Using sap flow measurements to estimate net assimilation in olive trees under different irrigation regimes

Abstract

The measurement of bulk net assimilation (A) in fruit tree species is hindered by the need for sophisticated and complex instrumentation. The aim of this study is to present a simple alternative for estimating A from sap flow measurements and meteorological records. The proposed method was tested in a mature hedgerow olive orchard of 22.2 ha. Within the orchard, an irrigation experiment was established in a small plot including three treatments: a full irrigated control (CI), a regulated deficit irrigation (DI) and one additional treatment mimicking the customary orchard irrigation management (FI). Determinations of sap flow, water potential (Ψ) and trunk diameter variations (TDV) were conducted in the three treatments for three years. Also, measurements of net ecosystem exchange (NEE) were performed with an eddy covariance system in the centre of the orchard for the first season. The validity of the method was supported by the fact that our estimates of A were consistent with both the measured values of NEE and published data on the same species under similar environmental and management conditions. Also, differences in A between irrigation treatments were generally coherent with the ones in irrigation applied, transpiration (Ep), Ψ and TDV. It is concluded that the proposed sap flow-based method represents a user-friendly approach to estimate A at the canopy-level with potential to study the effects of deficit irrigation on biomass accumulation.