Temperature Sensitivity and Basal Rate of Soil Respiration and Their Determinants in Temperate Forests of North China

The basal respiration rate at 10°C (R(10)) and the temperature sensitivity of soil respiration (Q(10)) are two premier parameters in predicting the instantaneous rate of soil respiration at a given temperature. However, the mechanisms underlying the spatial variations in R(10) and Q(10) are not quite clear. R(10) and Q(10) were calculated using an exponential function with measured soil respiration and soil temperature for 11 mixed conifer-broadleaved forest stands and nine broadleaved forest stands at a catchment scale. The mean values of R(10) were 1.83 µmol CO(2) m(−2) s(−1) and 2.01 µmol CO(2) m(−2) s(−1), the mean values of Q(10) were 3.40 and 3.79, respectively, for mixed and broadleaved forest types. Forest type did not influence the two model parameters, but determinants of R(10) and Q(10) varied between the two forest types. In mixed forest stands, R(10) decreased greatly with the ratio of coniferous to broadleaved tree species; whereas it sharply increased with the soil temperature range and the variations in soil organic carbon (SOC), and soil total nitrogen (TN). Q(10) was positively correlated with the spatial variances of herb-layer carbon stock and soil bulk density, and negatively with soil C/N ratio. In broadleaved forest stands, R(10) was markedly affected by basal area and the variations in shrub carbon stock and soil phosphorus (P) content; the value of Q(10) largely depended on soil pH and the variations of SOC and TN. 51% of variations in both R(10) and Q(10) can be accounted for jointly by five biophysical variables, of which the variation in soil bulk density played an overwhelming role in determining the amplitude of variations in soil basal respiration rates in temperate forests. Overall, it was concluded that soil respiration of temperate forests was largely dependent on soil physical properties when temperature kept quite low.