Study On Regulation Of Arbuscular Mycorrhizal Fungi And Biochar On Allelopathy In Continuous Cropping Pear Orchard

In production practice,continuous cropping obstacles have been a problem that plague the efficient production of agriculture,and has occurred in many horticultural plants.Pear is an important economic fruit tree of China.Recently,a number of high-quality early maturing and very early pear varieties have been introduced into Chongqing in large-scale.Due to different regional climatic conditions,lack of arable land and other restrictions,the old pear orchards or nursery grounds need to reuse,which leads to increasingly serious continuous cropping obstacles.Some traditional well-known producing areas are also facing a huge challenge in the variety of structural adjustment and industry promotion.Their technology,market and brand can't be passed on,so the healthy and sustainable development of the pear industry has been seriously constrained.Many studies have confirmed that allelopathy is one of the important factors in continuous cropping obstacles on strawberry,apple,pear and other fruit trees.Therefore,studies on allelopathy in continuous cropping pear orchard can fully reveal the mechanism of continuous cropping obstacles.And the purpose of effectively overcoming continuous cropping obstacles can be achieved by applying the targeted measures.Many studies have found that AM fungi and biochar have great potential in regulation of allelopathy,but research of their combined effect on allelopathy has not been reported.The regulation effect of AM fungi on allelopathy of pear is also rarely studied,and the mechanism is not completely clear.In this study,the growth of two-year-old pear trees planted in the continuous cropping pear orchard and newly built pear orchard at the same time and under the same normal management condition were compared to discuss the relationship between allelopathic autotoxicity and continuous cropping obstacles.The rhizosphere soil was collected from continuous cropping pear orchard and made it into water extracts.Seeds of Pyrus and Bunge were used as experimental material in the biochemical test,which was carried out with the filter paper culture method to verify and evaluate the allelopathic autotoxicity of the water extracts.GC-MS was used to analyze and identify the main species of allelochemicals of the rhizosphere soil.The pot experiment was carried out with materials of one-year-old pear seedlings to study the effect of allelopathic autotoxicity on pear seedlings and regulation effects of AM fungi and biochar.The main conclusions are as follows:1.Compared with the newly built pear orchard,the two-year-old pear seedlings in continuous cropping pear orchard were short,the stem was thin and weak,new shoots grew slowly,and leaf number decreased significantly,continuous cropping obstacles problem was serious.The further study showed that allelopathic autotoxicity i n pear orchard was closely related to its continuous cropping obstacles.2.Results showed that the water extracts had inhibited the seed germination and seedling growth of Pyrus and Bunge in different degrees.Results of allelopathic evaluation showed that the synthetical allelopathic sensitivity of Pyrus seed was higher than that of Bunge seed.3.Alkanes,esters,alcohols,amines,terpenes,phenols,phenols,ketones and aromatic hydrocarbons,9 categories and 77 kinds of chemical components in total,were isolated from the rhizosphere soil from continuous cropping pear orchard by GC-MS.Most of them belong to allelochemicals.The main category was alkanes,accounting for 38.49% of the total composition,followed by esters,alcohols and so on,and the results of previous studies were basically the same.In addition,results found that the allelochemicals mainly present in rhizosphere soil of continuous cropping pear orchard were tetradecane and most alkanes,4-(1,1,3,3-tetramethylbutyl)-phenol,1,2-Benzenedicarboxylic acid,hexadecanoic acid butyl ester,Octadecanoic acid butyl ester,6,10,14-trimethyl-2-pentadecanone and so on,some of them had been confirmed to be active and relevant to plant continuous cropping obstacles.4.The pot experiment showed that water extracts of rhizosphere soil from the continuous cropping pear orchard had significant inhibitory effects on growth of pear seedlings.With the concentration increasing,the inhibitory effect was stronger,which proved allelopathic autotoxicity was an important factor leading to continuous cropping obstacles of pear again.The water extracts can influence the growth of pear seedlings by hindering its development of root system,inhibiting photosynthesis and the antioxidant enzyme activity of leaf,then increasing the accumulation of MDA and aggravating the lipid peroxidation of cell membrane.Content of soluble sugar,soluble protein and proline were changed,cell osmotic balance was destructed,soil available nutrients and enzyme activity were also reduced.5.The study found that inoculated with AM fungi promoted the growth of pear seedlings under the allelopathic stress,directly or indirectly improved the resistance of pear seedlings.Addition of biochar improved the rhizosphere soil environment of pear under the allelopathic stress,and indirectly improved the growth of pear seedlings,thus improved its resistance and relieved damage of allelopathic autotoxicity.Compared with CK,plant height,stem diameter,leaf area,root/shoot ratio,new roots number,root length and activity of pear seedlings were significantly increased when inoculated with AM fungi.Content of leaf chlorophyll was added and the photosynthetic characteristics were improved.Increase of antioxidant enzyme activity of leaf,along with content of MDA and proline decreasing and soluble sugar and protein content increasing at same time,prevented the peroxidation of cell membrane lipid and maintained the internal and external osmotic balance.Furthermore,soil enzyme activity was also increased to a certain extent,then the resistance of plant was enhanced as a whole.Through adding biochar to rhizosphere soil,the soil bulk density was significantly reduced,p H of soil was regulated,and the contents of soil organic matter and available N,P,K catalase,sucrase,neutral phosphatase,protease and urease activity of soil were dramatically increased.So soil available nutrition can be normally supplied to pear seedlings,and indirectly and partly improved its growth,the resistance was increased then.6.The water extracts showed low promotion and high inhibition effect on the infection of AM fungi.Biochar had a gain effect on reproduction and activity of it,the mycorrhizal infection rate(MIR)was significantly improved and mycorrhizal dependency was also enhanced by adding 2% biochar.In comparison with treatment inoculated with AM fungi,MIR was respectively increased by 24.22%,11.64%,14.31% and 5.35% of different water extracts concentration,even when the concentration is 1g·mL-1.Results also showed that combination of AM fungi and biochar had significant synergistic regulative effect on the allelopathic autotoxicity.