Effect And Mechanism Of Xanthan Gum Composite Water Retaining Agent On The Growth And Development Of "Yunyan 87"

Tobacco(Nicotiana tabacum L.)is one of the main cash crops in some parts of China,and its cultivation is very widespread.The production and cultivation of high-quality tobacco is limited by many factors.At present,the cultivation method of tobacco leaf production in China generally uses the nutrient soil combined with the secondary burrowing method,which can promote the early growth and rapid onset of tobacco roots,but it also has the disadvantages of easy disease,high labor intensity,long production cycle,and inability to adapt to mechanized operations.Water retaining agent can promote tobacco growth and development,improve soil properties,regulate microorganisms,and have broad application prospects.In this study,the effects of the compound water retaining agent on the agronomic traits,leaf physiological indexes,root physiological activities,soil physicochemical characteristics and rhizosphere microbial communities of flue-cured tobacco were studied by mathematical statistical analysis,and the effect of different cultivation systems in the whole growth period of tobacco was comprehensively evaluated by factor analysis,and soil microorganisms were further screened to degrade xanthan gum,which proved that it was environmentally friendly,and the physiological activity of its degradation products was studied.The main findings are as follows:1.Study the effects of different concentrations of xanthan gum on the physiology and biochemistry of tobacco seedlings under drought stress.After 500 ～ 2500 mg/L xanthan gum was applied to tobacco soil and subjected to drought stress for 8 days,it was found that the tobacco seedlings treated with 2000 mg/L xanthan gum were closest to those under normal growth conditions in terms of physiological characteristics,phenotype and chlorophyll fluorescence characteristics,which had a significant effect of alleviating drought stress.2.When exploring the effects of compound water retention agent on the growth and development and root growth of tobacco plants at different growth stages,2000 mg/L xanthan gum and 500～2000 mg/L potassium fulvic acid were combined and compared with traditional nutrient soil.The results showed that the application of composite water retention agent could significantly reduce the content of malondialdehyde in leaves,keep the activities of catalase and superoxide dismutase in equilibrium,and enhance photosynthesis in leaves.At the same time,the use of composite water retaining agent can also promote the thicker stem of tobacco plant,effectively increase the number of leaves and leaf area of tobacco plant,promote the development of root system and improve its vitality,thereby reducing the root-to-head ratio and increasing the accumulation of dry matter of tobacco plant.3.When studying the effects of composite water retaining agent on the physicochemical characteristics and microbial diversity of tobacco soil at different growth stages,it was found that compared with traditional nutrient soil,composite water retaining agent has a positive effect on the physical and chemical properties of soil,which can improve soil moisture content,reduce soil bulk density,effectively alleviate soil acidification,promote the utilization rate of alkaline hydrolyzable nitrogen and available potassium,and enhance organic matter content.At the same time,the use of composite water retention agents increased the activities of urease,sucrase,cellulase,dehydrogenase,catalase and polyphenol oxidase in soil during different growth periods,and effectively enhanced the utilization of soil fertilizer efficiency.The increase in the abundance of beneficial bacterial groups,such as actinomycetes,proteobacteria,arthrobacterium,bacillus,and lysobacteriacetes,was associated with the above changes in soil properties,but the phylum Acidobacteriacetes and Phylum Chlorella were strongly inhibited under this condition.The fungal diversity results showed that the contents of available potassium,available phosphorus,sucrase and urease were negatively correlated with the growth of ascomycete phylum and basidiomycetes,which fully inhibited the incidence of root rot and stem rot.In addition,the composite water retention agent plays an important role in improving the activities of polyphenol oxidase,dehydrogenase,cellulase and sucrase,increasing soil organic matter,effective phosphorus content,reducing soil acidity,promoting the enrichment of Penicillium,and inhibiting the pathogenic Fusarium.Combined with redundancy analysis,effective nitrogen,phosphorus and potassium were the main drivers of bacterial communities.p H,available potassium and available phosphorus were important environmental variables affecting the structure of fungal communities.In order to verify the environmental protection of xanthan gum,a strain of xanthan gum-degrading bacteria(Bosea robiniae strain XJ5)was screened for the screening of xanthan gum-degrading bacteria and the biological activity of oligosaccharide products.The bacteria can efficiently degrade xanthan gum to water samples and produce xanthan gum oligosaccharides.Through in-depth exploration,it was found that this oligosaccharide product can effectively scavenge hydroxyl radicals and has the ability to activate the plant defense system.4.Under the observation conditions of the whole growth period,different cultivation systems affected the comprehensive evaluation of tobacco.The principal factor modeling synthesized the four key quantities of tobacco plant growth,agronomic traits,physiological indexes,and soil fertility of tobacco planting.Using the dataset of 3 growth periods,6principal factors were obtained after factor analysis.After comprehensive calculation and sorting of the main factor scores,the results showed that T2>T3>T1>Y>CK,indicating the optimal effect of applying 2000 mg/L xanthan gum + 1000 mg/L potassium fulvic acid and its feasibility of replacing nutrient soil for actual production.The results of this study provide a solid theoretical basis for the application of xanthan gum composite water retaining agent instead of nutrient soil in production,and have important reference significance in ecological environmental protection,sustainable tillage of tobacco fields,labor reduction and cost reduction,mechanization of tobacco leaf production,and cultivation technology innovation.