Body size determines soil community assembly in a tropical forest

Abstract

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.

Latent Dirichlet Allocation reveals spatial and taxonomic structure in a DNA‐based census of soil biodiversity from a tropical forest

“…To test the practical relevance of LDA for the analysis of DNA‐based biodiversity censuses at the community scale, we applied it to a thorough soil metabarcoding survey at a tropical forest site (Zinger et al, ). This empirical data set was collected over relatively homogeneous environmental conditions and over a limited area (a 400 × 300‐m plot).…”

“…The fact that spatial patterns were similar between bacteria and protists, and also with fungi to a lesser extent, suggests similar constraints on the environmental filtering of unicellular organisms at the scale of the plot. In contrast, micro‐ and mesofauna communities were less structured, which may be explained by a stronger influence of neutral processes relative to environmental filtering on larger organisms (Zinger et al, ). The exposed rock assemblage stood out as being remarkably consistent across groups, including arthropods and nematodes.…”

“…We compare the performance of the method for a range of simulated OTU abundance and co‐occurrence structures. We then apply our approach to an empirical metabarcoding data set, which describes fine‐scale patterns of soil biodiversity across a pristine tropical forest plot in French Guiana (Zinger et al, ). Finally, we discuss and contrast our results in light of those obtained using more traditional multivariate methods.…”

Towards an integrative understanding of soil biodiversity

“…This may reflect the limited (active) dispersal capacity of soil organisms compared with organisms living aboveground or in aquatic systems (Anderson, 1975;Van der Putten et al, 2001;Wardle, 2002;Decaëns, 2010). With a limited capacity to disperse actively (larger soil organisms being an exception), passive dispersal is common in soil organisms (Nemergut et al, 2013;Schuppenhauer, Lehmitz, & Xylander, 2019;Zinger et al, 2019). For example, meso-fauna living in the S compartment, including collembolans and soil micro-arthropods are poor active dispersers but are often passively dispersed in the soil (Ettema & Wardle, 2002;Türke, Lange, & Eisenhauer, 2018;Schuppenhauer et al, 2019).…”

“…Although the dispersal ability of soil organisms will vary among different spatial compartments, it is important to note that species traits and soil structure will both impose challenges on the dispersal of soil organisms. The diversity of larger soil organisms may be related to active dispersal potential, whereas that of smaller organisms may be more affected by passive dispersal (Bahram et al, 2016;Zinger et al, 2019).…”