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Abstract Mean growing season soil PCO 2 data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO 2 ) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO 2 . An improved soil PCO 2 ‐AET model was developed by assuming (1) that as AET approaches zero, soil PCO 2 approaches the atmospheric value and (2) that there is an upper limit to soil PCO 2 at very high AET. This model has the form log(PCO 2 ) = −3·47 + 2·09 (1 −e −0·0172 AET ) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO 2 data, predicts a soil log(PCO 2 ) of − 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO 2 ) = − 1·45) for mean growing season soil PCO 2 at AET values of 2000 mm and above. The results of this study suggest that soil PCO 2 levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.
Brook et al. (Sat,) studied this question.