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, R² = 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.