IRCEB: Interannual Climate Variability and Ecosystem Processes: A Quantitative Assessment Combining Modeling with Field and Mesocosm Experiments

Nevada System Of Higher Education, Desert Research Institute, Reno NV

Investigators

Abstract

0078325 Arnone It is well known 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. This IRCEB project has three components - integrating experiments in a unique mesocosm facility, field experiments, and statistical and simulation modeling - that will allow the investigators 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 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 will cause a multitude of ecological responses at different time scales and feedback to affect NEP, and therefore atmospheric CO2. Other feedbacks will be tested, as well. The centerpiece of the 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 on an ecosystem scale while simultaneously controlling climate variables. The EcoCELL experiment involves the imposition of a 4OC 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 the investigators 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 tallgrass prairie experiment in the field and modeling-data synthesis. The tallgrass prairie field study will help to calibrate and scale the observed responses under controlled environments and test causal relationships 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 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 model will represent a range of techniques to identify the processes that control ecosystem responses to temperature anomalies, and allow understanding and development of linkages between the laboratory and field experiments.