Contrasting Latitudinal Patterns of Arbuscular Mycorrhizal Fungal Diversity in Sorghum Rhizosphere Versus Bulk Soils Across Climatic Zones

Arbuscular mycorrhizal (AM) fungi form symbionts with plant roots and contribute critically to the nutrient acquisition and health maintenance of crops. However, the diversity and maintenance mechanisms of AM fungi in large-scale agroecosystems remain poorly understood. We collected 534 samples from 55 sorghum fields spanning subtropical, warm temperate and temperate climatic zones. AM fungal diversity in both rhizosphere and bulk soils was examined using high-throughput sequencing. Results showed that AM fungal α-diversity in rhizosphere soils declined with increasing latitude, with the highest α-diversity being observed in the subtropical zone. Bulk soil-inhabiting AM fungal α-diversity followed an opposite trend, with higher richness detected in the temperate zone. AM fungal β-diversity, however, exhibited an inverse trend compared to α-diversity, increasing with latitude in the rhizosphere soils but decreasing with latitude in the bulk soils. Moreover, the difference in β-diversity between the two compartments decreased with increasing latitude, indicating that environmental filtering may be stronger at higher latitudes, thereby reducing the differentiation between rhizosphere and bulk soils. AM fungal communities were mainly influenced by deterministic processes irrespective of the compartment, and their large-scale community composition was jointly shaped by multiple factors, particularly mean annual precipitation, latitude and soil pH. These findings provide new insights into AM fungal diversity and community assembly patterns in large-scale agroecosystems.