Climate, soil and plant functional types as drivers of global fine‐root trait variation

Abstract

International audience* Ecosystem functioning relies heavily on below-ground processes, which are largely regulated by plant fine-roots and their functional traits. However, our knowledge of fine-root trait distribution relies to date on local- and regional-scale studies with limited numbers of species, growth forms and environmental variation. * We compiled a world-wide fine-root trait dataset, featuring 1115 species from contrasting climatic areas, phylogeny and growth forms to test a series of hypotheses pertaining to the influence of plant functional types, soil and climate variables, and the degree of manipulation of plant growing conditions on species fine-root trait variation. Most particularly, we tested the competing hypotheses that fine-root traits typical of faster return on investment would be most strongly associated with conditions of limiting versus favourable soil resource availability. We accounted for both data source and species phylogenetic relatedness. * We demonstrate that: (i) Climate conditions promoting soil fertility relate negatively to fine-root traits favouring fast soil resource acquisition, with a particularly strong positive effect of temperature on fine-root diameter and negative effect on specific root length (SRL), and a negative effect of rainfall on root nitrogen concentration; (ii) Soil bulk density strongly influences species fine-root morphology, by favouring thicker, denser fine-roots; (iii) Fine-roots from herbaceous species are on average finer and have higher SRL than those of woody species, and N2-fixing capacity positively relates to root nitrogen; and (iv) Plants growing in pots have higher SRL than those grown in the field. * Synthesis. This study reveals both the large variation in fine-root traits encountered globally and the relevance of several key plant functional types and soil and climate variables for explaining a substantial part of this variation. Climate, particularly temperature, and plant functional types were the two strongest predictors of fine-root trait variation. High trait variation occurred at local scales, suggesting that wide-ranging below-ground resource economics strategies are viable within most climatic areas and soil conditions

Microenvironment and functional‐trait context dependence predict alpine plant community dynamics

“…excavation of whole root systems). To circumvent these issues, there is a need for further developing below‐ground trait databases (Freschet et al., ; Iversen et al., ) and fine‐scale soil maps (Arrouays et al., ).…”

Plant economic strategies of grassland species control soil carbon dynamics through rhizodeposition

“…Plant economic traits related to C‐photosynthate production ( A canopy ) and supply to the soil through rhizodeposition ( R H ‐SOC new ) seems to be more important determinants of the RPE than fine‐root morphological and architectural traits shaping the volume of rhizospheric soil and spatial distribution of rhizodeposition. This result should however be taken with cautious as fine‐root trait values are known to sometimes differ between plants growing in pots or in the field (Freschet et al, ). Species with thick roots and low SRL are usually associated with high level of mycorrhizal colonization (Ma et al, ).…”

Global drivers of fine root trait variation: Commentary on Freschet et al. (2017)

“…Freschet et al . () have taken the first critical step toward understanding global drivers of fine root form and function by synthesizing an extraordinary amount of fine root data from studies that span all vegetated continents (Iversen et al . ).…”

“…Specifically, Freschet et al . () provide the first global assessment of the relationships between four key fine root traits – fine root nitrogen (N) concentration, mean diameter, tissue density and specific root length (SRL) – and climate, soil properties, growth form and growing conditions.…”

“…), I am hopeful that Freschet et al . 's () paper will inspire ecologists around the world to hoist their spades and join us in the challenging yet critically important work of studying plant roots.…”