Abstract
Boreal tree species are excellent tools for studying tolerance to climate change. Bud phenology is a trait, which is highly sensitive to environmental fluctuations and thus useful for climate change investigations. However, experimental studies of bud phenology under simulated climate change outdoors are deficient. We conducted a multifactorial field experiment with single (T, UVA, UVB) and combined treatments (UVA+T, UVB+T) of elevated temperature (T, +2°C) and ultraviolet‐B radiation (+30% UVB) in order to examine their impact on both male and female genotypes of aspen (Populus tremula L.). This study focuses on the effect of the treatments in years 2 and 3 after planting (2013, 2014) and follows how bud phenology is adapting in year 4 (2015), when the treatments were discontinued. Moreover, the effect of bud removal was recorded. We found that elevated temperature played a key role in delaying bud set and forcing bud break in intact individuals, as well as slightly delaying bud break in bud‐removed individuals. UVB delayed the bud break in bud‐removed males. In addition, both UVA and UVB interacted with temperature in year 3 and even in year 4, when the treatments were off, but only in male individuals. Axillary bud removal forced both bud break and bud set under combined treatments (UVA+T, UVB+T) and delayed both under individual treatments (T, UVB). In conclusion, male aspens were more responsive to the treatments than females and that effect of elevated temperature and UV radiation on bud set and bud break of aspen is not disappearing over 4‐year study period.
Highlights
Global average surface temperatures have increased by 0.85°C over the period from 1880 to 2012 (Intergovernmental Panel on Climate Change (IPCC), 2014)
This study used the same experimental setup as Strømme et al (2015), except that we investigated the subsequent 2-year effects of climate change on P. tremula bud phenology, and the potential carry- over effects for 1 year after the treatments were discontinued
We hypothesized that (i) enhanced temperature will delay bud set and force bud break, while ultravioletB radiation (UVB) will force bud set, and the responses will be mitigated by the experimental years due to acclimation, (ii) the effects of enhanced temperature on bud break will be sustained over the following season, even when the treatments are discontinued, (ii) bud removal will change the growing period due to resource restrictions, and (iv) males and females vary in their responses to the treatments
Summary
Global average surface temperatures have increased by 0.85°C over the period from 1880 to 2012 (Intergovernmental Panel on Climate Change (IPCC), 2014). Strømme et al (2015) have shown that in young P. tremula plantlets, elevated temperature delayed bud set and forced bud break in one growing season old seedlings In their studies, under combined UVB+T treatment, bud set was forced in both males and females while bud break was delayed only in males. We hypothesized that (i) enhanced temperature will delay bud set and force bud break, while UVB will force bud set, and the responses will be mitigated by the experimental years due to acclimation, (ii) the effects of enhanced temperature on bud break will be sustained over the following season, even when the treatments are discontinued, (ii) bud removal will change the growing period due to resource restrictions, and (iv) males and females vary in their responses to the treatments
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