Spatial and seasonal variations of Q₁₀ determined by soil respiration measurements at a Sierra Nevadan forest

We examined the spatial and seasonal variation of Q₁₀ as an indicator of the temperature sensitivity of soil respiration based on field measurements at a young ponderosa pine plantation in the Sierra Nevada Mountains in California. We measured soil CO₂ efflux and soil temperature and moisture in two 20 m × 20 m plots from June 1998 to August 1999. The Q₁₀ values calculated from soil temperature at 10-cm depth ranged spatially from 1.21 to 2.63 among 18 chamber locations in the plots. Seasonally, the Q₁₀ values calculated on the basis of the average soil CO₂ efflux and temperature (10 cm) across the sites could vary from 1.05 to 2.3. Q₁₀ and soil temperature are negatively correlated through a simple linear relationship with R² values of 0.45, 0.40, and 0.54 for soil temperature at 5-, 10-, and 20-cm depth, respectively. However, Q₁₀ and soil moisture are positively correlated with R² values of 0.81, 0.86, and 0.51 for soil temperature at 5-, 10-, and 20-cm depth, respectively. Q₁₀ values derived from temperatures at different soil depths also showed considerable variation along the vertical dimension. Q₁₀ had a large seasonal variation with the annual minimum occurring in midsummer and the annual maximum occurring in winter. Seasonal values of Q₁₀ depended closely on both soil temperature and moisture. Soil temperature and moisture explained 93% of the seasonal variation in Q₁₀. The spatial variation of Q₁₀ had significant influences on the estimation of soil CO₂ efflux of the ecosystem. These variations tended to affect the seasonality of the soil CO₂ efflux more than the annual average. The variations of Q₁₀ and its dependence on soil moisture and temperature have important implications for regional and global ecosystem carbon modeling, in particular for predicting the responses of terrestrial ecosystems to future global warming.