Effects of crop rotation and straw mulching on the structure of rhizosphere soil fungal communities in continuously cropped potatoes

In this study, we investigated the effects of corn rotation combined with straw mulching on the rhizosphere soil of long-term-cultivated potatoes that had been planted for eight consecutive years. To this end, we assessed the effects of the following four treatments: no straw mulching (CK), corn straw mulching (T1), corn rotation combined with corn straw mulching (T2), and corn rotation (T3). High-throughput sequencing, soil physical and chemical analyses, and multivariate statistical processing methods were used to assess and compare the effects of the four treatments on the composition and structure, dominant groups, and diversity of the soil fungal community, and related physical and chemical indicators in the rhizosphere of potatoes. Compared with the CK treatment, the T1, T2, and T3 treatments reduced the richness of soil fungi in the rhizosphere of potatoes; however, they increased the diversity of these fungi. The highest values for the Shannon index were obtained in response to treatment T2. The PCoA and cluster analyses were conducted, and based on the composition of the soil fungal community, the soils subjected to the four treatments could be divided into two groups, namely, CK-T1 and T2-T3. The dominant phyla of soil fungi in the rhizosphere of potatoes were Ascomycota, Basidiomycota, Mortierellomycota, and Chytridiomycota, and compared with the CK treatment. We found that the different treatments had significantly different effect on fungal phyla, with the proportion of Ascomycota declining in response to treatments T1 and T3, and increasing slightly following treatment T2. In addition, the proportion of Mortierellomycota generally increased, and that of Chytridiomycota increased sharply in the T2 and T3 treatments, whereas the proportion of Basidiomycota increased in the T1 treatment and declined in the T2 and T3 treatments. Corn rotation alone was found to result in significant changes in the composition and structure of the soil fungal community in the rhizosphere of potatoes and promoted increases in the proportion of the beneficial phylum Mortierellomycota in the soil. Furthermore, correlation analysis of environmental factors indicated that soil available nitrogen and soil urease were the main environmental factors influencing the rhizosphere soil fungal community. The T2 and T3 treatments contributed to improving the soil microenvironment and reduced the proportion of the harmful genus Plectosphaerella by 48.1% and 45.0%, respectively. Our findings in this study revealed that corn rotation combined with straw mulching can contribute to significant increases in the contents of soil organic matter, alleviate the occurrence and spread of potato diseases, improve crop quality and yield, and effectively reduce the occurrence of soil-borne diseases.