SAP FLOW, STEM DIAMETER VARIATIONS AND MECHANISTIC MODELLING HAVE POTENTIAL TO ASSESS ROOT PRESSURE

Abstract

Upward water movement in plants via the xylem is generally attributed to transpiration. Under certain environmental conditions also root pressure can contribute to upward xylem water flow as an additional feature. Although the occurrence of root pressure is widely recognized in several plant species, some ambiguity still exists about the exact mechanism behind root pressure, the main influencing factors and the possible consequences. Furthermore, in many horticultural crops, root pressure is thought to cause cells to burst, and as such to have a significant impact on the marketable yield. Despite the big challenges in root pressure research, progress in this area is limited, mostly because of difficulties with direct root pressure measurements. To allow non-destructive and non-invasive estimation of root pressure, we present a new theoretical approach using hypothetic measurements of sap flow and stem diameter variations combined with a mechanistic flow and storage model, based on cohesion tension principles. Transpiration-driven sap flow rates are typically inversely related to stem diameter variations. However, when root pressure is present, the xylem water potential is partly decoupled from sap flow rates and root pressure is consequently reflected in stem diameter variations.