Ground-penetrating Radar as Phenotyping Tool for Characterizing Intraspecific Variability in Root Traits of Pinus Halepensis

Background and AimDrought is the main factor limiting Mediterranean forest ecosystem productivity. Root systems are responsible for water uptake but intraspecific variability in root morphology is poorly understood, mainly due to sampling complexity. The main aim of this study was to gain knowledge on the adaptive relevance of rooting traits for a widespread conifer using a non-invasive high-throughput technique.MethodsGround-Penetrating Radar (GPR) was used to characterize variability in coarse root features (frequency, depth, and diameter) among populations of the Mediterranean pine Pinus halepensis evaluated in a common garden. GPR records were analysed in relation to aboveground growth and also climate variables at origin of populations.ResultsGenotypic variability was detected for root traits among 56 range-wide populations categorized into 16 ecotypes. Root diameter of populations decreased eastward within the Mediterranean basin. Root frequency, but not depth and diameter, decreased following a northward gradient. Genotypic variation in root traits varied with climatic variables at origin such as summer to annual precipitation ratio, summer temperature and solar radiation. Particularly, root frequency increased with aridity, whereas root depth and diameter were maximum in ecotypes occupying the thermal midpoint of the species distribution range.Conclusion GPR is a high-throughput phenotyping tool that allows detection of intraspecific variation in root traits of Aleppo pine and its dependencies of 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.