2.01.14 - Cold and drought hardiness


Totte Niittylä, Sweden


Kaisa Nieminen, Finland

About Unit

IUFRO Working Party 2.01.14 is concerned with the biological basis of resistance to low temperature and drought in forest trees. Adaptation to the cold season is essential for northern trees and trees at high altitudes, whereas drought is a major stress factor to southern trees, especially in regions with a Mediterranean climate. It goes without saying that these stress factors need to be addressed whenever planning forest management practices with tree species exposed to the stress factors. Furthermore, due to climate change the seasonality and severity of both stress factors will alter in the future. This will expose the trees to novel combinations of environmental factors some of which may not have existed before during the entire evolutionary history of the trees. In this way climate change will constitute a new challenge, first of all to the trees, but also to tree ecophysiologists studying the climatic adaptation of the trees.

State of Knowledge

Traditionally, the tree adaptation to cold and drought has been studied at the whole tree and cellular levels. Several physiological mechanisms of the adaptation, such as the dehydration of cells during frost hardening and closing of stomata during drought, have been understood quite well already for decades. Similarly, many aspects of the environmental regulation of the annual development of the trees, such as chilling requirement of dormancy release, are well documented. Mathematical modelling has become an important tool for the studies carried out at the whole tree level, especially when addressing the effects of climate change. Despite all this progress, however, several aspects of the tree adaptation remain enigmatic. For instance, quite little is still known about the physiological mechanism of dormancy release caused by chilling.

Recently, the tree adaptation to cold and drought has been studied more and more at the molecular level. Several groups have used technologies such as microarrays to perform global transcript profiling and identified gene expression networks associated with cold hardiness in trees. At the transcriptional level, several of the factors that regulate the expression of cold hardiness related genes appear to be conserved between model plants such as Arabidopsis and trees such as poplar and birch allowing the use of information from the model plants to trees. At the same time it appears that there are significant differences between trees and Arabidopsis e. g. the regulation of cold hardiness by day length signals that is beginning to be elucidated recently at the molecular level. With the possibility of genetically manipulating trees such as poplar the validation of hypothesis and identification of candidate genes involved in regulating cold hardiness is becoming possible and one expects several novel aspects of cold hardiness being discovered in tree species in the near future. A great advantage of the molecular research on cold hardiness in tree species now also opens up the possibility to study the effect of climate change on adaptation in tree species using molecular tools.

The two schools of studies on tree adaptation to environmental stresses have remained somewhat isolated from each other. It is obvious that considerable advances in our understanding would be achieved with a closer co-operation between researchers working on the whole tree / cellular level and on the molecular level. Facilitating this kind of co-operation is the main goal of our Working Party.