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Root-centric β diversity reveals functional homogeneity while phylogenetic heterogeneity in a subtropical forest

Luo, Wenqi1; Wang, Youshi1; Cahill Jr., James F.2; Luan, Fucheng3; Zhong, YongLin1; Li, Yuanzhi1; Li, Buhang1; Chu, Chengjin1

Published Oct 10, 2023; Updated Nov 06, 2023 on Dryad. https://doi.org/10.5061/dryad.2ngf1vhvm

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Oct 10, 2023 version files 284.77 KB
Nov 06, 2023 version files 284.87 KB

Abstract

Root-centric studies have revealed fast taxonomic turnover across root neighborhoods, but how such turnover is accompanied by changes in species functions and phylogeny (i.e. β diversity), which can reflect the degree of community-wide biotic homogenization, remains largely unknown, hindering better inference of below-ground assembly rules, community structuring, and ecosystem processes. We collected 2480 root segments from 625 0–30 cm soil profiles in a subtropical forest in China. Root segments were identified into 143 species with DNA-barcoding with six root morphological and architectural traits measured per species. By using the mean pairwise (Dpw) and mean nearest neighbor distance (Dnn) to quantify species ecological differences, we tested the non-random functional and phylogenetic turnover of root neighborhoods that would lend more support to deterministic over stochastic community assembly processes, examined the distance-decay pattern of β diversity, and finally partitioned β diversity into geographical and environmental components to infer their potential drivers of environmental filtering, dispersal limitation, and biotic interactions. We found that functional turnover was often lower than expected given the taxonomic turnover, whereas phylogenetic turnover was often higher than expected. Both functional and phylogenetic Dpw (e.g. interfamily species) turnover exhibited a distance-decay pattern, likely reflecting limited dispersal or abiotic filtering that leads to the spatial aggregation of specific plant lineages. Conversely, phylogenetic Dnn (e.g. intrageneric species) exhibited an inverted distance-decay pattern, likely reflecting strong biotic interactions among spatially and phylogenetically close species leading to phylogenetic divergence. While the spatial distance was generally a better predictor of β diversity than environmental distance, the joint effect of environmental and spatial distance usually overrode their respective pure effects. These findings suggest that root neighborhood functional homogeneity may somewhat increase forest resilience after disturbance by exhibiting an insurance effect. Likewise, root neighborhood phylogenetic heterogeneity may enhance plant fitness by hindering the transmission of host-specific pathogens through root networks or by promoting interspecific niche complementarity not captured by species functions. Our study highlights the potential role of root-centric β diversity in mediating community structures and functions largely ignored in previous studies.