Effects Of Flooding And Calcium Cyanamide On Soil In Successive Tea-cuttings Nursery

Tea is a major and monetarily important crop in China.However,the continuous obstacle of tea-cuttings nursery is a common problem in seedling cultivation at present.The main symptoms of continuous obstacles are high fatality rate and low survival rate of seedlings,deterioration of soil physicochemical properties and microbiota in nurseries.Flooding and calcium cyanamide are widely used for the improvement of continuous obstacles and control of soil-borne diseases in facility agriculture,but their applications in successive tea-cuttings nursery are still limited,and the microbial properties that are responsible for the improvement effect have rarely been systematically described.Therefore,in this study,we used flooding and calcium cyanamide to improve the soil conditions of successive tea-cuttings nursery,and investigated 1)the time-series changes of soil physicochemical properties in tea nursery;2)overview of tea seedling biomass and survival rate;3)the response mechanisms of soil fungal,bacterial,and archaeal communities in tea nursery;and explored the physicochemical and microbial mechanisms to improve the survival rate of tea seedlings using field experiments,physicochemical analysis,and high-throughput sequencing techniques.The main results are as follows:1.Flooding and calcium cyanamide ameliorated the acidification of tea-cuttings nursery.The acidification trend slowed down with time accumulation.Calcium cyanamide application reduced total polyphenols,bound polyphenols and soluble aluminum contents.Flooding and calcium cyanamide promoted the biomass and survival rate of tea seedlings.2.Through the analysis of microbial community construction,it was found that microbial community construction was driven by environmental factors and that environmental variables could explain a large proportion of microbial community variation.Among them,TN,SOC,BP and NH₄⁺-N were the key environmental factors affecting fungal community;AP,AK,pH and NO₃^--N were the key environmental factors affecting bacterial community;SOC,pH,TP,Ex-Al,BP and TN were the key environmental factors affecting archaeal community.3.The distribution patterns of fungal community and the abundant taxa in bacterial community were relatively similar.Flooding with calcium cyanamide reduced the complexity and connectivity of the network,but also increased the modularity thus increasing the resistance to external changes.What's more,pathogen-resistant related taxa in fungal communities were more often identified as key taxa in the calcium cyanamide group,while key taxa in control group were more identified as pathogenic fungi.The pattern of change in the rare taxa network of the bacterial community was reversed,as calcium cyanamide application resulted in a more stable and complex network compared to the control group,thereby enhancing interactions between the bacterial groups.The functions of most of the key taxa in the bacterial network were related to the degradation and metabolism of nutrients such as carbon,nitrogen and phosphorus.Furthermore,the application of calcium cyanamide allowed bacteria(Bryobacter)associated with resistance to root-knot nematode disease to occupy a more dominant ecological niche.4.Microbial community in the soil of tea-cutting nursery exhibited functional diversity.Among the fungal communities,the saprotroph was the dominant trophic mode.In the bacterial and archaeal communities,metabolism is the dominant function.The microbial community contains huge taxonomic and functional diversity,and saprotroph and microbial metabolism have important effects on the physiological and biochemical processes of tea seedlings.In summary,flooding with calcium cyanamide treatment can be recommended as a method used in production practice to improve successive tea-cutting nurseries.This treatment can effectively improve the problems of low pH,polyphenol accumulation and aluminum toxicity in continuous nursery.It can increase the soil nutrient content and the utilization of plant nutrients;kill plant pathogens in fungal community,reduce the richness of fungal community,increase the richness and diversity of bacterial and archaeal communities,induce the transformation of continuous nursery soil from fungal-dominated to bacterial-dominated,regulate and improve the structural balance of microflora,and affect the microorganism co-occurrence pattern and community function,thus improve the soil physicochemical and microbial conditions,promote the successive-cutting nursery to obtain higher survival rate.