Soil respiration is one of the most important components of the carbon cycle in terrestrial ecosystems, and its response to temperature change has dramatic effects on the feedback between terrestrial carbon cycle and global warming. Our understanding of the impact of environmental and biological factors on soil respiration has been enhanced greatly recently, however our knowledge on the temperature sensitivity of soil respiration is still very limited. Therefore it is critical to have deeper understanding of the factors that control the temperature sensitivity of soil respiration. In this paper we reviewed the recent studies about the temperature sensitivity of soil respiration. We found that soil organisms, substrate availability and quality had significant effects on the temperature sensitivity of soil respiration, but the results of most studies were incompatible. Activation energy theory suggests that the temperature sensitivity of soil respiration should increase with decreasing substrate quality. However, this hypothesis received dramatic challenge. Based on Michaelis-Menten function, theoretic and experimental results showed that substrate availability had a significant positive effect on temperature sensitivity. Consequently results from previous research indicated that the temperature sensitivity of resistant substrates may be greater than, equivalent to, or less than that of labile substrates. One can not explain the difference among various experiments without taking biological factors into consideration. For example, temperature change has great influence on root biomass, soil microbial population structure and biological diversity, which may alter the response of soil respiration to temperature change. Temperature sensitivity is high when root growth and temperature increasing occurred synchronously. Similarly it will be low when they occurred asynchronously. At ecosystem and regional scales, temperature and moisture were main factors affecting the temperature sensitivity of soil respiration, ie Q₁₀ value negatively and positively related with temperature and moisture, respectively, except for too dry or too wet conditions.
In addition, we also compared the literatures and pointed out the sources of uncertainties. Because of the time lag and attenuation, the temperature sensitivity of soil respiration strongly depends on the temperature measuring depth. In order to reduce uncertainties, the effect of varying temperature measurement depth must be considered and most appropriate temperature measurement depth must be selected. Research scales should also be taken into consideration. Since soil respiration measured at various temporal and spatial scales reflect diverse processes, its temperature sensitivity was dominated by different factors. The responses of root respiration and microbial respiration to temperature change may be different, which is also a source of uncertainty. For example, some studies found root respiration was more temperature sensitive than microbial respiration when measured during the course of a year, and this high temperature sensitivity was controlled by substrate supply from photosynthesis, which means the proportion of root respiration to microbial respiration is one of the reasons causing higher variability. Rhizosphere priming effect can also obscure the temperature sensitivity of soil respiration. In fact, the rhizosphere priming effect is of key importance to our understanding of soil respiration, because it means that the total soil respiration is not a simple additive function of soil-derived and plant-derived respiration.
Finally, based on our thorough review, three priority areas on temperature sensitivity of soil respiration are proposed as follows: (1) the difference of the temperature sensitivity between root respiration and microbial respiration; (2) interaction effects between substrate quality and substrate availability on the temperature sensitivity; and (3) the influences of biotic factors (plant root and microbial structure) on temperature sensitivity of soil respiration.