Determinism of biogeographical patterns and network interactions of soil fungal diversity across France
The fungal kingdom is among the most diversified kingdoms on earth with estimations up to 12 million species. Yet, it remains poorly understood with only 150,000 fungal species currently described. Given the major ecological role of fungi in ecosystem functioning, these numbers stress the importance of investigating fungal diversity description across different ecosystem types. Here, we explored the spatial distribution of the soil fungal diversity on a broad geographical scale, using the French Soil Quality Monitoring Network that covers the whole French territory (2,171 soils sampled along a systematic grid). Fungal alpha-diversity was assessed directly from soil DNA using a metabarcoding approach by targeting the 18S rDNA gene. The total accumulated fungal diversity across France included 136,219 OTUs, i.e., about 1% of worldwide soil fungal diversity (based on a maximum diversity estimate of 12 million) for a territory representing only 0.3% of terrestrial surface on Earth. Based on this dataset, the first extensive map of fungal alpha-diversity was drawn and evidenced a heterogeneous and spatially structured distribution in large biogeographical patterns of 231 km radius for richness (Hill diversity of order 0) and smaller patterns of 36 km radius for dominant fungi (Hill diversity of order 2). As related to other environmental parameters, the spatial distribution of fungal diversity (Hill numbers based on different orders of diversity) was mainly influenced by local filters such as soil characteristics and land management, but also by global filters such as climate conditions with various relative influences. Interestingly, cropped soils exhibited the highest pool of fungal diversity relatively to forest and vineyard soils. In complement, soil fungal OTUs network interactions were calculated under the different land uses across France. They varied hugely and showed a loss of 75% of the complexity in crop systems and grasslands compared to forests, and up to 83% in vineyard systems. Overall, our study revealed that a nation-wide survey with a high spatial resolution approach is relevant to deeply investigate the spatial distribution and determinism of soil fungal diversity. Our findings provide novel insights for a better understanding of soil fungal ecology across the 18S rDNA gene and upgrade biodiversity conservation policies by supplying representative repositories dedicated to soil fungi.