| Citrus is one of the most important economic crop in agricultural industry in China,and it is also an important economic pillar in southern China.With the rapid growth of citrus planting area and output,the focus of the citrus industry has gradually shifted to pollution-free fruit production and labor-saving cultivation.As a modern management model of orchards,grass cultivation is gradually emerging in citrus production and Trifolium repens L.is considered to be a better intercropping grass species,but the allelopathic effect and mechanism of Trifolium repens L.on citrus have not systematic research.Root exudates are not only the main source of plant-derived allelochemicals,but also the key cause of continuous cropping obstacles,autotoxicity,and stubble in agricultural production.The interaction between plant-soil-microbes mediated by root exudates has become a key issue in modern horticulture and other disciplines.The mycorrhizal structure formed by arbuscular mycorrhiza fungi（AMF）and citrus roots has excellent growth-promoting effect on plants and is widely used in orchard production.However,there are few reports on its regulatory effect in allelopathy.With the expansion of the promotion and application of the citrus/Trifolium repens L.intercropping model,exploring the allelopathic effect and mechanism of Trifolium repens L.root exudates on citrus,and clarifying the potential regulatory effect of AMF in the allelopathic effect can be used for the selection of scientific planting models,and provides a theoretical basis for the development of new biological pesticides.In this experiment,the components of Trifolium repens L.root exudates and its allelopathic effects and characteristics on citrus were preliminarily determined by GC-MS technology and indoor bioassay.On this basis,a greenhouse pot experiment was set up,and the common AMF dominant strain Funneliformis mosseae（denoted as F.m）was used as the inoculant.Two cases of uninoculated（NAM）and inoculated AMF（Fm）were set to explore the treatment of Trifolium repens L.root exudates with different concentration gradients(0,0.01g·m L-1,0.02g·m L-1,0.05g·m L-1).Comprehensive analysis of the effects on physiological indicators such as citrus growth and development,AMF symbiosis efficiency,protective enzyme system,osmotic adjustment substances,and endogenous hormone levels,as well as on ecological indicators such as the number,structure,activity of rhizosphere soil microbial community,and soil key enzyme activities.The allelopathic effects and characteristics of Trifolium repens L.root exudates on citrus,and the potential regulatory effects of AMF inoculation on allelopathic effects.The main conclusions are as follows:1.Through GC-MS identification and analysis,39,52 and 58 compounds were identified in the root exudates of Trifolium repens L.in n-butanol,petroleum ether and ethyl acetate,respectively,belonging to aldehydes,esters,ketones,phenols,alcohols,alkanes,alkenes,aromatic hydrocarbons,acids,glycosides,amino acids,amides,etc.,indicated that the root exudates of Trifolium repens L.contain a variety of potential allelochemicals,among which 4,6-ditert-butyl-2-（4-hydroxybenzylidenamino）-Phenol,Dibutyl phthalate,2,4-Di-tert-butylphenol,Phthaloylaspartic acid and other substances had high content.2.The root exudates of Trifolium repens L.had allelopathic effects on citrus seed germination and seedling growth and development.Various concentrations of Trifolium repens L.root exudates had a general inhibitory effect on the germination of citrus seeds,while the physiological activity indicators such as the growth and development of citrus seedlings and antioxidant enzyme activities showed an overall trend of"low concentration promotes high concentration inhibition",indicating that the allelopathy had a selection effect and a concentration effect.3.The root exudates of Trifolium repens L.and inoculation of AMF with appropriate concentration could effectively promote the growth of citrus seedlings above ground and root development.Appropriate concentration of Trifolium repens L.root exudates can increase the infection rate and symbiosis efficiency of AMF on the roots of citrus seedlings,and improve the process of plant photosynthesis,but when the concentration of Trifolium repens L.root exudates is too high(0.05 g·m L-1),it could significantly inhibit the root vitality which could cause stress damage to citrus seedlings and then inhibit the normal growth and development of plants.AMF inoculation can alleviate the stress damage caused by high concentration of allelopathic stress to a certain extent.4.Pot experiment showed that the root exudates of Trifolium repens L.could affect the activities of antioxidant enzymes and the content of osmotic regulators in various parts of citrus seedlings.Low concentrations of Trifolium repens L.root exudates(0.01,0.02 g·m L-1)continuously accumulated peroxides such as MDA in plant tissues,induced and activated the activities of SOD,POD,CAT,APX and other antioxidant enzymes in leaves and roots of citrus seedlings.Increased the content of osmotic adjustment substances such as free proline,soluble sugar,and soluble protein to improve the ability of plants to resist stress.The allelopathic stress of high concentration of Trifolium repens L.root exudates(0.05 g·m L-1)aggravated the oxidative damage of citrus seedlings and hindered their growth and development.Inoculation of AMF could enhance the tolerance and resistance of citrus seedlings to high concentrations of Trifolium repens L.root exudates,effectively alleviate the damage of high concentrations of allelopathic stress,and increase the concentration threshold of Trifolium repens L.root exudates.5.Trifolium repens L.root exudates could affect the accumulation of endogenous hormones such as ABA,IAA,GAs and ZR in the leaves and roots of citrus seedlings,and change the proportional balance between the hormones,thereby affecting the growth and development of plants.Trifolium repens L.root exudates significantly increased the ABA content of citrus seedlings to improve stress resistance.Low concentration treatments(0.01,0.02 g·m L-1)could increase the accumulation of IAA,GAs and ZR in tissues to a certain extent and promote plant growth,ABA significantly increased under high concentration treatment(0.05 g·m L-1),while the accumulation of IAA,GAs,ZR and other growth-promoting hormones decreased significantly,which inhibited plant growth and development.Inoculation of AMF could increase the content of ABA,IAA and GAs in tissues and maintain normal plant growth,but the effect was not obvious under the treatment of Trifolium repens L.root exudates.6.Both Trifolium repens L.root exudates and inoculation with AMF could increase the number of microorganisms in the rhizosphere soil of citrus seedlings to a certain extent,and change the composition of the microbial community in the rhizosphere soil of citrus.The induction effect of Trifolium repens L.root exudates on rhizosphere soil flora was stronger than that of AMF.Appropriate concentrations of Trifolium repens L.root exudates and inoculation of AMF can increase the activities of urease,polyphenol oxidase,peroxidase and other soil enzymes in the soil,and improve the rhizosphere soil environment of plants,too high concentration(0.05 g·m L-1)has inhibitory effect on soil catalase and peroxidase activities. |
PDF Full Text Request