Long-term validation of continuous measurements of trunk water potential and trunk diameter indicate different diurnal patterns for pear under water limitations

Abstract

Microtensiometers are plant-based sensors than can continuously measure trunk water potential (Ψtrunk). This new water status indicator, Ψtrunk, was compared with the midday stem water potential (Ψstem) measured with a pressure chamber, the current standard for assessing water status in trees, leaf water potential, and maximum daily shrinkage (MDS) in adult 'D'Anjou' pear trees (Pyrus communis L.) irrigated following two strategies, (1) a control treatment (CTL) irrigated at 100% of crop evapotranspiration and, (2) regulated deficit irrigation (RDI). Ψtrunk, Ψstem and MDS were directly influenced by soil water content and atmospheric demand. MDS was able to detect water stress in DI trees the earliest. However, variability was high and it was not sensitive enough to detect significant differences between irrigation treatments at the end of the season. MDS had a maximum value of 300 µm (Ψstem =−1.4 MPa). On the other hand, variation for midday Ψstem and Ψtrunk was low and both indicators were able to distinguish between irrigation strategies. Midday Ψstem and Ψtrunk had a strong linear relationship similar to the identity line (R2 = 0.88). However, when Ψstem and Ψtrunk were compared in the afternoon, Ψtrunk reported by microtensiometers was − 0.7 MPa lower than Ψstem measured by a pressure chamber. The daily relationship between trunk diameter variations and Ψtrunk measured with the microtensiometers followed five different stages. Changes in trunk diameter were delayed relative to changes in Ψtrunk. The seasonal relationship between the MDS and Ψtrunk was strongly related at the start of deficit irrigation (R2 = 0.63), but when the complete season was considered, this relationship was weaker (R2 = 0.44). Moreover, the low coefficient of variation and high sensitivity of the midday Ψtrunk measured with the microtensiometers supports the suitability of using them in automated irrigation systems to monitor tree water status in spite of their high dependence on environmental conditions. This is one of the first studies that validates the use of microtensiometers to continuously monitor tree water status in fruit trees across two consecutive seasons under differing irrigation treatments.

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