Submitted to: Ecological Modeling
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/25/2010
Publication Date: 1/1/2011
Citation: Manzoni, S., Katul, G., Fay, P.A., Polley, H.W., Porporato, A. 2011. Modeling the vegetation-atmosphere carbon dioxide and water vapor interactions along a controlled CO2 gradient. Ecological Modeling. 222:653-665. Interpretive Summary: Field experiments designed to study effects of rising atmospheric CO2 and other aspects of climate change on ecosystem structure and function are well controlled and allow precise application of treatments, but are often limited in the number of treatments that can be imposed. Numerical simulation models can overcome this limitation by simulating the effects of experimental treatments beyond that which can be implemented in field experiments. This paper describes a model providing these capabilities to the Lysimeter CO2 gradient experiment. Here is the model is described in detail, and evidence is presented showing that the model does a good job of reproducing key ecosystem properties documented in the experiment. The model will be very useful for studying effects on grassland carbon cycling of varying temperature and precipitation patterns that cannot be applied to the actual field experiment.
Technical Abstract: Ecosystem functioning is intimately linked to the physical environment by complex two-way interactions. These two-way interactions arise because vegetation both responds to the external environment and actively regulates its micro-environment. By altering stomatal aperture, for example, plants modify soil moisture and atmospheric humidity and these same physical variables, in return, modify stomatal conductance. Relationships between biotic and abiotic components are particularly strong in closed, managed environments such as greenhouses and growth chambers, which are used extensively to investigate ecosystem responses to climatic drivers (e.g., elevated CO2 concentration). Model-assisted designs that account for the physiological dynamics governing two-way interactions between biotic and abiotic components are absent from many ecological studies. Here, a general model of the plant-atmosphere system in closed environments is proposed. The model accounts for linked carbon-water physiology, turbulent transport processes, and energy and radiative transfer principles. Leaf gas exchange is modeled using a C gain optimization approach that is coupled to leaf energy balance and two-dimensional scalar turbulent transport within the canopy. As a case study, the model is parameterized using the Lysimeter CO2 Gradient (LYCOG) facility, wherein a continuous gradient of atmospheric CO2 is maintained on grassland assemblages using an elongated chamber. The model is employed to investigate how species composition and climatic conditions affect the CO2 concentration gradient within the LYCOG where the microclimate is regulated by variation in air flow rates. The sensitivity of the model to key physiological and climatic parameters allows it to be used not only to manage current experiments, but to formulate novel ecological hypotheses (e.g., by simulating climatic regimes not currently employed in LYCOG) and suggest alternative experimental designs and management strategies.