Seasonal dependence of temperate forest soil respiration to soil temperature and water content clarified through data-driven modeling

Abstract

Soil respiration is commonly modelled as a function of soil temperature and soil moisture, without explicitly accounting for seasonal effects. We have therefore developed a data-driven model that integrates interactions among soil temperature, soil moisture, and seasonality. This model was applied at daily resolution to four years of continuous hourly measurements in a temperate beech forest in northeastern France. Our approach outperforms models that either exclude seasonality or consider only one abiotic factor with seasonal modulation in terms of annual and seasonal carbon budgets, while reasonably capturing the main features of the observed annual cycle. Integrating seasonality with an additional pedoclimatic variable increases the variance of soil respiration explained by fixed effects (from 5% to 34%), suggesting that part of the seasonal variability cannot be captured by instantaneous soil temperature and moisture conditions alone. The model was then used to investigate how pedoclimatic variables control soil respiration across seasons. Results reveal pronounced seasonal variability. Soil respiration increases exponentially with soil temperature in spring under relatively dry soil conditions and in summer and autumn under wetter soils. Conversely, low respiration occurs during summer and autumn when soils are dry and in spring when soils are excessively wet. From spring to autumn, abiotic drivers strongly influence soil respiration, with seasonal shifts in conditions promoting high respiration rates: warm and dry soils in spring versus warm and wetter soils in summer and autumn. The temperature sensitivity of soil respiration (Q 10 ) shows marked seasonal reversals. It decreases with increasing soil moisture in winter and spring but increases with soil moisture in summer and autumn. This indicates that soil respiration is most temperature-sensitive under dry soils in cold seasons and wet soils in warm seasons. Overall, the strong seasonal interactions between soil temperature and moisture, highlight the importance of accounting for seasonality when estimating soil respiration and, subsequently, Q 10 .