Characteristics of the temperature coefficient, Q10, for the respiration of non-photosynthetic organs and soils of forest ecosystems

Abstract

The temperature coefficient, Q₁₀ (fractional change in rate with a 10vH increase in temperature) describes the temperature sensitivity of soils, roots, and stems, as well as their possible performance in global warming processes. It is also a necessary parameter for the estimation of total CO₂ efflux from each element. A number of studies have focused on Q₁₀ values to date; however, their conclusions are not universal and do not always agree. A review of these reported Q₁₀ values therefore becomes necessary and important for a global understanding of the temperature sensitivity of different forest types and elements. The aims of our present paper are, first, to find the frequency distribution pattern of soils, roots, and stems (branches) and compare their temperature sensitivity; then, to find the Q₁₀ differences between conifer and deciduous tree species and the effect of methodology on Q₁₀ values; finally we want to give a perspective on future Q₁₀-related studies. We found that most Q₁₀ values of each element were concentrated in a relatively narrow range despite a total data distribution over quite a wide range. For soil respiration, the median Q₁₀ value was 2.74 and the center of the frequency distribution was between 2.0 and 2.5 with a percentage of 23%. Most of the data (>80%) were within the range from 1.0 to 4.0. The median Q₁₀ value for root respiration was 2.40 and the center of the frequency distribution was from 2.5 to 3.0 with a percentage of 33%. Most of the results (>80%) ranged from 1.0 to 3.0. For stem respiration, the median Q₁₀ value was 1.91 and the frequency distribution was concentrated between 1.5 and 2.0. Over 90% of the data ranged from 1.0 to 3.0. Obvious differences in Q₁₀ value were found between different elements, stem < root < soil including root < soil excluding root. The differences between woody organisms of stems, roots, and soils excluding roots were statistically significant (p<0.05), indicating that heterotrophic respiration from microorganism activity may be more sensitive to global warming. The duration of the period with leaves slightly affects the temperature sensitivity of woody organisms since the Q₁₀ values for root and stem of coniferous evergreen trees did not differ significantly from deciduous trees (p>0.10). CO₂ analytical methods (soda lime absorption method, IRGA (Infra-read gas analysis), and chromatograph analysis) and root separation methods (excised root and trenched box) slightly affected theQ₁₀ values of soil and root respiration (p>0.10), but an in vitro measurement of stem respiration yielded a significantly higher Q₁₀value than an in vivo method (p<0.05). In general, although the Q₁₀ values of non-photosynthetic organisms stayed within a relatively conservative range, considerable variation between and within elements were still detectable. Accordingly, attention should be paid to the quantitative estimation of total CO₂ efflux by Q₁₀-related models. In future studies, the biochemical factors and the environmental and biological factors controlling respiration should be emphasized for precise estimation of total CO₂ efflux. The difficulty is how to clarify the underlying mechanism for fluctuations of Q₁₀ values for one specific habitat and element (e.g. temperature acclimation or adaptation of Q₁₀ values) and then allow the Q₁₀ values to be more conservative for representation of temperature sensitivity in global warming processes.