Ground-Penetrating Radar as phenotyping tool for characterizing intraspecific variability in root traits of a widespread conifer

Erica Lombardi,Jordi Voltas,Ulises Rodríguez-Robles,Víctor Resco De Dios,Juan Pedro Ferrio

doi:10.1007/s11104-021-05135-0

Abstract

Background and AimDrought is the main abiotic stress affecting Mediterranean forests. Root systems are responsible for water uptake, but intraspecific variability in tree root morphology is poorly understood mainly owing to sampling difficulties. The aim of this study was to gain knowledge on the adaptive relevance of rooting traits for a widespread pine using a non-invasive, high-throughput phenotyping technique.MethodsGround-Penetrating Radar (GPR) was used to characterize variability in coarse root features (depth, diameter and frequency) among populations of the Mediterranean conifer Pinus halepensis evaluated in a common garden. GPR records were examined in relation to aboveground growth and climate variables at origin of populations.ResultsVariability was detected for root traits among 56 range-wide populations categorized into 16 ecotypes. Root diameter decreased eastward within the Mediterranean basin. In turn, root frequency, but not depth and diameter, decreased following a northward gradient. Root traits also varied with climatic variables at origin such as the ratio of summer to annual precipitation, summer temperature or solar radiation. Particularly, root frequency increased with aridity, whereas root depth and diameter were maximum for ecotypes occupying the thermal midpoint of the species distribution range.ConclusionGPR is a high-throughput phenotyping tool that allows detection of intraspecific variation in root traits of P. halepensis and its dependencies on eco-geographic characteristics at origin, thereby informing on the adaptive relevance of root systems for the species. It is also potentially suited for inferring population divergence in resource allocation above- and belowground in forest genetic trials.

Highlights

Climate models forecast an increase in temperature along with an intensification of extreme weather events that will likely lead to more prolonged and intense drought periods around the globe (IPCC 2007, 2014)
A number of functional traits related to hydraulic conductivity such as root vessel diameter are determined by root xylem anatomy, which in turn is influenced by root diameter and rooting depth (Kirfel et al 2017; Wang et al 2015)
Seeds from 56 populations of P. halepensis originating from mainland Spain, Balearic Islands, France, Greece, Italy and Tunisia were used in this study

Summary

Introduction

Climate models forecast an increase in temperature along with an intensification of extreme weather events that will likely lead to more prolonged and intense drought periods around the globe (IPCC 2007, 2014). This future climate may have serious impacts on ecosystem dynamics in the Mediterranean basin (Resco de Dios et al 2007; Sardans and Peñuelas 2013). Species-specific and intraspecific differences in rooting patterns are still poorly characterized, This is mainly due to the inherent complexity of underground sampling (Alani and Lantini 2020) and the fact that traditional approaches for root monitoring, such as the Auger and the Monolith methods, are destructive and non-repeatable (Krainyukoy and Lyaksa 2016). Methods Ground-Penetrating Radar (GPR) was used to characterize variability in coarse root features (depth, diameter and frequency) among populations of the Mediterranean conifer Pinus halepensis

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