Evaluation of Heat Tolerance in Foliar Tissue ofAcerGenotypes

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 8 Acer genotypes ( 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 8 Acer genotypes. 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.