Abstract: Straw return and appropriate planting density are beneficial for improving soil physicochemical properties and optimizing microbial community structure. This study investigated the effect of different straw-returning modes (H1: straw crushing deep plowing back to the field, H0: straw was not returned to the field) and different planting densities (D1: 67500plants∙ha⁻¹, D2: 82500plants∙ha⁻¹, D3: 97500plants∙ha⁻¹) on the diversity and community structure of rhizosphere fungi at maize maturity using Illumina MiSeq high-throughput sequencing technology. The study was established as a split-plot experiment and conducted on maize farmland of the Yinhuang Irrigation area in Ningxia for five consecutive years. Results showed that: (1) the interaction effect of straw return mode and planting density was highly significant for the Chao1 index, ACE index, and Shannon index of soil fungal communities (P<0.01), with the indexes being highest under the H1D2 treatment. (2) Soil fungal community in the inter-root area of maize in the farmland was mainly composed of fungi from 509 genera in 14 phyla, such as Ascomycota (63.50%-81.82%), Basidiomycota (4.83%−18.03%), and Mortierellomycota (3.18%−9.61%), etc. The structure of the fungal community differed among different density and straw return mode combinations, and the relative abundance of the dominant phyla and genera varied greatly. (3) The interaction of straw return mode and planting density significantly influenced the soil pH, organic matter, alkaline dissolved nitrogen, and quick-acting phosphorus content (P<0.01), with H1D2 treatment being the optimal treatment combination. Pearson's correlation analysis showed that there were significant or highly significant correlations among soil pH, organic matter, total nitrogen, total phosphorus, alkaline dissolved nitrogen, quick-acting phosphorus, quick-acting potassium content, and the α-diversity of the fungi. Soil pH was significantly and negatively correlated with the relative abundance of Cladosporium (P<0.05). Organic matter, total phosphorus, alkaline-dissolved nitrogen. And quick-acting potassium content were significantly and positively correlated with the relative abundance of Cladosporium (P<0.05). Organic matter content was significantly and negatively correlated with the relative abundance of Chaetomium (P<0.05). RDA analyzes showed that total nitrogen, organic matter, fast-acting potassium, and pH were the main environmental factors that drive the variation of soil fungal communities in maize rhizosphere at different densities under different straw return patterns. In this study, straw return combined with a planting density of 82500 plants·ha⁻¹ was optimum for increasing farmland soil fertility and improving inter-root soil fungal diversity.

Key words: Straw returning, Planting density, Soil physicochemical properties, Fungal diversity, Fungal community structure