Abstract:

The temperature coefficient, Q₁₀ (Fractional change in rate with a 10 ℃ increase in temperature), can describe the response of organisms to temperature increases as a result of global warming. It is also a necessary parameter for estimating CO₂ efflux. Although many studies have focused on Q₁₀ values, reported values are highly variable. To better understand the sensitivity of forests to global warming, we reviewed and summarized reported Q₁₀ values in the literature. Our specific objectives were the following: 1) to calculate the frequency distribution of Q₁₀ values for soil, tree root and tree stem respiration and compare the temperature sensitivity of these different forest ecosystem compartments; 2) to determine the Q₁₀ values of evergreen and deciduous tree species and examine the methodological influences on their calculation; and 3) to discuss future Q₁₀-related studies. We found that most Q₁₀ values reported for soil, root and stem respiration fell within a relatively narrow range although there were some outliers. For soil respiration, the median Q₁₀ value was 2.74 with 23% of the values falling between 2.0 - 2.5 and 80% falling between 1.0 to 4.0. The median Q₁₀ value for root respiration was 2.40 with 33% of the values falling between 2.5 - 3.0 and 80% between 1.0 - 3.0. The median Q₁₀ value for stem respiration was 1.91 with 90% of the values falling between 1.0 - 3.0. The stem respiration Q₁₀ value was significantly less than both the root and soil respiration Q₁₀ values. There were no significant differences between the Q₁₀ values for root and stem respiration of evergreen and deciduous trees (p>0.10). Methods for CO₂ analysis (Soda lime absorption, IRGA and chromatograph analysis) and root separation methods (Excised root and trenched box) did not have a significant effect on Q₁₀ values of soil and root respiration (p>0.10), butin vitro measurements of stem respiration yielded a significantly higher Q₁₀ value than in vivo methods (p<0.05). In general, although theQ₁₀ values of stem and root respiration fell within a relatively narrow range, there still was considerable variation between and within reported values for stems and roots. More attention should be paid to the quantitative estimation of total CO₂ efflux by Q₁₀ related models. Future research should focus on the biochemical, environmental and biological factors that control respiration for more precise estimation of total CO₂ efflux. The greatest challenge is to better understand the underlying mechanisms that result in the variation in Q₁₀ values between habitats and tree components to make Q₁₀ values more universal for representation of temperature sensitivity to global warming.

Key words: Soil respiration, Stem respiration, Root respiration, Q₁₀ coefficient, Global warming