Response of juvenile progeny of seven forest tree species and their populations to simulated climate change-related stressors, heat, elevated humidity and drought.

The study aimed to evaluate response and phenotypic plasticity of juvenile progeny of seven forest tree species Pinus sylvestris, Picea abies, Quercus robur, Fraxinus excelsior, Alnus glutinosa, Betula pendula and Populus tremula and their populations to climate change-related stressors, simulated in a phytotron - heat and elevated humidity and heat and drought - in comparison to performance in ambient (control) conditions. Treatment effect on sapling morphometric, physiological and biochemical traits was significant except for health condition, transpiration and photosynthetic rates and water use efficiency (WUE). Species effect and species-by-treatment interaction were strongly significant in most traits studied, indicating a great inter-specific variability of responses to the applied treatments. Compared to control, stem diameter increment was lower for most species following both hot-wet and hotdry treatments, while treatment impact on height increment was less pronounced and sometimes even positive. Drought caused significant defoliation in P. tremula, A. glutinosa and B. pendula, while under hot-wet treatment the defoliation in most species was lower than in control. Following hot dry treatment, WUE in P. abies, P. sylvestris and B. pendula was lower than following both hot-wet treatment and control, while in P. tremula, A. glutinosa and Q. robur WUE was higher. This suggests that the latter species are able to maintain a balance between photosynthesis and transpiration. Photosynthetic rate was highest in P. tremula, B. pendula and A. glutinosa, however it was much more negatively affected by water deficit in these three species than in other tested species. In most cases, drought had a negative effect on production of pigments in deciduous tree species, which, together with increased amounts of malondialdehyde and hydrogen peroxide, indicated a presence of an oxidative stress. Significant population effect and population-by-treatment interactions found for most traits showed different plasticity and response of tree populations to the treatments. Although, only 19% of the populations showed significant ecovalencies. Some of the observed reactions may not be considered as adaptive acclimation as decreasing growth of some species and populations indicates deteriorating performance which may lead to changes in their competitiveness, thus compromising regeneration, persistence of natural successions and sustainability of forest ecosystems. [ABSTRACT FROM AUTHOR]