Abstract
Global climate models predict an increase in the mean surface air temperature, with a disproportionate increase during winter. Since temperature is a major driver of phenological events in temperate woody perennials, warming is likely to induce changes in a range of these events. We investigated the impact of slightly elevated temperatures (+0.76 °C in the air, +1.35 °C in the soil) during the non-growing season (October-April) on freezing tolerance, carbohydrate metabolism, dormancy release, spring phenology and reproductive output in two blackcurrant (Ribes nigrum) cultivars to understand how winter warming modifies phenological traits in a woody perennial known to have a large chilling requirement and to be sensitive to spring frost. Warming delayed dormancy release more in the cultivar 'Narve Viking' than in the cultivar 'Titania', but advanced budburst and flowering predominantly in 'Titania'. Since 'Narve Viking' has a higher chilling requirement than 'Titania', this indicates that, in high-chilling-requiring genotypes, dormancy responses may temper the effect of warming on spring phenology. Winter warming significantly reduced fruit yield the following summer in both cultivars, corroborating the hypothesis that a decline in winter chill may decrease reproductive effort in blackcurrant. Elevated winter temperatures tended to decrease stem freezing tolerance during cold acclimation and deacclimation, but it did not increase the risk of freeze-induced damage mid-winter. Plants at elevated temperature showed decreased levels of sucrose in stems of both cultivars and flower buds of 'Narve Viking', which, in buds, was associated with increased concentrations of glucose and fructose. Hence, winter warming influences carbohydrate metabolism, but it remains to be elucidated whether decreased sucrose levels account for any changes in freezing tolerance. Our results demonstrate that even a slight increase in winter temperature may alter phenological traits in blackcurrant, but to various extents depending on genotype-specific differences in chilling requirement.
Highlights
Global climate models predict an increase in the mean surface air temperature, frequency and severity of erratic temperature events during this century
Our study has documented that even mild winter warming modifies phenological traits of blackcurrant, but the magnitude of the responses varies between genotypes differing in chilling requirement
The response to warming was greater in spring than during the dormancy phase in both cultivars, but since warming predominantly advanced spring phenology of the relatively low-chilling-requiring genotype ‘Titania’, it is likely that in even warmer winters the response during the dormancy phase will override spring phenological advances in genotypes with large chilling requirements (e.g. ‘Narve Viking’)
Summary
Global climate models predict an increase in the mean surface air temperature, frequency and severity of erratic temperature events during this century. Within Europe, temperatures are predicted to increase disproportionately during winter (Christensen et al 2007; Gu et al 2008). Since temperature is a major driver of phenological events in temperate woody perennials (Fitter and Fitter 2002; Parmesan 2006), milder weather during the colder periods of plants’ annual cycle is likely to induce changes in a range of these events. The magnitude of winter climate change effects on phenological traits may have broad implications for the structure and functioning of forest and landscape ecosystems and the sustainability of horticultural production systems
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