The Labile and Resistant Soil Organic Carbon Pools in the North America Great Plains

Abstract

Among the three major global carbon cycle components, the terrestrial one has been the most uncertain because of the complexity of the soil organic carbon (SOC) dynamics. Previous tracer studies, however, have shown that SOC consists of labile and resistant pools. Labile pools turn over in decades, and resistant pools turn over in hundreds or thousands of years. Labile pools are active in carbon and nutrient cycles and responsive to land-use management changes, whereas resistant pools are less so. Very few studies have actually quantified labile and resistant SOC pools because the isotopic tracer methods, such as the paired-plot bulk-carbon (PPBC) method, can only be applied to a few special cases. I found a study of SOC in the North America Great Plains, in which some of the data are suitable for the PPBC method. The results revealed that the turnover times of the labile SOC pools ranged from 17 years to 93 years, and the sizes ranged from 1.2 g kg−1 to 17.6 g kg−1. The turnover times of the resistant pools ranged from 899 years to 5138 years, and the sizes ranged from 5.0 g kg−1 to 12.4 g kg−1. Land management practices changed the sizes of the labile pools but not their turnover times. This study also pointed out a possibility that allows the application of the PPBC method to a set of much broader cases.