Study On The Mechanism Of Roasted Tobacco-maize Relay Intercropping Promotes Tobacco Maturity

Roasted tobacco is one of the important cash crops,but the long-term monoculture leads to the reduction of soil nutrient supply,which affects the normal growth of tobacco plants.Crop combination is one of the important cropping methods,but there are unclear studies on the mechanism of how roasted tobacco-maize relay intercropping combination improves soil nutrient supply and its soil microbial community diversity to promote roasted tobacco maturation.Based on this,this experiment used Honghuadajinyuan and K326 as test materials,considering two factors of roasted tobacco varieties and planting methods,i.e.,Honghuadajinyuan mono-crop（HMC）,Honghuadajinyuan overcrop maize（HIC）,K326 mono-crop（KMC）,K326 overcrop maize（KIC）.The soil culture experiment was conducted to investigate the effects of the two crops on soil nutrient supply and soil microbial community diversity,and to further investigate the mechanism of roasted tobacco-maize relay intercropping to promote the maturation of tobacco plants through the changes of exogenous plant hormones on the growth of tobacco plants and soil microenvironment:1.The effects of different varieties of roasted tobacco crop with maize on the growth of roasted tobacco were the same:1)compared with roasted tobacco mono-crop,tobacco-maize relay intercropping was beneficial to promote the growth of roots（lower ground）,reducing the stem and leaf weight（above ground）and nitrogen nutrient content of the tobacco plant,and increase the nutrient content of phosphorus and potassium in the tobacco plant.2)Compared with roasted tobacco monocropping,tobacco-maize relay intercropping was beneficial to increase SOD,POD,NR,and GS activities and decrease CAT activity and MDA content of tobacco plants.It is shown that roasted tobacco and maize crop is conducive to improving SOD and POD activities,further improving antioxidant enzyme activities,and then alleviating oxidative stress in tobacco by reducing CAT activity and MDA content.2.The effects of different roasted tobacco varieties with maize overcropping on the soil microenvironment of tobacco plants were consistent:1)Compared with roasted tobacco monocropping,roasted tobacco-maize relay intercropping was beneficial to improve soil p H,TP,AP,AK,AN,and NO₃^--N contents and reduce TN,TK,and NH₄⁺-N contents.This indicates that roasted tobacco and maize crop is conducive to improving the soil microenvironment,enhancing soil nutrient supply capacity,and promoting nutrient uptake by tobacco plants.2)Compared with roasted tobacco monocropping,tobacco-maize relay intercropping was conducive to promoting the increase of soil urease,sucrase,and phosphatase activities and decrease of peroxidase activity,and improve the soil properties of roasted tobacco root system.3)Compared with roasted tobacco monocropping,tobacco-maize relay intercropping was conducive to improving the soil microbial community structure of tobacco inter-root soil,the species richness（Chao1 index）of the bacterial community increased,showed an increase in the abundance of microorganisms such as Acidobacteria and Nitrospirae,and a decrease in the abundance of harmful microorganisms such as Chloroflexi;the species abundance（Chao1 index）and diversity（Shannon index）of fungal community decreased,showing the relative abundance of Mortierellomycota.Redundancy analysis（RDA）showed that soil TP,TN,AP,NO₃^--N,NH₄⁺-N,and SOC contents significantly affected soil microbial community structure.3.The effects of exogenous MeJA on the physiology of roasted tobacco in different roasted tobacco varieties crop with maize were the same:1)Compared with no MeJA spraying,exogenous MeJA spraying was beneficial to increase SOD,POD,NR,and GS activities and decrease CAT activity and MDA content in the leaves of tobacco plants.It was shown that exogenous MeJA was beneficial to improve the activity of SOD and POD,further improve the activity of antioxidant enzymes,and then alleviate the oxidative stress of tobacco by reducing CAT activity and MDA content,and promote the normal maturation of roasted tobacco.（2）Compared with no MeJA spraying,the exogenous MeJA spraying was beneficial to increase the ACC,ETH,and IAA contents in the leaves of tobacco plants and the GA3,JA,and SA contents in the roots of roasted tobacco.It showed that exogenous MeJA has a promoting effect on plant growth hormone and is beneficial to promote normal maturation of roasted tobacco.Further study by sand culture method showed that under different treatments,the contents of JA,SA,GA3,and ETH in the leaves of tobacco plants increased and the contents of ABA decreased,while ACC and IAA did not change significantly with the changing time of exogenous MeJA spraying.It is shown that exogenous MeJA has a promotional effect on plant growth hormone and is beneficial to promote tobacco maturation.4.The effects of exogenous MeJA on the soil microenvironment of different roasted tobacco varieties showed the same performance as follows:1)Compared with no MeJA spraying,the spraying of exogenous MeJA was beneficial to improve the soil p H,TP,AP,AK,NO₃^--N,SOC and SOM contents around the roots of roasted tobacco.It showed that exogenous MeJA was beneficial to improve the uptake and utilization of soil nutrients in the inter-root area of roasted tobacco.2)Compared with no MeJA spraying,exogenous MeJA spraying was beneficial to enhance soil urease,sucrase,catalase,acid,and neutral phosphatase activities around the roots of roasted tobacco.It showed that exogenous MeJA was beneficial to enhance the activity of inter-root soil-related enzymes in roasted tobacco,improve the uptake and utilization of inter-root soil nutrients by the tobacco plant,and promote the normal maturation of the tobacco plant.3)Compared with no MeJA spraying,inter-root soil bacterial richness,and diversity were significantly lower and inter-root fungal richness was significantly lower with exogenous MeJA spraying,but soil fungal diversity increased with K326,and microbial community composition showed that the relative abundance of Actinobacteria、Chloroflexi、Ascomycota、Basidiomycota、Mortierellomycota in inter-root soil of roasted tobacco decreased with MeJA spraying.Redundancy analysis（RDA）showed that soil TP,TN,AP,NO₃^--N,NH₄⁺-N,and SOC contents significantly affected soil microbial community structure.5.The effects of exogenous vinyl chloride on the soil microenvironment of different roasted tobacco varieties showed the same performance as follows:1)Compared with CK,soil TP,TK,AP,AK,NO₃^--N,NH₄⁺-N,SOM,SOC contents,and soil urease,catalase,sucrase,acid phosphatase,and neutral phosphatase activities were best with 0.2 m M vinyl chloride.2)Compared with CK,theα-diversity of soil bacteria and fungi（Shannon and Chao1 indices）was reduced by 0.1-0.2 m M concentration levels of ethylene glycol.RDA analysis showed that the soil microbial community structure of exogenous vinblastine was significantly and positively correlated with soil p H,TN,NO₃^--N,NH₄⁺-N SOM,and SOC.In conclusion,both roasted tobacco-maize relay intercropping and exogenous MeJA are beneficial to improve the antioxidant characteristics and metabolism of nitrogenous compounds in roasted tobacco,enhance the supply of soil nutrients around the root system,improve the soil microenvironment,and promote the normal maturation of the tobacco plant.At the same time,exogenous ethylene glycol was also beneficial to improve soil nutrient supply and enzyme activity in monoculture,improve inter-root microbial community diversity,and promote normal maturation of roasted tobacco,which can be applied in production.