Root Branching Is a Leading Root Trait of the Plant Economics Spectrum in Temperate Trees

Abstract

Global vegetation models use conceived relationships between functional traits to simulate ecosystem responses to environmental change. In this context, the concept of the leaf economics spectrum (LES) suggests coordinated leaf trait variation, and separates species which invest resources into short-lived leaves with a high expected energy return rate from species with longer-lived leaves and slower energy return. While it has been assumed that being fast (acquisitive) or slow (conservative) is a general feature for all organ systems, the translation of the LES into a root economics spectrum (RES) for tree species has been hitherto inconclusive. This may be partly due to the assumption that the bulk of tree fine roots have similar uptake functions as leaves, despite the heterogeneity of their environments and resources. In this study we investigated well-established functional leaf and stature traits as well as a high number of fine root traits (14 traits split by different root orders) of 13 dominant or subdominant temperate tree species of Central Europe, representing two phylogenetic groups (gymnosperms and angiosperms) and two mycorrhizal associations (arbuscular and ectomycorrhizal). We found reflected variation in leaf and lower-order root traits in some (surface areas and C:N) but not all (N content and longevity) traits central to the LES. Accordingly, the LES was not mirrored belowground. We identified significant phylogenetic signal in morphological lower-order root traits, i.e., in root tissue density, root diameter, and specific root length. By contrast, root architecture (root branching) was influenced by the mycorrhizal association type which developed independent from phylogeny of the host tree. In structural equation models we show that root branching significantly influences both belowground (direct influence on root C:N) and aboveground (indirect influences on specific leaf area and leaf longevity) traits which relate to resource investment and lifespan. We conclude that branching of lower order roots can be considered a leading root trait of the plant economics spectrum of temperate trees, since it relates to the mycorrhizal association type and belowground resource exploitation; while the dominance of the phylogenetic signal over environmental filtering makes morphological root traits less central for tree economics spectra across different environments.

The role of fine‐root mass, specific root length and life span in tree performance: A whole‐tree exploration

“…Currently, plant ecologists seek to identify the multiple dimensions of fine‐root trait variation related to plant performance (Laliberté, ; Liese, Alings, & Meier, ; Valverde‐Barrantes & Blackwood, ; Wang et al, ; Weemstra et al, ). This study demonstrates that fine‐root mass and length density—in combination with fine‐root life span—can represent an additional below‐ground dimension to capture species’ variation in performance.…”

The added value of including key microbial traits to determine nitrogen‐related ecosystem services in managed grasslands

“…Since this study aimed to highlight the relative contribution of microbial properties to the environmental processes, the measured root functional traits were assumed as good proxies of nutrient acquisition and different classes of root orders and diameter were not considered. Indeed, root biomass and SRL together reflect a plant's ability to prospect soil and take up nutrients (Craine, Wedin, Chapin, & Reich, ; Legay, Personeni, Slezack‐Deschaumes, Piutti, & Cliquet, ) and root N content is correlated with root branching, which is also a well‐established proxy of nutrient uptake potential (Liese, Alings, & Meier, ).…”

Fine‐root traits are linked to species dynamics in a successional plant community

“…Given that resource uptake by roots can be optimized in multiple ways (Weemstra et al 2016), far more information on root traits is needed to capture the full range of root foraging strategies and constrain their perceived relationship with species dynamics. For example, having more information on associations with mycorrhizal fungi, fine-root architecture, fine-root life span, and phenology should enable future studies to more fully define strategies of resource allocation and acquisition (Bouda and Saiers 2017, Liese et al 2017. Moreover, the majority of currently available data pertain to fine roots pooled as all roots <2 mm, which mixes distal, absorptive roots that generally lack secondary development with roots primarily involved in resource transport; this muddies the functional application of root trait information.…”