Relationships among Soil Physicochemical Properties, Fungal Communities, and Flue-cured Tobacco Yield in Tobacco Continuous Cropping in Shandong Province

In order to clarify the effects of continuous cropping on the physicochemical properties of tobacco-growing soil, the yield of flue-cured tobacco and the characteristics of fungal community, and the relationship among them, the physicochemical properties of soil, the yield of flue-cured tobacco and fungal community were measured in Shandong Province with different continuous cropping years as the research object and non-continuous cropping soil as the control. With increasing continuous cropping years, the contents of organic matter, available nitrogen, available phosphorus and available potassium in tobacco continuous cropping soil decreased, the yield, average purchase price and total output value of flue-cured tobacco in continuous cropping plots also exhibited a decreasing trend. The response relationship between soil physicochemical properties and flue-cured tobacco yield revealed that pH, available nitrogen and available phosphorus were significantly correlated with flue-cured tobacco yield. The results of soil fungal community characteristics showed that continuous cropping led to the decrease of microbial diversity in tobacco-growing soil, and ACE index, Chao1 index, and Shannon index decreased significantly as continuous cropping years increased. PCoA analysis showed that continuous cropping changed the structure of fungal community in tobacco-growing soil. Continuous cropping of tobacco affected the relative abundance of dominant fungal taxa in tobacco-growing soil at the phylum level and genus level. The relative abundance of Ascomycota decreased, the relative abundance of Basidomycota and Mortierella increased, and the relative abundance of Tausonia, Mortierella, Fusarium and Gibberella increased. The results of soil fungal trophic composition showed that the overall proportion of pathotrophic type, saprophytic type and saprophytic-symbiotic type of continuous cropping soil increased. The co-occurrence network model revealed that tobacco continuous cropping simplifies the complexity of fungal community in tobacco-growing soil, and reduces the relationship between species and community stability. In the fifth year of tobacco continuous cropping, the positive correlation between fungal species in tobacco-growing soil accounts for a higher proportion. Spearman analysis showed that the abundance of dominant fungi in tobacco continuous cropping soil was related to pH, available nitrogen and available phosphorus. To sum up, the increase of tobacco continuous cropping years led to the decline of soil nutrients and the change of fungal community, which jointly drove the decline of flue-cured tobacco yield and total output value. Soil pH, available nitrogen and available phosphorus are the key environmental factors affecting flue-cured tobacco yield and enrichment of dominant bacteria.