Precipitation dynamics in a mixed grass prarie: Manipulations and interactions with warming and CO2

Background/Question/Methods

Increased temperatures and altered precipitation regimes will accompany rises in atmospheric [CO₂], and these global changes are likely to have interactive and non-linear impacts on ecosystem processes.  While multi-factor global change experiments are essential for characterizing potential ecosystem responses to future scenarios, a major challenge is placing results in a general, mechanistic framework that explains interannual and diverse responses to different potential scenarios.  Soil water balance is a central factor controlling ecosystem processes, and it is a main driver for understanding ecosystem responses to warming, elevated CO₂, and changing precipitation patterns.  Since 2007, we have measured soil moisture and temperature, evapotranspiration (ET), net ecosystem CO₂ exchange (NEE), and aboveground net primary productivity at the Prairie Heating and CO₂ Enrichment (PHACE) experiment established near Cheyenne, WY USA. This factorial experiment combines FACE (ambient and elevated [600 ppm] CO₂ concentration), experimental warming (1.5¢ªC daytime, 3¢ªC nighttime), and irrigation to evaluate effects of multiple global change drivers on a semi-arid grassland ecosystem.  The ultimate goal of this talk is to understand quantitative and interactive linkages between hydrologic dynamics and ecological processes.  We will address the following specific questions:

1)      How does interannual variability in precipitation interact with warming and elevated CO₂?

2)      Do global changes amplify or reduce variability in available soil water?

3)      How much variability in ecosystem processes can be explained by ecosystem water balance?

Results/Conclusions

In this talk, we will propose a conceptual framework for characterizing climate – soil – ecosystem interactions.  Changes in soil moisture and temperature are essential for understanding the consequences of climate change on plant (growth and physiology) and soil biogeochemical processes.  Synthetic variables that we will use include rain use efficiency and ecosystem water use efficiency and we will explore how they vary in response to elevated CO₂ and warming.