MS Thesis Defense Announcement: Duncan Turley

The CEE Department is pleased to announce Duncan Turley's MS Thesis: "Gauging salinity’s impact on root water uptake and testing for hydraulic redistribution in pecan (Carya illinoinensis) with split-root and sap velocity"

Date: Friday, October 16th, 2026

Time: 9:00 AM

Location: EB 315 or virtually on zoom: https://pdx.zoom.us/u/kcrE3xng6T

Advisor: Dr. Samantha Hartzell

Abstract: "Pecans are a valuable crop with growing regions in the arid to semi-arid climates of the southwestern United States. Due to the region’s low rain and the low water use efficiency of pecan, agricultural farming requires high irrigation inputs (1310 mm per growing season). Pecans are a low salt tolerant crop, and the region has high levels of salinity in the local water sources leading to increased soil salinization and decrease in crop harvests. Hydraulic redistribution is the movement of water through the ground via the comparative water potential gradient highway provided by the plant roots. Pecan has not been tested for this phenomenon and so understanding its ability to move water, particularly in saline environments, could help with improving crop yields as soil salinization increases. This experiment was designed to understand the impact of varied salinity gradients on crop water use with sap flow (internal plant water movement) measured using both temperature dissipation probes and heat ratio methods. Split-rooting and sap flux methodologies are commonly utilized independently for understanding internal water movement and when used in conjunction with soil moisture and matric potential measurements they become powerful tools for those working in environmental fields to learn how plants survive in soils of varied salinity and moisture gradients. Separation of the roots into independent soil compartments that moisture or constituents cannot move between without moving through the plant is split rooting. The selection of the split-rooting method: cutting longitudinal root allowed for the separation of the central thick taproot into two equal sections. After splitting, pecans were tested under saturated, drydown, and two weeks of NaCl treated water with a conductivity of 2 dS m-1. The drydown and salinity treatments did show evidence of hydraulic redistribution via heat ratio method sap flux reporting negative flow during drydown at a magnitude of -0.001 mm s-1, before the salinity uptake during salt treatment prevented hydraulic redistribution appearing to limit nighttime water movement out of the plant. Pecan sap velocity measured using thermal dissipation probes fell with 0.04 – 0.18 mm s-1 which is consistent with existing literature values. Volumetric water content loss in the split tree 1 fell on average 60-70% below reported sap flow in mL per day across all testing periods. The data collected does not conclusively prove or disprove hydraulic redistribution in varied moisture and salinity content soils but does provide some insights into the sensitivity pecans have to spatially heterogeneous changes in water potential gradients."