different.For the expression of nif-H gene,G.i > F.m,for the expression of nif-D and nif-K gene,F.m > G.i.The results showed that the inoculation of G.i was beneficial to the synthesis of ferritin,while the inoculation of F.m was beneficial to the synthesis of ferromolybdenum.The improvement degree of F.m.inoculation was more significant,which was positively related to the infection degree of AMF in the root system of clover. |
PDF Full Text Request