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Research Projects IRCEB: Interannual climate variability and ecosystem processes: A quantitative assessment combining models with field and mesocosm experiments PI: Jay Arnone Project Period: October 2000 - August 2005 Funding: This material is based upon work supported by the National Science Foundation under Grant No. DEB- 0078325 Right: Field excavation of the twelve 12,000 kg intact soil-vegetation monoliths from native Oklahoma tallgrass prairie. |
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Keywords: ecosystem processes, atmospheric CO2, mesocosm experiment, interannual climate variability Project Summary We know that atmospheric CO2 is rising, that changes in atmospheric CO2 are likely to affect the earth's climate, that changes in climate cause changes in net ecosystem productivity (NEP; a measure of ecosystem carbon exchange), and that terrestrial ecosystems act as a regulatory mechanism for atmospheric CO2. Although correlative studies have demonstrated that there are tight connections between atmospheric CO2, climate, and NEP, the fact is that we cannot explicitly quantify the links and feedbacks among them. This is perhaps the most critical void in our knowledge—making it difficult, if not impossible, to predict the rate and consequences of global environmental change. We propose a three-component study—integrating experiments in a unique mesocosm facility, field experiments, and statistical and simulation modeling—that will allow us to explicitly test four hypotheses regarding the relationships among climate, atmospheric CO2, and NEP: (1) an observed rapid rise in global atmospheric CO2 in anomalously warm years results from temperature-induced decreases in NEP resulting from increased heterotrophic respiration (Rh); (2) stimulated Rh (mainly in winter, early spring, and late fall of the warm year) will also lead to increased N mineralization causing increases in available soil N pools which in turn will result in increased plant N uptake and storage; (3) following the warm year, a return to more normal temperatures and Rh levels, along with high plant N stores causing an increase in NPP, will result in a large increase in NEP; and (4) temperature extremes (the anomalously warm year) will cause a multitude of ecological responses at different time scales that feedback to affect NEP, and therefore atmospheric CO2. We will also test other feedbacks (e.g., water availability in the warm year). The centerpiece of our study is an experiment to be conducted in the mesocosm-scale EcoCELL lysimeter laboratory at the Desert Research Institute. This facility has the capability to continuously measure NEP (and related components) on an ecosystem scale while simultaneously controlling climate variables. The EcoCELL experiment involves imposition of a 4°C increase in ambient temperature during the second year of the experiment, which combined with an array of specific measurements to quantify physiological processes that control the carbon cycle, will enable us to understand how NEP responds to year-to-year variation in temperature. Tallgrass prairie, one of the world's most studied grassland ecosystems, provides a model ecosystem for the project; and intact soil-plant monoliths will be extracted from a prairie field site and transported to the EcoCELLs providing the basis for the laboratory test. The EcoCELL experiment will be linked to two other study components, a native tall-grass prairie experiment in the field and modeling-data synthesis. The tallgrass prairie field study will (1) help us calibrate and scale the responses we observe under the controlled EcoCELL environment and test causal relationships of temperature perturbation in a natural setting, and (2) allow manipulative simulation of temperature-induced effects on the availability of soil moisture and nutrients, hypothesized to be key factors in temperature-induced changes in NEP. These experiments will help us determine whether variation in temperature affects tallgrass prairie ecosystem carbon exchange via direct effects, effects on water availability, or effects on nutrient dynamics. Statistical analysis and two specific models will represent a range of techniques to (1) identify the processes that control ecosystem responses to temperature anomalies, and (2) allow us to understand and develop the linkages between the laboratory and field experiments. The overall project objectives are (1) to identify and quantify the linkages between terrestrial ecosystem processes and atmospheric CO2 and (2) to determine how interannual temperature variability impacts these relationships that are important determinants of NEP. |
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