Belowground limitation and forest carbon sinks
Predicting the behavior of plants in the face of the novel environmental changes that come with elevated CO2 and climate change is a difficult task. Plants are complex systems whose behavior often depends on several interacting components. To further our mechanistic understanding of forest carbon sinks and build predictive models of them in the future, we combine simplified theoretical models with experimental and observational data. With understanding from these theoretical/empirical comparisons, we then scale up plant responses using an Earth System Model (LM3V/PPA).
In this poster, we present the insights from empirical/theoretical comparisons and show progress on incorporating these into an earth system model. We find that forest responses to elevated CO2 alone include increases in carbon storage whether plants are limited by water, nitrogen or both. Changes in relative allocation among tissues, specifically from short-lived fine-roots to long-lived woody biomass, amplify carbon sinks if water limitation is alleviated by the elevated CO2. These responses are consistent with dominant variation in allocation patterns in forests across the globe as well as experimental plant responses to resource additions. Further, the response of sustained elevated NPP despite nitrogen limitation in FACE experiments is explained by the predicted shifts in carbon and nitrogen allocation in plants following CO2 addition. Finally, observations show that across the globe water use efficiency is increasing, however growth rates of those forests may increase or decrease. This is consistent with the hypothesis that changing climatic factors including rainfall regime may be more important that increasing CO2 for the overall changes in carbon storage in forests.