Patterns in intraspecific variation in root traits are species‐specific along an elevation gradient

Abstract

Patterns in intraspecific variation in root traits are species-specific along an elevation gradient Abstract 1. Intraspecific trait variation is an important driver of plant performance in different environments. Although roots acquire essential resources that vary with the environment, most studies have focused on intraspecific variation in leaf traits, and research on roots is often restricted to a few species. It remains largely unclear how and to what extent root traits vary with the environment and whether general intraspecific patterns exist across species. 2. We compared intraspecific variation in specific root length (SRL), root diameter, root tissue density (RTD) and root branching density of 11 species along a 1000 m elevation gradient in the French Alps. We tested 1) the extent of intra-versus interspecific root trait variation along the gradient, 2) whether intraspecific trait patterns with elevation were consistent among species and 3) whether environmental variables better explained intraspecific variation in root traits than elevation. Specifically, we hypothesised that within a species, root trait values would adjust to enhance resource acquisition (either through an increase in SRL or root diameter, and/or branching density) and/or conservation (increased RTD) at higher elevations. 3. Species identity explained most of the overall variation in root traits. Elevation explained only a minor proportion of intraspecific root trait variation, which varied more strongly within than between elevations. Also, trait relationships with elevation rarely agreed with our hypotheses, Accepted Article This article is protected by copyright. All rights reserved varied strongly across species, and were often differently related to environmental variation. Generally, climate, soil and vegetation properties better explained intraspecific root variation than elevation, but these relationships were highly species-dependent. 4. Along complex environmental gradients where multiple properties simultaneously change, roots of different species vary in different ways, leading to species-specific patterns in intraspecific root trait variation. The lack of support for our hypotheses may be caused by the multiple interactions between environmental properties, small-scale soil heterogeneity, species phylogeny, and changing plant-plant interactions. Our findings suggest that, to enhance our understanding of the effects of environmental change on plant performance, we need to better integrate the multiple dimensions of plant responses to change and measure a broader set of root traits and environmental variables.

An integrated framework of plant form and function: the belowground perspective

“…Here, we observed very similar trade‐offs between global species means and individual‐based datasets. Although we deem our results to be generally robust, there remains substantial uncertainty surrounding the amount and importance of intraspecific variation and plasticity in trait analyses (Sultan, 2000; Weemstra et al ., 2021). Additional work is needed to investigate the ranges of variation within and across species and, given the focus of the current study, it would be particularly interesting to know whether there is more variation in above‐ or belowground traits.…”

Patterns of genetic diversity vary among shoot and root functional traits in Norway spruce Picea abies along a latitudinal gradient

“…Here, seedlings from different populations of Norway spruce grew in controlled chamber environments that mimicked natural light and temperature cycles within a latitudinal gradient, revealing trait‐dependent patterns of among‐population variation that could signal adaptation to varied environmental factors. Based on the current results and related common‐garden and in situ studies on conifers (Ostonen et al 2011, 2017, Zadworny et al 2016, Weemstra et al 2021), traits that express root system size, the proportion of fine roots within root systems and biomass allocation to roots versus shoots may be more useful belowground complements to climate‐related shoot traits than branching intensity and specific root length. Together, the coexisting intraspecific phenomena of genetic diversity, multidimensionality of functional traits and phenotypic plasticity may echo robust survival strategies of long‐lived species in habitats that are characterised by consequential spatial and temporal heterogeneity and changing selective pressures (Aitken et al 2008, Laughlin 2014).…”

“…The finding of no latitudinal trend in branching intensity and specific root length within this geographic region is in agreement with the results of Ostonen et al (2017) who measured the same traits in fine roots of the same species at five sites between 60° and 68°N in Finland. More recently, Weemstra et al (2021) noted that variation in branching intensity and specific root length of fine roots in Norway spruce in situ was higher within elevations than across a 600‐m elevational range in the French Alps. However, Ostonen et al (2011) found that root tip length and fine root biomass were larger in higher‐latitude Norway spruce stands in Finland, and a common‐garden study with eastern European origins of Scots pine described a parallel positive correlation between latitude and the percentage of absorptive fine roots (Zadworny et al 2016).…”

“…Still, in studies on intraspecific adaptation, an appreciable imbalance persists in trait representation across the entire plant phenotypic spectrum that stems largely from laborious phenotyping required for fine root traits expected to regulate resource acquisition in heterogenous soils and overall plant performance, including architecture, morphology and physiology of different size‐based classes of fine roots and belowground associations with microbes (Freschet et al 2022021). Meanwhile, ecological research on the adaptive benefit of root variation has accentuated interspecific differences in fine roots of adult trees sampled in situ and their environmental determinants (Weemstra et al 2016, Laliberté 2017, Freschet et al 2022021), and in cases where attention has been drawn to significant intraspecific variation (Ostonen et al 2007, 2011, 2017, Defrenne et al 2019, Weemstra et al 2021), the genetic and plastic elements of trait variability are inseparable. Consequently, a common‐garden technique combined with comprehensive phenotyping is required to detect the heritable component in root functional trait variation and to determine whether comparable levels of among‐population differentiation have emerged along the entire plant phenotypic spectrum from shoot to root.…”

Shifts in soil and plant functional diversity along an altitudinal gradient in the French Alps

“…We present data collected in 2018, at six altitudes along an elevational gradient (1400–2400 m), at Massif de Belledonne, France (Table 1 , file 1, [ 5 ]). Bedrock was composed of Variscan metamorphic rocks and ophiolitic complexes.…”