Response of soil fungal communities to continuous cropping of flue-cured tobacco

Abstract

Fungal communities are considered to be critically important for crop health and soil fertility. However, our knowledge of the response of fungal community structure to the continuous cropping of flue-cured tobacco is limited, and the interaction of soil fungal communities under different cropping systems remains unclear. In this study, we comparatively investigated the fungal abundance, diversity, and community composition in the soils in which continuous cropping of flue-cured tobacco for 3 years (3ys), 5 years (5ys), and cropping for 1 year (CK) using quantitative polymerase chain reaction and high-throughput sequencing technology. The results revealed that continuous cropping of flue-cured tobacco changed the abundance of soil fungi, and caused a significant variation in fungal diversity. In particular, continuous cropping increased the relative abundance of Mortierellales, which can dissolve mineral phosphorus in soil. Unfortunately, continuous cropping also increased the risk of potential pathogens. Moreover, long-term continuous cropping had more complex and stabilize network. This study also indicated that available potassium and available phosphorous were the primary soil factors shifting the fungal community structure. These results suggested that several soil variables may affect fungal community structure. The continuous cropping of flue-cured tobacco significantly increased the abundance and diversity of soil fungal communities.

Figure 1

Fungal abundance of fungal ITS gene (a), and the regression model of the relationship between the fungal abundance and (b) Shannon’ diversity index (H’ value), (c) Simpson’s diversity index. Different letters indicated significant differences among soil samples as calculated by One-way ANOVA and t test, (P < 0.01). 3ys: continuous cropping of flue-cured tobacco for 3 years. 5ys: continuous cropping of flue-cured tobacco for 5 years. CK: flue-cured tobacco cropping for 1 year.

Figure 2

The composition of the soil fungal communities at the phylum (a), and order (b) level in the three treatments. 3ys: continuous cropping of flue-cured tobacco for 3 years. 5ys: continuous cropping of flue-cured tobacco for 5 years. CK: flue-cured tobacco cropping for 1 year.

Figure 3

Fungal community structure indicated by non-metric multi-dimensional scaling (NMDS) plots of weighted (a), and unweighted (b) pairwise UniFrac distances. Principal coordinates analysis (PCoA) plot depicted the Bray–Curtis distance (c) of fungal communities. 3ys: continuous cropping of flue-cured tobacco for 3 years. 5ys: continuous cropping of flue-cured tobacco for 5 years. CK: flue-cured tobacco cropping for 1 year.

Figure 4

Redundancy analysis (RDA) demonstrating the relationships between soil properties and fungal community structures. The red font represents the fungal phyla with top 5 abundance; the blue arrows represent different soil properties. SOC: soil organic carbon, TN: total nitrogen, Ava-P: available phosphorus, Ava-K: available potassium. 3ys: continuous cropping of flue-cured tobacco for 3 years. 5ys: continuous cropping of flue-cured tobacco for 5 years. CK: flue-cured tobacco cropping for 1 year.

Figure 5

The co-occurrence network of soil fungi based correlation analysis. A connection stands for a strong (Spearman’s ρ > 0.6) and significant (P < 0.01) correlation. The nodes represent unique OTUs. The size of each node is proportional to degree. The nodes colored by taxonomy. 3ys: continuous cropping of flue-cured tobacco for 3 years. 5ys: continuous cropping of flue-cured tobacco for 5 years. CK: flue-cured tobacco cropping for 1 year.