Variation in Soil Fungal Community Structure During Successive Rotations of Casuarina Equisetifolia Plantations As Determined by High-Throughput Sequencing Analysis

Regeneration failure and productivity decline, which is collectively known as consecutive monoculture problem (CMP), were observed during long-term monoculture Casuarina equisetifolia plantations. In this study, the high-throughput sequencing method was applied to determine whether the rhizospheric microbial community composition would be significantly degenerated by consecutive monoculture in C. equisetifolia plantations. The results showed that the soil fungal community structure exhibited obvious differences among the first rotation plantation (FCP), the second rotation plantation (SCP), and the third rotation plantation (TCP). Both the Shannon and Simpson diversity indices of the soil fungal community in the FCP were significantly higher than in the SCP ( P < 0.05). Additionally, the relative abundance of Fusarium, Thelephora, Hortaea and Penicillium were significantly higher in the SCP and TCP soils than in the FCP soils, suggesting that certain fungi gradually became predominant in the continuous monoculture plantation soils. Conversely, the relative abundance of Tolypocladium and Trichoderma were significantly lower in the SCP and TCP soils than in the FCP soils, suggesting that some microbes gradually decreased in the continuous monoculture plantation soils. Overall, the results demonstrated that the long-term pure plantation pattern exacerbated the microecological imbalance in rhizospheric soils of C. equisetifolia and markedly decreased soil microbial community diversity.