Physiological Behaviour and Growth Responses of Eucalyptus camaldulensis Dehn. Seedlings to Salt Stress Conditions

Soil salinity is a critical global problem, especially in arid and semi-arid regions. In such regions soluble salts accumulate in the soil since precipitation is greatly outweighed by evaporation. Eucalyptus camaldulensis is an important forest tree species, which is of high productivity in a relatively short rotation and is extensively grown in irrigated plantations in many parts of the globe. In the present work our main goal is to evaluate the sensitivity and growth performance of E. camaldulensis under salt stress conditions. E. camaldulensis seedlings (shoot height 32.4 0.87 cm) were subjected to a relatively wide range of salt stress 0 (control), 30, 50, 80 and 100 mM NaCl for four weeks under nursery conditions. Growth performance (shoot height, stem diameter and leaf formation rates) was regularly monitored twice a week. At harvest, each plant was separated into root and shoot systems to evaluate the effect of the salt treatment on dry mass production, accumulation and partitioning. Initially, growth was unaffected by salt treatments until the second week. However, significant reductions were observed towards the end of the exposure period. Among the growth parameters analyzed leaf formation rate was the most sensitive compared to stem height and stem diameter growth rates. Dry mass showed significant reductions in both shoot and root especially in plants that received the highest salt concentrations. Based on these results it might be suggested that E. camaldulensis is sensitive to salt stress and is rather unsuitable tree species to be used in sites affected by high levels of salinity. Since leaf formation is tightly associated with shoot apical meristem activity, the current findings obviously points to a link between salinity and plant hormone status. Therefore, it would be helpful to conduct further experiments including some hormone analysis to validate these speculations and to find explanations for the physiological events responsible for the poor performance of E. camaldulensis under saline soils.