Impact of local soil and subsoil conditions on inter-individual variations in tree responses to drought: insights from Electrical Resistivity Tomography

Abstract

Inter-individual variability of tree drought responses within a stand has received little attention. Here we explore whether the spatial variations in soil/subsoil properties assessed through electrical resistivity tomography (ERT) could explain variations in drought response traits among trees.  We used ERT to compute the percent variation in resistivity (PVR) between dry and wet conditions as an indicator of spatial variability in total available water content. PVR was computed in two different depth ranges (0-2 and 2-5 m) for eleven Quercus ilex stools in a Mediterranean forest stand. PVR values were compared to biological traits, including tree water status (predawn water potential (Ψ)), leaf traits (δ 13 C, leaf mass area (LMA)), and canopy defoliation measured after intense drought.  We found significant correlations between PVR and biological variables. For Ψ , the nature and strength of the correlations vary according to the level of drought intensity. The correlation between Ψ and PVR was positive during well-watered conditions in the upper layer (0-2 m) and during water-limited conditions in the deeper layer (2-5 m). During most severe droughts, however, the Ψ was negatively correlated with PVR in the upper layer. Trees with lower PVR in the upper layer were also associated with water use efficiency (higher δ 13 C), higher LMA, and a lower level of defoliation after extreme drought.  Overall, our results indicate that local differences in soil/subsoil properties affect tree response to drought and suggest that less favorable soil/subsoil conditions (lower PVR) can lead to lower water stress during the driest period and to lower defoliation after extreme drought. Plausible explanations for this better acclimation include higher stomatal regulation and improved deep soil and subsoil water exploration by trees located in more adverse conditions. We encourage the development of ERT in ecological studies to further explore the interrelated relationships between soil/subsoil, climate, and tree functioning.

Water ‘on the rocks’: a summer drink for thirsty trees?

“…Karst habitats dominated by shallow soils overlying massive bedrock are challenging for plants, because of limited underground water storage. Roots of woody perennials can grow deeply into cracks and fissures of the bedrock, exploring caves and soil pockets (Nardini et al ., 2016; Savi et al ., 2018; Carriére et al ., 2020; Dawson et al ., 2020). However, not all plant species thriving in rock‐dominated landscapes can rely on deep root systems (Nie et al ., 2014), raising the hypothesis that the bedrock itself represents a water source for vegetation (Liu et al ., 2014).…”

“…In a semiarid environment dominated by Pinus halepensis , mortality risk was highest for trees growing in older‐aged stands on southern aspects (Dorman et al ., 2015). Very local soil and subsoil differences in terms of depth and available water influenced the response to drought of Quercus ilex individuals (Carriére et al ., 2020), leading to differential mortality risk under drought.…”

Understanding Catchment‐Scale Forest Root Water Uptake Strategies Across the Continental United States Through Inverse Ecohydrological Modeling

“…Further, it remains practically difficult to collect and analyze a sufficient number of water isotopic samples to characterize the heterogeneity of soil (e.g., Oerter & Bowen, ) and tree‐stored waters (e.g., Knighton, Conneely, et al, ; Knighton, Souter‐Kline, et al, ). Finally, individual tree responses to drought conditions (Carriere et al, ; Nehemy et al, ) challenge the extrapolation of research findings from the plot to the catchment scale (e.g., Penna et al, ).…”

Exploring Environmental Factors That Drive Diel Variations in Tree Water Storage Using Wavelet Analysis

“…Consequently, there has been increasing interest in electrical resistivity imaging (ERI) to explore the internal properties of trees (Al Hagrey, 2007;Bieker and Rust, 2010;Lin et al, 2012;Guyot et al, 2013;Wang et al, 2016;Benson et al, 2019). ERI is a non-destructive measurement technique that images spatial and temporal variations in bulk electrical conductivity (the reciprocal of bulk electrical resistivity)-a property that can be linked to water moisture inside a tree (e.g., Ganthaler et al, 2019;Carrière et al, 2020). Electrical impedance tomography has also been used successfully to explore the internal properties of trees (e.g., Martin, 2012;Martin et al, 2015;Kessouri et al, 2019).…”