| According to statistics,the area of protected horticulture in China has reached 3.7 million hm2 in 2017,accounting for about 80%of the world’s facility cultivation area,and has become the country with the largest facility cultivation area in the world.With the progress of agricultural science and technology,the production of protected crops is gradually developing towards the direction of soilless,therefore,a large number of organic substrates are needed for soilless cultivation of crops.In most cases,these organic substrates are discarded after producing only one crop,resulting in a large number of used organic substrates.The improvement and reuse of waste substrates can greatly reduce labor input,production cost,stacking site and environmental pollution.However,there is currently no economical and reliable way to reuse the used substrate except for disinfection.Therefore,it is of great significance to seek an economical and reliable way to utilize the waste substrate which can improve the activity of the waste substrate itself.Arbuscular mycorrhizal fungi,an important part of the terrestrial ecosystem,is a ubiquitous soil microorganism and obligate symbiosis,and can form a mutually beneficial symbiotic relationship with the roots of about 80%of vascular plants.In view of the advantages of AMF in promoting crop growth,improving resistance and promoting nutrient absorption and many other aspects,and combined with the large amount of waste organic substrate to be reused in soilless cultivation in China,we speculate that AMF plays an important role in improving the properties of waste organic substrate and promoting crop growth.In this study,tomato,rice,watermelon,and tulips were used as materials to study the effect of AMF(Funneliformis mosseae,F.m)on promoting crop growth in continuous cropping substrate,and tomato was used to study the mechanism of AMF promoting the growth of crops in continuous cropping substrate.The main findings are as follows:1.AMF significantly increased the plant height,stem thickness,fresh and dry weights of tomato and watermelon seedlings in the continuous cropping substrate;AMF significantly promoted the plant height,leaf age,stem base width,shoot dry weight,root dry weight,root number per plant and longest root length of rice seedlings in the continuous cropping substrate.The results showed that AMF can improve the growth of tomato,rice,watermelon and tulip crops in continuous cropping substrate,and the addition of AMF may be an effective way to realize the reuse of waste substrates.2.AMF significantly improved root development and morphological structure of tomato seedlings in continuous cropping substrate,and significantly increased root activity and NADP-malic enzyme(NADP-ME)activity.Root transcriptome analysis showed that the plant hormone signal transduction pathway was relatively enriched,and 109 genes positively correlated with AMF plant phenotype were obtained through gene set enrichment analysis(GSEA),among which 9 genes were correlated with IAA.The analysis of endogenous hormones showed that the endogenous IAA level of tomato seedling roots was significantly increased after AMF infection.In order to further prove the effect of the increase of IAA content induced by AMF on the root activity and seedling growth,we irrigated IAA and TIBA-a synthesis inhibitor of IAA in the roots of tomato seedlings cultivated in continuous cropping substrate and continuous cropping substrate with AMF at 30 days of seedling age,and studied the relationship between IAA and tomato root activity and NADP-MEs.The results showed that IAA significantly increased the expression levels of NADP-ME1 and NADP-ME2,as well as NADP-ME activity,and enhanced seedling root activity.Therefore,AMF enhanced the NADP-ME activity and root activity of tomato roots by enhancing the expression of NADP-MEs mediated by IAA,so as to promote the growth of tomato seedlings in continuous cropping substrate.The results provide useful information for the reuse of waste substrate by AMF. |
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