Limiting similarity shapes the functional and phylogenetic structure of root neighborhoods in a subtropical forest

Abstract

Environmental filtering and limiting similarity mechanisms can simultaneously structure community assemblages. However, how they shape the functional and phylogenetic structure of root neighborhoods remains unclear, hindering the understanding of belowground community assembly processes and diversity maintenance. In a 50-ha plot in a subtropical forest, China, we randomly sampled > 2700 root clusters from 625 soil samples. Focusing on 10 root functional traits measured on 76 woody species, we examined the functional and phylogenetic structure of root neighborhoods and linked their distributions with environmental cues. Functional overdispersion was pervasive among individual root traits (50% of the traits) and accentuated when different traits were combined. Functional clustering (20% of the traits) seemed to be associated with a soil nutrient gradient with thick roots dominating fertile areas whereas thin roots dominated infertile soils. Nevertheless, such traits also were sorted along other environmental cues, showing multidimensional adaptive trait syndromes. Species relatedness also was an important factor defining root neighborhoods, resulting in significant phylogenetic overdispersion. These results suggest that limiting similarity may drive niche differentiation of coexisting species to reduce competition, and that alternative root strategies could be crucial in promoting root neighborhood resource use and species coexistence.

Plant evolution overwhelms geographical origin in shaping rhizosphere fungi across latitudes

“…Plant origin had a much smaller effect on the composition of fungal communities, though two invasive plants developed distinct assemblages of fungi than other plants in the greenhouse experiment. In addition, we detected no differences in richness and alpha diversity of associated fungi between native and invasive plants on average, in agreement with other studies (Koyama et al, 2019; Luo et al, 2021). In particular, we found no differences in the numbers and relative abundances of general and family/species‐specific pathogens or mutualists associated with these native versus invasive plants in the field and the greenhouse experiment (in particular, part of these OTUs in both field survey and greenhouse experiment were from the same 59 genera), suggesting that native soil fungi might have developed new co‐evolutionary relationships with these invasive plants.…”

“…However, such a pattern was absent for some functional guilds or at some latitudes and even reversed at 30.5°N for the overall and saprotrophic fungi, suggesting that some unexplored factors might have masked or even reversed such phylogenetic patterns in plant–soil fungi associations. In the field, a plant's rhizosphere microbiome could be affected by neighbouring plants, their effects could vary among functional guilds (Broz et al, 2007), and the roots of a plant were more likely to adjoin the roots of distant‐ versus closely related plants in the field, as predicted by the limiting similarity hypothesis (Luo et al, 2021). This might explain the observed departures in plant‐soil associations in this study and a meta‐analysis (Mehrabi & Tuck, 2015) of the expected phylogenetic conservatism.…”

“…In addition, the observed differing latitudinal pattern in compositional similarity in root fungi between invasive plants and between native plants might lead to biogeographic variations in plant interactions mediated by the soil biota. Two lines of evidence indicate that species that share similar soil microbes are likely to impose greater negative effects on each other via plant–soil interactions (Fitzpatrick et al, 2018; Luo et al, 2021). Therefore, the observed higher dissimilarity in fungal composition between invasive plants was likely to lead to invasion meltdown, as reported (Luo et al, 2021), but only at middle latitudes.…”

“…Two lines of evidence indicate that species that share similar soil microbes are likely to impose greater negative effects on each other via plant–soil interactions (Fitzpatrick et al, 2018; Luo et al, 2021). Therefore, the observed higher dissimilarity in fungal composition between invasive plants was likely to lead to invasion meltdown, as reported (Luo et al, 2021), but only at middle latitudes. All these predictions are worth further clarification.…”

Resolving whole‐plant economics from leaf, stem and root traits of 1467 Amazonian tree species

“…Moreover, rather than being strongly constrained by abiotic conditions, root traits seem over‐dispersed along soil gradients. Instead, belowground acquisition strategies seem to be driven by limiting similarity processes (Luo et al 2022021).…”