Dependence of the Q10 values on the depth of the soil temperature measuring point

Abstract

The parameter Q 10 is commonly used to express the relationship between soil CO 2 efflux and soil temperature. One advantage of this parameter is its application in a model expression of respiration losses of different ecosystems. Correct specification of Q 10 in these models is indispensable. Soil surface CO 2 efflux and soil temperature at different depths were measured in a 21-year-old Norway spruce stand and a mountain grassland site located at the Experimental Ecological Study Site Bily Kriz, Beskydy Mts. (NE Czech Republic), using automated gasometric systems. A time-delay and goodness-of-fit between soil CO 2 efflux and soil temperature at different measuring depths were determined. Wide ranges of values for the time-delay of CO 2 efflux in response to temperature, Q 10 and the determination coefficient (R 2 ) between CO 2 efflux and temperature were obtained at the both sites. The values of Q 10 and the CO 2 time-delay increased with depth, while the R 2 of the CO 2 -temperature relationship significantly decreased. Soil temperature records obtained close to the soil surface showed the highest values of R 2 and the lowest value of the time-delay at both sites. Measurement of soil temperature at very shallow soil layer, preferably at the soil surface, is highly recommended to determine useable values of Q 10 . We present a new procedure to normalize Q 10 values for soil temperatures measured at different depths that would facilitate comparison of different sites.

Measurement depth effects on the apparent temperature sensitivity of soil respiration in field studies

“…In the study by Perrin et al (2004), the air temperature 9 m above ground level is included and yields a considerably lower value than the three soil temperature series, which are close to each other both in measurement depth and in apparent Q 10 . The study by Pavelka et al (2007), which used the shortest datset, shows an increase only up to a depth of 5 (grassland) or 10 (forest) cm, followed by a decrease for greater depths. Note that Pavelka et al (2007) also provide Q 10 values based on a synchronization of each depth's temperature time series with efflux by crosscorrelation.…”

“…The study by Pavelka et al (2007), which used the shortest datset, shows an increase only up to a depth of 5 (grassland) or 10 (forest) cm, followed by a decrease for greater depths. Note that Pavelka et al (2007) also provide Q 10 values based on a synchronization of each depth's temperature time series with efflux by crosscorrelation. In this case, the apparent Q 10 increases exponentially with depth, reaching an extremely high Q 10 value of 799 in 30 cm depth (grassland).…”

“…Therefore, CO 2 efflux was correlated to temperature values with small amplitude and high phase shift, which can result in very high or very low apparent Q 10 values. The even shorter dataset by Pavelka et al (2007) gives an example of such very low apparent sensitivities at great depths. At the same time, it yields very high values if the synchronization procedure suggested by the authors is applied.…”

“…Davidson et al (1998) predicted that Q 10 values would increase with temperature measurement depth, and recognized that this complicates comparisons between studies. Recently, several field studies with multiple temperature measurement depths have been published (Xu and Qi, 2001;Hirano et al, 2003;Tang et al, 2003;Gaumont-Guay et al, 2006;Khomik et al, 2006;Shi et al, 2006;Wang et al, 2006;Pavelka et al, 2007). All of them show an increase of apparent Q 10 with depth.…”

“…Gaumont-Guay et al (2006) suggest that the temperature-efflux curve with the lowest hysteresis indicates the most appropriate temperature measurement depth. Pavelka et al (2007) also use the maximum R 2 method, but additionally performed a crosscorrelation analysis to align each depths temperature time series with the efflux. Since most studies use a single, more or less arbitrary, temperature measurement depth, the effect of varying temperature measurement depth is often not considered.…”