engleski

Impact of drought on leaf phenology and frost susceptibility in a Quercus robur L. provenance test

One of the consequences of climate change in southern and south-eastern Europe is the increased frequency of dry episodes during the vegetation period. Pedunculate oak (Quercus robur L.) is both economically and ecologically important forest tree species that prefer humid habitats. Therefore, knowledge of the impact of drought on this species is of great importance for the adaptation of forestry strategy and practice to changed environmental conditions. In spring 2015, 2-year-old pedunculate oak saplings originated from nine European provenances were used for set up of a provenance trial. The trial was set up according to a split-plot RCB design. Experimental saplings were exposed to drought periods and re-watered afterwards in 2015 and again in 2016, while control saplings were regularly watered. Spring leaf phenology was scored by ordinal scale (1-7) in 2015 (before drought treatment), in 2016 (one year after drought exposure), and in 2017 (after 2 years of induced drought periods). Autumn leaf phenology was scored by ordinal scale (1-5) in 2015 and 2016. The trial was impacted by a late spring frost on April 21st and April 22nd 2017. Frost damage was scored (1 – visible frost injuries on leaves ; 0 – no visible symptoms) on all plants in the trial. Data on leaf phenology were transformed in number of days in a year when a plant reached particular phenophase. ANOVA and Tukey HSD test were used to determine statistical significance of the treatment effect on the provenances. Leaf phenology was significantly influenced by drought in majority of the provenances. Spring phenology was shifted in both years, but in opposite directions. In contrary, autumn leaf phenology was unambiguously shifted towards later senescence. Saplings exposed to drought showed significantly higher susceptibility to the late spring frost in all provenances, but one. The results indicate that differences in frost susceptibility between the provenances were dominantly caused by differences in leaf phenology (i.e. frost avoidance) and less by their active response. Absolutely the most frost-sensitive leafing phase was phenophase 7 and then phase 6 (especially in its more advanced period). Higher susceptibility to the spring frost of the experimental saplings was most probably caused by the leaf phenology shifting (earlier and more advanced leafing - higher sensitivity to the frost). Rare exceptions indicate that resistance to frost may be caused by some kind of molecular response.

carryover effect, drought stress, pedunculate oak, phenology shift, provenance test

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