Spatial variability of soil respiration (R _s ) and its controls are subjected to strong seasonality in an even‐aged European beech ( <scp> <i>Fagus sylvatica</i> </scp> L.) stand

Abstract

Abstract Uncertainties arising from the so‐far poorly explained spatial variability of soil respiration (R s ) remain large. This is partly due to the limited understanding about how spatially variable R s actually is, but also on how environmental controls determine R s 's spatial variability and how these controls vary in time (e.g., seasonally). Our study was designed to look more deeply into the complexity of R s 's spatial variability in a European beech even‐aged stand, covering both phenologically and climatically contrasting periods (spring, summer, autumn and winter). Although we studied a relatively homogeneous stand, we found a large spatial variability of R s (coefficients of variation &gt; 30%) characterized by strong seasonality. This large spatial variability of R s suggests that even in relatively homogeneous stands there is a large potential source of error when estimating R s . This was also reflected by the sampling effort needed to obtain seasonally robust estimates of R s , which may actually require a number of samples above that used in R s studies. We further postulate that the effect of seasonality on the spatial variability and environmental controls of R s was determined by the seasonal shifts of its microclimatic controls: during winter, low temperatures constrain plant and soil metabolic activities and hence reduce R s variability (temperature‐controlled processes), whereas during summer, water demand by vegetation and changes in water availability due to the microtopography of the terrain (i.e., slope) increase R s variability (water‐controlled processes). This study provides novel information on the spatiotemporal variability of R s and looks more deeply into the seasonality of its environmental controls and the architecture of their causal‐effect relationships controlling R s 's spatial variability. Our study further shows that improving current estimates of R s at local and regional levels might be necessary in order to reduce uncertainties and improve CO 2 estimates at larger spatial scales. Highlights The spatial variability of soil respiration (R s ) and its environmental controls vary seasonally. Seasonal shifts from temperature‐ to water‐controlled processes determine R s 's spatial variability. Besides microclimate, slope and grass cover explain the spatiotemporal variability of R s . An intense sampling effort is needed to obtain robust R s estimates even in homogeneous forests.