Alternative methods of estimating the water potential at turgor loss point in Acer genotypes

Selecting for drought tolerance in urban tree species can have a significant influence on survival rates, aftercare requirements and performance. The water potential at turgor loss point (π tlp ) is gaining popularity as a trait to help determine drought tolerance to aid tree selection. Therefore, it is important to understand if differing methods used to measure or calculate π tlp deliver consistent results. The sensitivity of three methods used to determine this valuable selection parameter were evaluated. A classical pressure chamber, pressure–volume (P–V) curve method was compared with vapour-pressure osmometer (Vapro ® ) and dewpoint hygrometer (WP4C) methods. These methods were evaluated using closely related cultivars of Acer platanoides and A. pseudoplatanus ‘Negenia’. Both the osmometer and hygrometer methods ranked genotypes with a very high similarity (R s = 1, R 2 = 0.96) and were able to identify significant differences between cultivars. This is the first study to demonstrate suitability of the dewpoint hygrometer in comparison to the vapour-pressure osmometer to measure π tlp . The P–V method was unable to identify differences between the cultivars tested. The Vapro and WP4C provide greater applicability than the conventional P–V method to studies requiring both high throughput and high sensitivity. Consistency of measurement type is however highly recommended in future studies as some differences were observed between Vapro and WP4C.