Productivity and heat-stress tolerance in Canadian poplar (Populus × canadensis Moench) clones with different ecological optimum

Abstract

Cultivation of fast growing poplar (Populus sp.) clones represents an effective means for reaching the 2020 target of the EU-28 renewable energy production. However, considering the continuous climate change, their growth can be markedly affected by summer heat stress episodes in Slovakia. Therefore, in this work two Canadian poplar (Populus × canadensis Moench) clones of different ecological optimum, ‘Gigant' and ‘Pannonia', were investigated in respect of productivity and heat stress tolerance. After three-year cultivation, tree height in the clone ‘Gigant' was 8.9 m, breast trunk diameter 9.3 cm and trunk volume 0.021 m3 compared to 7.9 m, 7.0 cm and 0.012 m3 in clone ‘Pannonia' (despite of relatively more stable trunk growth rate in summer). Trunks of the latter clone contained 12% bark (vs. 10% in ‘Gigant'), 1.5% ash in the wood (vs. 3%) and showed significantly larger wood density (440 vs. 380 kg m−3) but lower wood free energy content (14.5 vs. 16 MJ kg−1). Both of clones were proved to be diploids (2x). Clone ‘Pannonia' exhibited larger heat stress tolerance, as tested in leaves of different developmental stage exposed to 40 °C using chlorophyll fluorescence technique (decreasing from mature to juvenile leaves), lower specific leaf area and higher leaf carotenoid and cytokinin (particularly BAP derivatives) concentration. In spite of lower heat stress tolerance and higher ash content, clone ‘Gigant' showed larger productivity than clone ‘Pannonia', suggesting potential of the latter for cultivation in much more stressful conditions.