Evaluation of Heat Tolerance in Foliar Tissue ofAcerGenotypes

Abstract Background Extreme summer heat events in which temperatures exceed 40 °C are expected to increase in duration and intensity worldwide. Consequently, selecting heat-tolerant trees for future predicted climatic conditions will be one of the significant challenges for urban landscape managers. Method The effect of heat stress (44 °C for 4 hours) on chlorophyll variable:maximum fluorescence (Fv/Fm) ratios and Soil Plant Analysis Development (SPAD) values as measures of damage to the leaf photosynthetic system and leaf chlorophyll content was quantified in 8Acergenotypes (Acer pseudoplatanus‘Negenia’,A. pseudoplatanus‘Spaethii’,A. platanoides‘Royal Red’,A. platanoides‘Princeton Gold’,A. platanoides‘Emerald Queen’,A. platanoides‘Drummondii’,A. campestre,A. campestre‘Louisa Red Shine’). Results Fv/Fm ratios proved to be a sensitive indicator of heat damage and positively identified marked differences in tolerance to and recovery from heat damage between the 8Acergenotypes. Estimated leaf chlorophyll content (SPAD) was not sufficiently sensitive to distinguish differences in tolerance and recovery between genotypes. Conclusions Chlorophyll fluorescence Fv/Fm ratios, but not estimated leaf chlorophyll content (SPAD), offers a rapid screening technique for assessing the tolerance to and recovery from heat stress in leaf tissue of trees.