||Our project will assess direct, indirect and interactive effects of elevated CO2 and warming on C metabolism and its components at the Prairie Heating and CO2 Enrichment (PHACE) experiment, with particular emphasis on quantifying the role of soil water availability. To achieve this, we will integrate extensive and diverse field observations from a state-of-the art experiment with process models to address the following objectives:
1) Characterize “fast” processes underlying diurnal to seasonal dynamics of C metabolism components, as driven by soil moisture, temperature, substrate and nutrient availability, plant activity, root and microbial activity, and root-microbe feedbacks such as priming.
2) Characterize “slow” processes underlying interannual and long-term (>5 yr) dynamics of C metabolism components, as driven by precipitation variability, plant community composition, and nutrient status.
3) Evaluate and inform the representation of these slow and fast processes in Earth system models by applying hierarchical Bayesian data-model assimilation methods.
At the PHACE experiment we investigate how multiple global change factors interact to influence a native mixed-grass prairie ecosystem by deploying well-replicated, state-of-the-art Free-Air CO2 Enrichment (FACE) and infra-red warming manipulations. Additional shallow (summer) and deep (spring) irrigation treatments allow evaluation of how seasonality of precipitation influences mixed-grass prairie, and how the magnitude of indirect water effects compares to direct effects of CO2 and warming. To understand mechanisms underlying ecosystem responses, we make extensive use of gas exchange, stable isotope, soil water and nitrogen monitoring, and computer simulation models. Results from the first four years (2006-2009) of manipulations have enhanced mechanistic understanding of ecosystem responses to global changes. This project integrates detailed field experiments with process-based modeling, which is expected to yield a predictive framework for 1) evaluating how changes in water availability control ecosystem responses to other global changes such as elevated CO2 and temperature and 2) quantifying ecosystem responses that cannot be explained by water availability.
This project will provide new information about how increasing atmospheric CO2 and associated climate change alters greenhouse gas emissions and C storage potential of a widespread terrestrial ecosystem.