Large seasonal changes in Q10 of soil respiration in a beech forest

We analyzed one year of continuous soil respiration measurements to assess variations in the temperature sensitivity of soil respiration at a Danish beech forest. A single temperature function derived from all measurements across the year (Q(10) = 4.2) was adequate for estimating the total annual soil respiration and its seasonal evolution. However, Q(10)'s derived from weekly datasets ranged between three in summer (at a mean soil temperature of 14degreesC) and 23 in winter (at 2degreesC), indicating that the annual temperature function underestimated the synoptic variations in soil respiration during winter. These results highlight that empirical models should be parameterized at a time resolution similar to that required by the output of the model. If the objective of the model is to simulate the total annual soil respiration rate, annual parameterization suffices. If however, soil respiration needs to be simulated over time periods from days to weeks, as is the case when soil respiration is compared to total ecosystem respiration during synoptic weather patterns, more short-term parameterization is required. Despite the higher wintertime Q(10)'s, the absolute response of soil respiration to temperature was smaller in winter than in summer. This is mainly because in absolute numbers, the temperature sensitivity of soil respiration depends not only on Q(10), but also on the rate of soil respiration, which is highly reduced in winter. Nonetheless, the Q(10) of soil respiration in winter was larger than can be explained by the decreasing respiration rate only. Because the seasonal changes in Q(10) were negatively correlated with temperature and positively correlated with soil moisture, they could also be related to changing temperature and/or soil moisture conditions.