Intra‐ and inter‐specific variation in root mechanical traits for twelve herbaceous plants and their link with the root economics space

Abstract

Plant root traits are diverse and variable, and the way in which they interact has consequences for fundamental functions such as anchorage, or services such as soil fixation. Here, we characterize mechanical traits related to anchorage (tensile strength, strain, stiffness and toughness) at both intra‐ and inter‐specific levels and examine how they covary with other traits related to the root economics space. We grew twelve herbaceous species from contrasting taxonomical families in a common garden experiment. For each species, we excavated root systems and measured mechanical, morphological and chemical traits at two locations (proximal versus distal) for two root types (absorptive versus transport roots). At the intraspecific level, transport roots tended to be stronger and tougher than absorptive roots and could extend further before failure, but were as stiff as absorptiveroots. Where the root was sampled (proximalversus distal) had a limited effect on any root mechanical trait. The five monocots (Poaceae) had stronger and tougher root material than the seven dicots (Fabaceae, Plantaginaceae and Rosaceae), but there were no differences in stiffness. At the interspecific level, mechanical traits covaried positively and were strongly and positively correlated with specific root length (a trait related to the ‘do‐it‐yourself' soil exploration strategy), and negatively with root diameter (a trait related to the ‘outsourcing' soil exploration strategy) and root tissue density (a trait related to root lifespan). We demonstrate the important role of species' taxonomical subgroup (monocot versus dicot) and root type in governing mechanical trait variation at both intra‐ and inter‐specific levels. Our results can be regarded as the first evidence of a link between root mechanical robustness and the root economics space, through a strong association with the ‘do‐it‐yourself' soil exploration strategy.

Special Issue: Root traits and functioning: from individual plants to ecosystems

“…Whereas the work of Mao et al (2023), Stiblíková et al (2023) and Yang et al (2023) in this issue expanded the RES with fine root traits, others delved further, beyond the absorptive roots traditionally emphasized in fine-root studies. Klimešová and Herben (2023) study non-acquisitive belowground plant organs, like rhizomes or bud-bearing roots, of close to 1500 herbaceous species with different lifespans and clonality.…”

“…Reference in this Special Issue Temperate Alonso-Crespo et al 2023, Klimešová and Herben 2023, Mafa-Attoye et al 2023, Mao et al 2023, Schuster et al 2023, Slette et al 2023, Yang et al 2023(Sub)Tropical Dallstream et al 2023, Dai et al 2023,Gagliardi et al 2023, Guo et al 2023, Leroy et al 2023, Kotowska et al 2023 a large variety of fine-root systems coexist in hyper-diverse tropical plant communities. Besides adding information from underexplored biomes, this Special Issue further highlights the importance of incorporating additional traits covering all belowground trait categories (McCormack et al 2017) -albeit to different extents -in the context of a RES (Table 1).…”

“…In contrast, among ten shrub species, root foraging precision was associated with the collaboration axis, as those species with thick roots and low SRL had lower foraging precision and this may be explained by the greater mycorrhizal dependency of thick‐rooted species circumventing their need to produce highly exploitative, branched‐out roots (Yang et al 2023). In addition to root architectural traits, Mao and co‐workers (2023) examine root mechanical traits among 12 herbaceous species in relation to the RES. Those species that displayed the do‐it‐yourself strategy also had more mechanically robust roots (e.g.…”

“…Emerging evidence further suggests that not only mycorrhizal but also soil–borne pathogenic interactions shape the RES (Xia et al 2021). The work of Dai et al (2023) shows that (arbuscular mycorrhizal) tree species adopting the do‐it‐yourself strategy had higher root pathogen richness than species exhibiting the outsourcing strategy, potentially because high‐SRL roots have greater investments in root mechanics (Mao et al 2023) and thus lower investments in root chemical defense against infections by soilborne pathogens (Xia et al 2021). Together, these studies focusing on interspecific variation in a broad array of belowground traits and functions highlight the multidimensionality of the belowground, and bring forward relevant candidate (biotic) traits that would play a prominent role in expanding the current RES.…”

“…Several studies here further demonstrate the various traits involved in belowground resource uptake strategies, which are thus relevant in the context of a RES and of species' responses to environmental change. These include, but are not restricted to, root foraging precision (Stiblíková et al 2023, Yang et al 2023), productivity (Slette et al 2023, Yang et al 2023), mechanical traits (Mao et al 2023), exudation profiles (Dallstream et al 2023) and enzymatic capacities (Wang et al 2023), root biomass fractions and vertical distributions (Gagliardi et al 2023, Wang et al 2023, Yang et al 2023), mycorrhizal fungal traits (Weemstra et al 2023) or interactions with plant pathogens (Dai et al 2023). If e.g.…”