Quantifying turgor loss point and leaf water potential across contrasting Eucalyptus clones and sites within the TECHS research platform

Abstract

Understanding the mechanisms governing drought tolerance in highly productive clonal Eucalyptus plantations in Brazil will become increasingly important with climate change driven increases in temperature and drought events. We quantified how leaf water potential, hydraulic safety margin (mid-day – pre-dawn leaf water potential, Ψδ) and the physiological parameters obtained from standard pressure–volume curves differed between four contrasting Eucalyptus genotypes across a temperature and water availability gradient in Brazil. We hypothesized that genotypes developed in dry areas were more drought tolerant and would exhibit lower mid-day leaf water potentials and turgor loss points than clones developed in wetter regions. Recognizing that standard pressure volume curves are time consuming and may not be a suitable screening tool for forest managers, we also tested if a key physiological parameter from the pressure–volume curve (turgor loss point, πtlp) could be accurately estimated from an osmometer as has been found in other species. We found no support for our first hypothesis; physiological parameters determined (including turgor loss point) from the pressure volume curves were not associated with the supposed drought tolerance of any of the clones. Similarly, mid-day leaf water potentials were not directly correlated with drought tolerance. The lack of support for our hypothesis may be because our measurements were taken during periods of minimum water stress. However, we did find that, overall, turgor loss point tended to be lower at the dry compared to wetter sites we studied suggesting that it may be a useful tool for assessing drought tolerance of Eucalyptus plantations in the future. We also found that estimates of osmotic potential at full turgor were similar between the pressure volume curve and osmometer techniques and that turgor loss point can be accurately estimated with an osmometer in highly productive Eucalyptus genotypes (R2 = 0.79).