Abstract
Abstract. CO2 efflux at the soil surface is the result of respiration in different depths that are subjected to variable temperatures at the same time. Therefore, the temperature measurement depth affects the apparent temperature sensitivity of field-measured soil respiration. We summarize existing literature evidence on the importance of this effect, and describe a simple model to understand and estimate the magnitude of this potential error source for heterotrophic respiration. The model is tested against field measurements. We discuss the influence of climate (annual and daily temperature amplitude), soil properties (vertical distribution of CO2 sources, thermal and gas diffusivity), and measurement schedule (frequency, study duration, and time averaging). Q10 as a commonly used parameter describing the temperature sensitivity of soil respiration is taken as an example and computed for different combinations of the above conditions. We define conditions and data acquisition and analysis strategies that lead to lower errors in field-based Q10 determination. It was found that commonly used temperature measurement depths are likely to result in an underestimation of temperature sensitivity in field experiments. Our results also apply to activation energy as an alternative temperature sensitivity parameter.
Highlights
Soil respiration is increasingly recognized as a major factor in the global carbon cycle
Graf (a.graf@fz-juelich.de) ically, the temperature sensitivity of soil respiration is expressed as the Q10 value, i.e. the factor by which respiration is enhanced at a temperature rise of 10 K (Appendix A)
CO2 efflux was correlated to temperature values with small amplitude and high phase shift, which can result in very high or very low apparent Q10 values
Summary
Soil respiration is increasingly recognized as a major factor in the global carbon cycle. In most field studies, columnintegrated soil respiration and its sensitivity are quantified by a single temperature measurement, while the total flux is a sum of source terms from various depths, which are exposed to different temperature regimes. Because of the attenuation and phase shift of temperature fluctuations with increasing depth, the apparent Q10 will depend on the temperature measurement depth. This possibility was mentioned first by Lloyd and Taylor (1994), but without quantification. Davidson et al (1998) predicted that Q10 values would increase with temperature measurement depth, and recognized that this complicates comparisons between studies. In a laboratory incubation, Reichstein et al (2005a) found strongly differing temperature time series between two probe locations within the soil core, and used a multiple regession to consider both locations as sources
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