Growth and carbon relations of tree line forming conifers at constant vs. variable low temperatures
Article first published online: 24 OCT 2008
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Journal of Ecology
Volume 97, Issue 1, pages 57–66, January 2009
How to Cite
Hoch, G. and Körner, C. (2009), Growth and carbon relations of tree line forming conifers at constant vs. variable low temperatures. Journal of Ecology, 97: 57–66. doi: 10.1111/j.1365-2745.2008.01447.x
- Issue published online: 11 DEC 2008
- Article first published online: 24 OCT 2008
- Received 28 May 2008, accepted 12 September 2008Handling Editor: Matthew Turnbull
- alpine tree line;
- growth-limitation hypothesis;
- Larix decidua;
- non-structural carbohydrates;
- Pinus mugo;
- 1Natural climatic driven tree line positions follow a mean growing season temperature of around 6 °C in seasonal as well as non-seasonal climates. The influence of constant vs. variable temperature regimes on growth was explored by experimentally exposing 2-year-old seedlings of two montane conifer species (Larix decidua and Pinus mugo) to either constant temperatures of 6 °C or 12 °C, or seasonally and diurnally changing temperatures that varied around the same means (covering a 13-K amplitude across the season).
- 2In both species, exposure to 6 °C during a 20-week growing season reduced growth dramatically in constant as well as variable temperature treatments. Nevertheless, new biomass production was still measurable at 6 °C, indicating that a complete cessation of growth occurs at a lower temperature.
- 3The biomass increment by the end of the season was hardly influenced by the presence or absence of temperature variation for both, the 6 °C and 12 °C mean treatments. While seasonal and diurnal variable temperatures had a slightly positive effect on growth compared to a full season at constant temperatures in the deciduous Larix, biomass increments of the evergreen Pinus were the same at constant and variable temperature treatments.
- 4End of season sugar and starch concentrations in different tissues revealed higher concentrations in cold treated seedlings at constant and varying temperatures. In line with previous field data, low temperatures did not lead to carbon depletion (carbon limitation). We thus assume a stronger impact of cool temperatures on meristematic processes (sink activity) than on photosynthesis (source activity).
- 5Synthesis. The similar growth rates of trees in experimentally constant vs. variable growing season temperatures match field observations. Although metabolic responses to temperature are nonlinear, this implies an overall ‘quasi-linear’ response of growth to temperature in trees at their lower temperature limit, which awaits further explanation. The higher concentrations of non-structural carbohydrates in cold treated seedlings support the sink-limitation hypothesis of plant growth in cold climates.