Unique responses of respiration, growth, and non-structural carbohydrate storage in sink tissue of conifer seedlings to an elevation gradient at timberline

作者：Bansal Sheel^*; Germino Matthew J

来源：Environmental and Experimental Botany, 2010, 69(3): 313-319.

DOI：10.1016/j.envexpbot.2010.05.002

• Abies lasiocarpa
• Carbon balance
• Pseudotsuga menziesii
• Relative growth rate
• Starch
• Timberline

The role of carbon balance, and particularly carbon sinks, to forest boundaries and climate responses is a major question in forest ecophysiology. At timberline, low-temperature limitations on carbon-sink processes of stem and especially root tissue have been implicated in hypotheses of the upper range limits to tree distributions. Studies on carbon sinks in root and stem tissue of trees at timberline typically report variation in only one carbon sink, such as either growth, respiration, or non-structural carbohydrates (NSCs). However, these carbon sinks may differ in their response to elevation. We asked how three carbon-sink processes in root and stem tissue (i.e. all tissue below the crown of needles) change in conifer seedlings growing from the lower (2450 m) to the upper (3000 m) edges of the timberline ecotone throughout their first growth season. We repeatedly measured respiration (mg(-1) and individual(-1)), growth (relative growth rates [RGR] and biomass), and NSCs in root and stem tissue of Abies lasiocarpa and Pseudotsuga menziesii.
RGR of root and stem tissue were less at the upper compared to lower elevation, but only for the first few weeks of the growing season. Total biomass of root and stem tissue was generally less at the upper site, apparently due to low early season RGR, but ultimately did not significantly differ between sites by the end of the growing season. Unlike growth, respiration rates (mg(-1)) did not differ between elevations during any period of the growing season. Nevertheless, total respiration of CO2 from root and stem tissue (individual(-1)) was 22% less at the upper site, which was attributable to less biomass. NSCs of root and stem tissue, specifically starch, were overall greater at the upper site, particularly for A. lasiocarpa at the end of the season, which did not parallel spatiotemporal trends in growth or respiration. The differences in seasonal trends and the effects of elevation on carbon sinks indicate a degree of independence or uncoupling of growth, respiration, and NSCs of root and stem tissue, which is not commonly appreciated in hypotheses about physiological limitations for trees at timberline. Published by Elsevier B.V.

• 出版日期2010-12