Abstract:

Stem respiration is an important part of the annual carbon balance of forest ecosystems and consumes ca. 11%-33% of total net daytime carbon assimilation. Because of difficulties in measurement, little attention was paid to stem respiration studies in the past. However, with increasing atmospheric CO₂ concentration, studies of stem respiration have become popular. Several methods were applied in earlier studies, including gas exchange measurements and closed method. An open flow system is employed in recent studies. Results from recent research show that the diurnal pattern of stem respiration is bimodal with a midday depression and that rates are the greatest in the growing season. Controlling factors include meteorological factors (e.g., stem temperature, CO₂ concentration and humidity) and biological factors (tree species, tree age, diameter at breast height, sapwood size and nitrogen content in stem). Latitude, altitude and topographic factors indirectly influence respiration rates through meteorological or biological factors, in particular stem temperature. Stem respiration rate is positively correlated with stem temperature. The mechanism of stem respiration and its controlling factors will continue to be subjects of future research. Integration of meteorological and biological factors into models of stem respiration will provide insight into contribution of stem respiration to the carbon balance of forest ecosystems, role of forest ecosystems in reducing CO₂ concentration elevation in the atmosphere, response of forest ecosystems to global changes, and development of carbon cycle models of forest ecosystems. These issues and measurement techniques remain challenging and fruitful areas for future research.

Key words: stem respiration, stem temperature, CO₂ concentration, controlling factor, respiration efflux