Factors Affecting Spatial Variation of Annual Apparent Q10 of Soil Respiration in Two Warm Temperate Forests

A range of factors has been identified that affect the temperature sensitivity (Q(10) values) of the soil-to-atmosphere CO2 flux. However, the factors influencing the spatial distribution of Q(10) values within warm temperate forests are poorly understood. In this study, we examined the spatial variation of Q(10) values and its controlling factors in both a naturally regenerated oak forest (OF) and a pine plantation (PP). Q(10) values were determined based on monthly soil respiration (R-S) measurements at 35 subplots for each stand from Oct. 2008 to Oct. 2009. Large spatial variation of Q(10) values was found in both OF and PP, with their respective ranges from 1.7 to 5.12 and from 2.3 to 6.21. In PP, fine root biomass (FR) (R = 0.50, P = 0.002), non-capillary porosity (NCP) (R = 0.37, P = 0.03), and the coefficients of variation of soil temperature at 5 cm depth (CV of T-5) (R = -0.43, P = 0.01) well explained the spatial variance of Q(10). In OF, carbon pool lability reflected by light fractionation method (L-LFOC) well explained the spatial variance of Q(10) (R = -0.35, P = 0.04). Regardless of forest type, L-LFOC and FR correlation with the Q(10) values were significant and marginally significant, respectively; suggesting a positive relationship between substrate availability and apparent Q(10) values. Parameters related to gas diffusion, such as average soil water content (SWC) and NCP, negatively or positively explained the spatial variance of Q(10) values. Additionally, we observed significantly higher apparent Q(10) values in PP compared to OF, which might be partly attributed to the difference in soil moisture condition and diffusion ability, rather than different substrate availabilities between forests. Our results suggested that both soil chemical and physical characters contributed to the observed large Q(10) value variation.