We aimed to enhance understanding of the molecular diversity of arbuscular mycorrhizal fungi (AMF) by building a new global dataset targeting previously unstudied geographical areas. In total, we sampled 96 plant species from 25 sites that encompassed all continents except Antarctica. AMF in plant roots were detected by sequencing the nuclear SSU rRNA gene fragment using either cloning followed by Sanger sequencing or 454-sequencing. A total of 204 AMF phylogroups (virtual taxa, VT) were recorded, increasing the described number of Glomeromycota VT from 308 to 341 globally. Novel VT were detected from 21 sites; three novel but nevertheless widespread VT (Glomus spp. MO-G52, MO-G53, MO-G57) were recorded from six continents. The largest increases in regional VT number were recorded in previously little-studied Oceania and in the boreal and polar climatic zones - this study providing the first molecular data from the latter. Ordination revealed differences in AM fungal communities between different continents and climatic zones, suggesting that both biogeographic history and environmental conditions underlie the global variation of those communities. Our results show that a considerable proportion of Glomeromycota diversity has been recorded in many regions, though further large increases in richness can be expected in remaining unstudied areas.

Tropical forests shelter an unparalleled biological diversity. The relative influence of environmental selection (i.e., abiotic conditions, biotic interactions) and stochasticdistance-dependent neutral processes (i.e., demography, dispersal) in shaping communities has been extensively studied for various organisms, but has rarely been explored across a large range of body sizes, in particular in soil environments. We built a detailed census of the whole soil biota in a 12-ha tropical forest plot using soil DNA metabarcoding. We show that the distribution of 19 taxonomic groups (ranging from microbes to mesofauna) is primarily stochastic, suggesting that neutral processes are prominent drivers of the assembly of these communities at this scale. We also identify aluminium, topography and plant species identity as weak, yet significant drivers of soil richness and community composition of bacteria, protists and to a lesser extent fungi. Finally, we show that body size, which determines the scale at which an organism perceives its environment, predicted the community assembly across taxonomic groups, with soil mesofauna assemblages being more stochastic than microbial ones. These results suggest that the relative contribution of neutral processes and environmental selection to community assembly directly depends on body size. Body size is hence an important determinant of community assembly rules at the scale of the ecological community in tropical soils and should be accounted for in spatial models of tropical soil food webs. K E Y W O R D SDNA metabarcoding, eDNA, French Guiana, multitaxa, neutral assembly, niche determinism, propagule size, soil diversity | 529 ZINGER Et al.