| Mountain tobacco currently serves as the primary source of tobacco production in China.The development of mountain flue-cured tobacco holds a significant sway over the production of high-quality tobacco in the country.This experiment was conducted in Zunyi City,Guizhou Province in 2021 and 2022,utilizing Yunyan 87 as the test tobacco variety.Four treatments of biochar-based fertilizer application rates were set up: CK(conventional fertilization),T1(conventional fertilization with 10% nitrogen reduction + 0.6 t·hm-2 biocharbased fertilizer),T2(conventional fertilization with 10% nitrogen reduction + 0.9 t·hm-2biochar-based fertilizer),and T3(conventional fertilization with 10% nitrogen reduction + 1.2t·hm-2 biochar-based fertilizer).The effects of varying application rates of biochar-based fertilizers on tobacco soil’s physicochemical and biological characteristics,microbial community structure,and tobacco plant growth and development were studied.Based on the initial year of the experiment,two altitude gradients of 900 m(L)and 1200 m(H)were set up,with conventional fertilization(HCK,LCK)and 0.9 t·hm-2 biochar treatment(HT,LT)for a total of four treatments.This study explored the effects of biochar-based fertilizers on soil microecology and tobacco plant growth at different altitudes.High-throughput sequencing was utilized to analyze the changes in soil microecology after biochar-based fertilizer application at varying application rates and altitude gradients.Furthermore,extensive targeted metabolomics technology was used to study changes in tobacco leaf metabolites.This study not only provides technical support for high-quality tobacco production in the southwestern mountainous tobacco-growing areas of China but also offers a scientific basis for the rational application of biochar-based fertilizers in agricultural production.The main research results are as follows:(1)The application of biochar-based fertilizers significantly increased soil p H and reduced soil bulk density,with the treatment of 1.2 t·hm-2 biochar-based fertilizer showing the most significant improvement in soil organic matter and soil available nutrient content.Compared with the control,the application of biochar-based fertilizers significantly increased soil p H.After applying biochar-based fertilizers,soil bulk density decreased by 6.33%,12.41%,and 16.46%,respectively,reaching a significant level.After applying biochar-based fertilizers,the content of soil organic matter,alkaline hydrolysis nitrogen,available phosphorus,and available potassium all increased significantly compared with the control,with an increase of 19.05% to 27.64%,5.25% to 14.67%,4.99% to 15.16%,and 5.07% to14.83%,respectively.(2)The abundance of soil bacteria showed an increasing trend with the increase in the application rate of biochar-based fertilizer,followed by a decreasing trend.The application of biochar-based fertilizer reduced the diversity of soil fungi and significantly affected the structure of soil microbial communities.The relative abundance of Proteobacteria was lower in the 1.2 t·hm-2 biochar-based fertilizer treatment compared to the control.The changes in the relative abundance of Actinobacteriota and Chloroflexi were consistent among the four treatments and ranked as follows: 0.9 t·hm-2 > 1.2 t·hm-2 > 0.6 t·hm-2 > control.The relative abundance of Basidiomycota was increased by 149.85% and 64.25% in the 0.6 t·hm-2 and 0.9t·hm-2 biochar-based fertilizer treatments,respectively,compared to the control,while the relative abundance of Glomeromycota was decreased by 64.74% and 50.42%,respectively.(3)Moderate application of biochar-based fertilizers is beneficial to the growth and development of tobacco,promotes photosynthesis of tobacco,and has a certain coordinating effect on the chemical composition of tobacco leaves.It significantly increases the content of neutral aroma substances in tobacco leaves after roasting.The height of tobacco plants shows a trend of first increasing and then decreasing with the increase of biochar-based fertilizer application.The 0.9 t·hm-2 biochar-based fertilizer treatment shows the best growth performance of tobacco plants,reaching a maximum at 105 days,which is 16.07% higher than the control.Compared with the control treatment,the new plant diterpene content of roasted tobacco leaves is significantly increased after applying biochar-based fertilizer,among which the 0.9 t·hm-2 biochar-based fertilizer treatment has the highest content,increasing by 58.06%compared with the control.(4)After applying biochar-based fertilizer,there were significant differences in the metabolites of tobacco leaves,with a total of 103 metabolites being up-regulated or downregulated between the control and 0.9 t·hm-2 biochar-based fertilizer treatments.Among them,alkaloids,phenolic acids,and flavonoids were the metabolites that showed the most differences between the two treatments.(5)In high-altitude areas,the application of biochar-based fertilizer significantly increased the stem girth,maximum leaf length,and maximum leaf width of tobacco plants,by 26.87%,12.39%,and 20.45%,respectively.In low-altitude areas,the application of biochar-based fertilizer significantly increased the plant height of tobacco plants,while the stem girth,maximum leaf length,and leaf width all showed a significant decrease.(6)After applying biochar-based fertilizer,soil p H increased by 6.30% and 4.92% in highaltitude and low-altitude regions,respectively.Organic matter content increased by 10.23%and 9.84%,and available nitrogen content increased by 19.83% and 12.19% in the two regions.Available phosphorus content increased by 13.91% and 19.11%,and available potassium content increased by 10.70% and 12.58%,respectively.(7)After applying biochar-based fertilizer,the bacterial diversity and richness in lowaltitude soil were significantly increased,while the bacterial and fungal diversity and richness in high-altitude soil were significantly reduced.The bacterial diversity in high-altitude soil was significantly higher than that in low-altitude soil.The application of biochar-based fertilizer drove the construction of soil microbial community structure and changed the soil bacterial community structure at different altitudes. |
