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Lloyd and Taylor, 1994]. The hypothesis that respiration depends more on temperature than net photosynthesis is crucial for the ecosystem C balance [Kirschbaum, 2000]. This makes investigations on the temperature dependency of C miner- alization very important. The temperature quotient (Q10) describes the ratio of activity for a 10°C (or

10 K) change of temperature. However, there is still no consensus about the form of the relationship between temperature and decom- position [Ka ¨tterer et al., 1998]. The temperature quotient GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 21, GB4017, doi:10.1029/2007GB002983,

2007 1 Institute of Soil Science, University of Hohenheim, Stuttgart, Germany. Copyright

2007 by the American Geophysical Union. 0886-6236/07/2007GB002983 GB4017

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11 (Q10) is often calculated by simple first-order exponential functions yielding a constant Q10 over the investigated temperature range. Q10 values of soil respiration are influ- enced by substrate quality [Fierer et al., 2006;

Mikan et al., 2002]. On the other hand, flexible exponential functions implying greater temperature sensitivity at low temperatures have been found to best describe the temperature response for C or N mineralization over a wide temperature range [Kirschbaum, 1995;

Lloyd and Taylor, 1994]. [3] The temperature dependency of N mineralization is more difficult to investigate because of methodological problems in distinguishing between different soil N turn- over processes. In general, the temperature sensitivity of net N mineralization appeared to be slightly lower than of C mineralization for a wide range of investigated soils [Kirschbaum, 1995]. Kirschbaum [1995], however, pointed out that the high individual range of reported values precludes a final conclusion. Magid et al. [2001] found that the decay of plant residues at low temperatures resulted in a higher proportion of mineralized nitrogen compared with C m........