To study the effects of cotton stalk biochar on the regulation of fungal diversity, the structure and function of alkaline rice rhizosphere soil under cadmium pollution was investigated. An outdoor pot experiment was conducted by adding cotton stalk biochar (0%, 1%, and 5%) to an alkaline paddy soil with a cadmium concentration of 0.1 and 8 mg·kg-1. Taking rice rhizosphere soil as the research object, Illumina HiSeq sequencing was used to analyze the effects of cotton stalk biochar and cadmium pollution on the diversity, structure, abundance, and function of fungi in an alkaline rhizosphere soil, and to explore the correlation between soil environmental factors and the fungal community under the control of cotton stalk biochar. The results showed that:① the application of cotton stalk biochar significantly increased the soil pH, available nutrients, and organic matter, and reduced the content of reducible cadmium in the soil (P<0.05). ② The distribution of rice rhizosphere soil fungi was mainly Ascomycota, Aphelidiomycota, and Chytridiomycota, which accounted for 57% of all mycophytes. The genus was mainly Mortierella, Alternaria, and Fusarium. There was a significant difference in the α-diversity of the fungal community among the treatments (P<0.05). In the absence of cotton stalk biochar (C0), the increase in the cadmium concentration reduced the relative abundance and fungal diversity index (Shannon index) of Chytridiomycota, Mortierella, and Alternaria in the soil. Under different concentrations of cadmium (Cd0, Cd1, and Cd8), increasing cotton stalk biochar reduced the fungal community richness index (Chao1 index) and Shannon index. Cadmium pollution resulted in an increase in the relative abundance of Chytridiomycota in the soil, but decreased the abundance of Alternaria. The application of cotton stalk biochar could significantly increase the relative abundance of Chytridiomycota (P<0.05). Cadmium pollution reduced the abundance of Mortierella and Alternaria, but the application of cotton stalk biochar could increase the relative abundance of Alternaria. Increasing cotton stalk biochar means that soil will have more endophytes, plant pathogens, and saprophytes; while increasing cadmium pollution will reduce endophytes, plant pathogens, and saprophytes in the soil. ③ The main environmental factors affecting the diversity and structure of fungal communities are the available potassium, organic matter, and pH of the soil. The reducible cadmium content, which comprises the largest proportion of cadmium in rice soil, was significantly positively correlated to Rotifera, Aphelidiomycota, and Ascomycota (P<0.05), but negatively correlated to other mycophytes (P<0.05). The results indicate that cotton stalk biochar plays a certain role in the microecological regulation of alkaline cadmium-contaminated soil.
Keywords: cadmium; cotton stalk biochar; diversity; fungus; rhizosphere soil.