Insights into trunks of Pinus cembra L.: analyses of hydraulics via electrical resistivity tomography

The lack of elevational changes in electrical resistivity in Pinus cembra trunks indicated consistent growth and hydraulics across elevations. Though, electrical resistivity tomograms exhibited pronounced temperature-driven seasonal changes.

Alpine conifers growing at high elevation are exposed to low temperatures, which may limit xylogenesis and cause pronounced seasonal changes in tree hydraulics. Electrical resistivity (ER) tomography enables minimal invasive monitoring of stems in situ. We used this technique to analyze Pinus cembra trunks along a 400 m elevational gradient up to the timberline and over seasons. Furthermore, ER data of earlywood across tree rings were compared with the respective specific hydraulic conductivity (K _S), measured on extracted wood cores. ER tomograms revealed pronounced changes over the year and a strong correlation between average ER (ER_mean) and air and xylem temperatures. Surprisingly, no elevational changes in ER_mean, earlywood ER or K _S were observed. ER data corresponded to variation in earlywood K _S, which decreased from the youngest (ca. 4-5 cm²s^-1 MPa^-1) to the oldest tree rings (0.63 ± 0.22 cm²s^-1 MPa^-1). The lack of changes in ER data and earlywood K _S along the study transect indicated consistent growth patterns and no major changes in structural and functional hydraulic traits across elevation. The constant decrease in earlywood K _S with tree ring age throughout all elevations highlights the hydraulic relevance of the outermost tree rings in P. cembra. Seasonal measurements demonstrated pronounced temperature effects on ER, and we thus recommend a detailed monitoring of trunk temperatures for ER tomography.