COS 245-4 - Alpine and Arctic tundra shrub populations show similar ontogenetic growth trends but differing absolute growth rates and lifespan

Background/Question/Methods

The majority of terrestrial primary production is performed by plants, the ontogenetic growth
trends of which greatly influence biomass and carbon dynamics. We study ontogenetic
trends of primary (apical) and secondary (stem thickening) growth in the Arctic (Svalbard,
Norway) and alpine (Krkonoše, Czechia) populations of black crowberry (Empetrum nigrum),
the dominant plant species of certain tundra communities. The environmental conditions in
alpine areas are more favourable for plant growth than those in the High Arctic, where
temperatures are lower, there is less precipitation and soils are shallower, among other
differences. Using dendrochronological methods we sampled two populations from the distinct regions in order to understand the growth ecology (i.e. ontogeny) of this species under diverse environmental conditions.

Results/Conclusions

The differences in the environmental conditions were clearly reflected in significant differences in absolute
growth rates and shrub age between the populations under study. However, we found almost
no differences in ontogenetic growth trends between the populations. In both populations,
primary growth and secondary (stem base) growth decrease over the course of ontogeny
whereas secondary (stem top) growth and basal area increment increase. No significant
differences in the slope of the trends were found in either primary or secondary (stem base)
growth. Trends of the ratio between basal area increment and primary growth revealed neither
absolute nor relative differences between the populations. Ontogenetic trends in the shrubs
analysed were surprisingly stable despite the prominently different environmental conditions.
Empetrum plants have adapted to the different environments by altering their absolute growth
rate only. This adaptation has probably also resulted in the different longevity of plants
constituting the study populations, confirming the theory that slower-growing plants live
longer. Primary growth and secondary (diameter) growth at the stem base seems to be more
basic characteristics of plant growth compared to basal area increment and secondary
(diameter) growth at the apex because the latter two seem to be dependent on the absolute
growth rate.