Fine root morphological traits and root dynamics of beech, oak, pine and Douglas fir along a climatic aridity gradient

Abstract Aims The rapid rise in mean and extreme temperatures and in atmospheric and edaphic drought with climate warming exposes trees and forests to increasing stress. While much research has addressed aboveground tree organs, less is known about the drought resistance and response of the fine root system, the site of water and nutrient uptake. We aimed to assess how reduced precipitation influences root system size, dynamics, morphology, and potential acclimatization to water scarcity. Methods We studied fine root biomass (FRB), productivity (FRP), lifespan, and morphological traits of European beech, sessile oak, Scots pine, and Douglas fir in mature stands on deep sandy soils along a pronounced precipitation gradient (820 – 580 mm yr −1 ) and modelled the response to mean annual precipitation across sites. Results FRB increased in beech toward drier sites, decreased slightly in oak, and remained unchanged in pine and Douglas fir. FRP increased in beech and Douglas fir with drier conditions, but remained stable in oak and pine. All species exhibited increased root tissue density under drought, but only conifers showed a consistent shift to more conservative traits, reflected in longer root lifespan under reduced precipitation. Conclusions Our study reveals diverse belowground drought responses among the species, including altered fine root dynamics and morphological adjustments, indicating multiple resilience strategies. Root trait modifications, although minor, were complex, species-specific, and influenced by phylogeny, underscoring the need for further field studies and refined models to better understand belowground drought responses.