Effects Of Tobacco Continuous Cropping On Agronomic Characters And Rhizosphere Microorganisms Of Different Crops

This experiment was conducted in the tobacco and post-tobacco small spring crop planting area in Ziwu Town,Chuxiong City,Yunnan Province.The study used tobacco and three different small spring crops,including barley,quinoa,and fava beans,as materials.By comparing the soil physical and chemical properties of continuous cropping and rotation,comparing the abundance,diversity,community composition,and gene abundance of soil microorganisms,the study aimed to clarify the impact of different ecological factors on the rhizosphere microbial community of tobacco fields.The agronomic traits of tobacco and three different small spring crops were investigated and compared to explore the relationship between them.The study provides theoretical support for ensuring the health of tobacco field soil and improving tobacco planting systems through the adoption of biotechnological measures.(1)From the perspective of soil physical properties,after planting,the bulk density of tobacco soil under continuous cropping treatment was 0.72% higher than that under rotation treatment,and the total porosity of tobacco soil under continuous cropping treatment was 5.04% lower than that under rotation treatment.Continuous cropping of tobacco caused adverse changes in the soil structure of the plow layer,affecting the exchange of water,nutrients,air,and heat in the soil.(2)In terms of soil nutrient status,during the growth period,continuous cropping of tobacco resulted in an average decrease of 5.56%,12.02%,6.75%,and 6.78%in soil hydrolyzed N content,available P content,available K content,and soil organic matter content,respectively,compared to rotation treatment.The soil p H value also decreased by an average of 4.27%.Continuous cropping of tobacco led to a decrease in soil available nutrients,resulting in poor growth and development of crops.For spring crops,there was little difference in the effect of continuous cropping and rotation of tobacco on the soil nutrient status of quinoa.However,post-tobacco barley and posttobacco fava beans had a certain effect on improving soil nutrient status under continuous cropping of tobacco.(3)In terms of agronomic traits of different crops,the continuous cropping obstacle significantly limited the growth and development of tobacco,with an average decrease of 10.51% in maximum leaf area.Continuous cropping of tobacco also had differential effects on three spring crops in the following rotation,with an average increase of 72.41% in the number of spikes per plant in barley under continuous cropping of tobacco treatment,an average decrease of 50.53% in spike length in quinoa under continuous cropping of tobacco treatment,and an average decrease of 30.30% in the number of pods per plant in fava beans under continuous cropping of tobacco treatment.The continuous cropping obstacle of tobacco can worsen the growth of quinoa and fava beans in the following rotation,but can increase the number of spikes per plant in barley.(4)In terms of soil microorganisms,the use of metagenomic molecular sequencing methods to study soil microbial ecology showed that there were certain differences in soil microbial diversity and abundance between tobacco and other crops.Continuous cropping of tobacco reduced the abundance and diversity of soil bacterial communities,but the dominant bacterial groups,including beneficial bacteria,did not show significant changes.Under continuous cropping of tobacco treatment,there were differences in horizontal microbial diversity among different spring crops,and continuous cropping of tobacco reduced the relative abundance of beneficial bacterial genera such as Porphyrobacter in quinoa soil,Roseimicrobium in barley soil,and Lacibacter in fava bean soil.(5)Enrichment analysis of functional differential genes in soil using metagenomics showed that the main functions of tobacco soil microbial genes were related to plant signal transduction,photosynthesis,and metabolism of sugars and sulfur.The main functions of tobacco-quinoa soil microbial genes were related to nitrogen and energy utilization,as well as DNA repair.The main functions of tobacco-barley soil microbial genes may affect the growth and metabolism of barley by regulating the metabolic processes of plant organelles and the absorption and transport of elements.The main functions of tobacco-fava bean soil microbial genes were related to carbohydrate metabolism and energy metabolism,indicating that soil microorganisms also play an important role in carbon cycling and energy flow in the soil after fava bean planting.