Synthetic Constraint of Soil C Dynamics Using 50 Years of 14C and Net Primary Production (NPP) in a New Zealand Grassland Site

Time-series radiocarbon measurements have substantial ability to constrain the size and residence time of the soil C pools commonly represented in ecosystem models. 14C remains unique in its ability to constrain the size and turnover rate of the large stabilized soil C pool with roughly decadal residence times. The Judgeford soil, near Wellington, New Zealand, provides a detailed 11-point 14C time series enabling observation of the incorporation and loss of bomb 14C in surface soil from 1959–2002. Calculations of the flow of C through the plant-soil system can be improved further by combining the known constraints of net primary productivity (NPP) and 14C-derived C turnover. We show the Biome-BGC model provides good estimates of NPP for the Judgeford site and estimates NPP from 1956–2010. Synthesis of NPP and 14C data allows parameters associated with the rapid turnover “active” soil C pool to be estimated. This step is important because it demonstrates that NPP and 14C can provide full data-based constraint of pool sizes and turnover rates for the 3 pools of soil C used in nearly all ecosystem and global C-cycle models.