Plant functional groups and phylogenetic regularity control plant community bioelement composition through calcium and magnesium

Abstract

The identification of drivers of bioelement concentrations in plant communities is crucial for our understanding of ecosystem functioning. In this respect, soil nutrients, plant biodiversity and functional groups are reported to affect the plant community bioelement composition. However, given the predominant focus on species richness and single elements (or stoichiometric ratios) so far, only little is known about the patterns of the whole suite of bioelements at the community level and whether these patterns can be predicted by evolutionary relationships between co-occurring species (phylogenetic diversity). To explore this knowledge gap, we used a comprehensive dataset of soil nutrients, plant community composition, phylogeny and aboveground tissue bioelement data from experimental sites established in central European semi-natural grasslands. Plant community bioelement composition was strongly and exponentially related to community calcium and magnesium (bioelements reflecting deep phylogenetic differences). Plant community bioelement composition and stoichiometry were best indicated by functional group composition (graminoids and forbs) and phylogenetic regularity, whereas phylogenetic richness, phylogenetic divergence and species richness were poor predictors. Bioelement-rich communities were poor in graminoids and rich in forbs, and tended to have evenly distributed phylogenetic distances (high regularity). No confounding effect of soil nutrients was observed. The links between functional group composition, phylogenetic regularity and plant community bioelement composition suggest that functional groups and phylogenetic diversity are mechanistically connected to ecosystem functions, such as primary production, decomposition, biogeochemical cycling or plant-herbivore interactions, through bioelements.

Plant chemical traits define functional and phylogenetic axes of plant biodiversity

“…A growing body of evidence suggests the ecological importance of interspecific differences in plant chemical traits, including both elemental concentration and secondary metabolites (Aerts & Chapin III, 2000; Bitomský et al, 2023; Fernández‐Martínez et al, 2021; Kaspari & Powers, 2016; Mládková et al, 2018; Peñuelas et al, 2019; Reich et al, 2005; Walker et al, 2022; White et al, 2012). The full elemental composition of a plant species has been called its elementome or ionome and is thought to be related to competitive abilities for different nutrients and to function as a biogeochemical niche (Peñuelas et al, 2019; Salt et al, 2008).…”

“…While our small number of species limits any broad evolutionary arguments, we demonstrate that both functional and phylogenetic differences underpinning ecosystem functioning can be described using tissue % Ca, N, K and B (Fernández‐Martínez, 2022). These findings lead us to wonder the extent to which plant species in tropical, temperate and boreal forests, deserts and other grasslands might be similarly differentiated (Bitomský et al, 2023; Fernández‐Martínez et al, 2021; Kaspari et al, 2021; Mládková et al, 2018; Neugebauer et al, 2020; Sardans et al, 2015, 2021; White et al, 2012). Might plant tissue ratios beyond solely N and P, but including K, Ca and/or B and Si be as insightful in terrestrial ecosystems as have been Redfield (1934) C:N:P ratios in aquatic ecosystems?…”

“…It seems plausible that chemical traits might offer insights into both plant competitive coexistence and plant evolutionary history (Broadley et al, 2003; Fernández‐Martínez et al, 2021; Neugebauer et al, 2018; Peñuelas et al, 2019; Walker et al, 2022; White et al, 2012). For example, differing requirements for elements such as N, P, K and Ca may allow competing plant species to coexist (Tilman, 1982), and may cause tissue levels of certain elements such as Ca to be phylogenetically conserved within plant families (Bitomský et al, 2023; Broadley et al, 2003; Mládková et al, 2018; Neugebauer et al, 2018; Sardans et al, 2021; White et al, 2012). From an ecosystem perspective, because of plant–soil feedback effects, interspecific differences in plant elemental chemistry could alter the quantities and the stoichiometric ratios of limiting elements in an ecosystem (Ehrenfeld et al, 2005; Furey & Tilman, 2021; Hobbie, 2015; Jobbágy & Jackson, 2001; Reich et al, 2005; Sterner & Elser, 2002; Waring et al, 2015; Wedin & Tilman, 1990; Zinke, 1962).…”

“…For example, boron (B) may be a limiting micronutrient for the tropical rainforest of Barro Colorado Island (Steidinger, 2015; Turner et al, 2017), and is one of the more limiting micronutrients in many agricultural soils (Shorrocks, 1997). Tissue % Ca has been shown to differentiate some plant families, with % Ca being low in grasses ( Poaceae ) relative to other angiosperm families (Bitomský et al, 2023; Broadley et al, 2003; Mládková et al, 2018; Neugebauer et al, 2018). Furthermore tree species within Acer have higher % Ca than those within Pinus (Reich et al, 2005).…”

Multiple dimensions of phylogenetic diversity are needed to explain the complex aboveground–belowground diversity relationships

“…For beta diversity at the richness dimension, such a correlation suggests that if both plant and microbial communities are more dissimilar then they are both exhibiting substantial compositional turnover such that different sites have many new phylogenetic branches. A positive relationship for the divergence dimension suggests that phylogenetically distantly related plants promote the co‐occurrence of phylogenetically distantly related microbes, which would be the signal of coevolution between plants and microbes (Bitomský et al 2022, Kohli et al 2022). For the beta diversity level, such correlation indicates that if plant and microbial communities are both more phylogenetically dissimilar then turnover between sites is occurring deeper in the phylogeny, likely reflecting an underlying selection gradient.…”