The Seasonal Soil Respiration-Temperature Hysteresis Relation Regulated by Photosynthesis and Soil Moisture

Soil respiration responds to temperature in an exponential manner across most ecosystems, but pronounced seasonal respiration-temperature hysteresis relations have been commonly reported in field measurements, with the underlying mechanisms remaining unclear. Our poor understanding to such hysteresis limits the ability to accurately simulate soil respiration. Here, we applied both numerical analysis and field measurements across various ecosystems, to identify the underlying mechanism. We used numerical model runs to show that both photosynthesis and soil moisture contribute to the formation of the hysteresis, supported by field measurements. A time lag between seasonal photosynthesis and soil temperature series plays an important role in decoupling soil respiration from temperature, providing one reason of the hysteresis. Specifically, the total soil respiration-temperature hysteresis is in clockwise direction when seasonal temperature lags behind photosynthesis, and in counterclockwise direction when photosynthesis lags behind soil temperature. Cross sites analysis shows that the time lag of respiration and temperature correlates linearly with that of photosynthesis and temperature (regression function: y=1.11x-2.35, R2=0.86, p<0.05). But when photosynthetic input to belowground is eliminated at a girdling experiment, no hysteresis emerge in the soil respiration-temperature relation, because the time lag of respiration and temperature is suppressed. In water limited ecosystem, soil moisture becomes the dominant factor of soil respiration so that the time lag between soil moisture and temperature provides another reason of the seasonal hysteresis.