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Abstract. Explanations for the occurrence of hysteresis (asynchronicity) between diel soil respiration (R s ) and soil temperature (T s ) have evoked both biological and physical mechanisms. The specifics of these explanations, however, tend to vary with the particular ecosystem or biome being investigated. So far, the relative degree of control of biological and physical processes on hysteresis is not clear for drylands. This study examined the seasonal variation in diel hysteresis and its biological control in a desert-shrub ecosystem in northwest (NW) China. The study was based on continuous measurements of R s , air temperature (T a ), temperature at the soil surface and below (T surf and T s ), volumetric soil water content (SWC), and photosynthesis in a dominant desert shrub (i.e., Artemisia ordosica) over an entire year in 2013. Trends in diel R s were observed to vary with SWC over the growing season (April to October). Diel variations in R s were more closely associated with variations in T surf than with photosynthesis as SWC increased, leading to R s being in phase with T surf , particularly when SWC > 0.08 m 3 m −3 (ratio of SWC to soil porosity = 0.26). However, as SWC decreased below 0.08 m 3 m −3 , diel variations in R s were more closely related to variations in photosynthesis, leading to pronounced hysteresis between R s and T surf . Incorporating photosynthesis into a Q 10 -function eliminated 84.2 % of the observed hysteresis, increasing the overall descriptive capability of the function. Our findings highlight a high degree of control by photosynthesis and SWC in regulating seasonal variation in diel hysteresis between R s and temperature.

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