Soil surface CO2 flux as an index of soil respiration in situ: a comparison of two chamber methods
1996
Jensen, L.S. | Mueller, T. | Tate, K.R. | Ross, D.J. | Magid, J. | Nielsen, N.E.
Predictions of global climate change have recently focused attention on soils as major sources and sinks for atmospheric CO2, and various methodologies exist for measuring soil surface CO2 flux. A static (passive CO2 absorption in an alkali trap over 24 h) and a dynamic (portable infra-red CO2 gas analyzer over 1-2 min) chamber method were compared. Both methods were used for 100 different site x treatment x time combinations in temperate arable, forest and pasture ecosystems. Soil surface CO2 flux estimates covered a wide range from 0 to ca. 300 mg CO2-C m-2 h-1 by the static method and from 0 to ca. 2500 mg CO2-C m-2 h-1 by the dynamic method. The relationship between results from the two methods was highly non-linear, and was best explained by an exponential equation. When compared to the dynamic method, the static method gave on average 12% higher flux rates below 100 mg CO2-C m-2 h-1, but much lower flux rates above 100 mg CO2-C m-2 h-1. Spatial variability was large for both methods, necessitating a large number of replicates for reliable field data, with typical coefficients of variation being in the range 10-60%, usually higher with the dynamic than the static method. Diurnal variability in soil surface CO2 flux was partly correlated with soil temperature, whereas day-to-day variability was more unpredictable. However, use of a mechanistic simulation model of CO2 transport in soil, SOILCO2, showed that very large day-to-day changes in soil surface CO2 flux can result from rainfall events causing relatively small changes in soil water content above field capacity (ca. -10 kPa). even if CO2 production rates remained relatively unaffected.
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