The Marine Biological Laboratory General Ecosystem Model (MBL-GEM) is a process-based plot-scale model of C-N interactions in terrestrial ecosystems. The original structure of the model is described in detail in Rastetter et al. (1991). Le Dizès et al. (2003) describe the latest version, MBL-GEM III, in detail.
The MBL-GEM III simulates, on an annual time step, plot-level photosynthesis and N uptake by plants, allocation of C and N to foliage, stems, and fine roots, respiration in these tissues, turnover of biomass through litter fall, and decomposition of litter and soil organic matter. The model is generally calibrated to run on mean-July maximum and minimum daily air temperature, mean-July daily irradiance, total growing-season precipitation, mean-annual CO2 concentration, and annual N inputs in deposition. A major feature of the model is that vegetation in the model acclimates to changes in the environment to maintain a nutritional balance between C and N. For example, environmental changes that stimulate photosynthesis (e.g., increased CO2 or higher irradiance) result in an increase in the relative allocation of C and N to fine-root growth, which, in turn, stimulates N uptake. Similarly, environmental changes that stimulate N uptake (e.g., increased available N) increase the relative allocation of C and N to foliage growth, which stimulates C uptake. The C:N ratio of litter determines how it is partitioned among soil organic matter fractions that differ in relative turnover rates. The rates of decomposition and N mineralization also depend upon soil temperature and moisture.
Later modifications to MBL GEM include the incorporation of the Aggregated Canopy Model (ACM, Williams et al., 1997) as the photosynthesis submodel (MBL GEM III), and the conversion to a daily model including a water budget (MBL GEM VI).
Download the Source Code
The full MBL-GEM source code, Windows executables and sample input files, are available for non-commercial use. See the download page for available versions.
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This material is based upon work supported by the National Science Foundation under grants #OPP-9318529, OPP-9732281, DEB-9509613, and DEB-0108960 and the Environmental Protection Agency under grants RFQ-RT-00-00107 and QT-RT-00-001667. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the Environmental Protection Agency.
Last Updated: 1 August 2014 BK