The effect of contrasting environmental growth conditions (in vitro tissue culture, ex vitro acclimatisation, climate chamber, greenhouse and outdoor) on leaf development, cuticular wax composition, and foliar transpiration of detached leaves of the Populus × canescens clone 84 K were investigated. Our results show that total amounts of cuticular wax increased more than 10-fold when cultivated in different growth conditions, whereas qualitative wax composition did not change. With exception of plants directly taken from tissue culture showing rapid dehydration, rates of water loss (residual foliar transpiration) of intact but detached leaves were constant and independent from growth conditions and thus independent from increasing wax amounts. Since cuticular transpiration measured with isolated astomatous P. × canescens cuticles was identical to residual foliar transpiration rates of detached leaves, our results confirm that cuticular transpiration of P. × canescens leaves can be predicted with high accuracy from residual transpiration of detached leaves after stomatal closure. Our results convincingly show that more than 10-fold increased wax amounts in P. × canescens cuticles do not lead to decreased rates of residual (cuticular) transpiration.

Key message We identified two poplar clones of the same species as highly comparable, yet clones of two further species of the same genus to be distinctly different regarding multiple morphological and ecophysiological traits. Abstract Leaf morphology, wax composition, and residual (cuticular) transpiration of four poplar clones (two clones of the hybrid species P. × canescens, P. trichocarpa, and P. euphratica) were monitored from the beginning to end of the growing season 2020. A pronounced epicuticular wax coverage was found only with P. euphratica. As the most prominent substance classes of cuticular wax primary alcohols, alkanes and esters were identified with P. × canescens and P. trichocarpa, whereas esters and alkanes were completely lacking in P. euphratica. Wax amounts were slightly decreasing during the season and significantly lower wax amounts were found for newly formed leaves in summer compared to leaves of the same age formed in spring. Residual (cuticular) transpiration was about five to tenfold lower for P. × canescens compared with the two other poplar species. Interestingly, with three of the four investigated species, newly formed leaves in summer had lower wax coverages and lower rates of residual (cuticular) transpiration compared to leaves of exactly the same age formed in spring. Our findings were especially surprising with P. euphratica, representing the only one of the four investigated poplar species naturally growing in very dry and hot climates in Central Asia. Instead of developing very low rates of residual (cuticular) transpiration, it seems to be of major advantage for P. euphratica to develop a pronounced epicuticular wax bloom efficiently reflecting light.