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Will a warmer climate be too warm to ensure sufficient winter chill to plants?

Periods of cold, dormancy and warmth at the right time: these are the factors that control most Danish fruiting trees and bushes and cause them to thrive and produce fruit and berries. Climate change could put a stopper to that process.

[Translate to English:] Solbær skal helst have kulde og varme på de rigtige tidspunkter for at sætte mange frugter. Foto: Helle K. Sørensen

Fruit trees and shrubs in Denmark and other countries with a temperate climate are programmed to undergo a period of dormancy before they can produce fruit. The seasonal cooling and warming must come at the right times for fruit-setting to function optimally. Global warming, where warming and cooling may come at wrong, unfamiliar times, can upset this system.


Scientists from Aarhus University are leading a new project where they hope to obtain a better understanding of the physiological mechanisms controlling the seasonal adjustments of fruit plants. The knowledge gained can be used in breeding strategies and to ensure that fruit production is optimised to meet higher winter temperatures.


- We would like to understand the physiological mechanisms that operate when higher temperatures alter the cold tolerance and dormancy of plants, and we will identify the properties that make specific varieties more or less vulnerable to higher temperatures, explains project leader, postdoc Majken Pagter. She is currently on leave from her position at Aarhus University in order to work as a postdoc at the Max Planck Institute of Molecular Plant Physiology in Germany. Both institutions collaborate on the project, which is supported by funds from The Danish Council for Independent Research | Technology and Production.


The seasonal cycle is disturbed

Fruiting trees and bushes go through different stages in the course of a year. Autumn is the time when the buds sets, while winter is their resting period. Late spring or early summer is when the blossoming starts. The flowers turn into fruits or berries that are developed over the summer. During the summer and early autumn the fruits ripen and can be harvested and the trees and bushes then again get ready for their winter rest.


Particularly the changes in temperature trigger the seasonal changes in fruit crops in temperate climates. The higher temperatures caused by climate change will likely provoke responses in plants to take place outside the usual seasons. This could be a problem since the right timing of these seasonal events is essential for plant survival, growth and fruit yield.


- Milder winter weather, with a greater risk of a warming of the periods outside the normal season, is likely to affect a number of the reactions of fruit plants, including the development of frost tolerance in the autumn, dormancy in the winter, the loss of frost tolerance in spring and blossoming in summer, says Majken Pagter.


Frost tolerance under the microscope

The scientists will examine how higher temperatures affect the frost tolerance and dormancy period of fruit crops in temperate climates and at what time of the year (autumn, winter or spring) the effect is greatest. The scientists will examine the physiological mechanisms responsible for the change and how higher temperatures affect the interaction between the dormancy period and frost tolerance.


For the experiments the scientists are using a number of different cultivars of blackcurrant bushes. They will be grown outdoors at Aarhus University’s research centre AU Aarslev. In order to increase temperatures by 3-5 degrees in some of the trials, plants will be grown in sheltered spots with heating or in small ceilingless rooms. These plants are compared with plants grown under normal ambient temperatures.


Frost tolerance is associated with a number of physiological and biochemical properties that are likely to be affected by higher temperatures, including respiration, the content and composition of soluble carbohydrates and the activity of enzymes. These properties will be measured in order to come closer to an explanation for the underlying mechanisms governing the seasonal changes. The scientists also measure the frost tolerance, dormancy, flowering and yield of blackcurrant plants.


- A number of experiments have been performed on the effects of climate change on plants, but most have been made in the growing season. There is very little research on the effect of changes to the winter temperatures in a temperate climate. The few studies available indicate that plant response outside the growing season, in other words from late autumn to early spring, may have significant implications for the damage to plants caused by frost, phenology and the distribution and composition of the species. Plant response outside the growing season can therefore have a larger impact on the successful adaptation of temperate plants to climate change than previously thought, says Majken Pagter.


The project has received 2.5m DKK from The Danish Council for Independent Research | Technology and Production.


Further information: Postdoc Majken Pagter, on leave from the Department of Food Science and currently affiliated to the Max Planck Institute of Molecular Plant Physiology until the end of February 2016, e-mail: pagter@mpimp-golm.mpg.de