Issues in modelling plant ecosystem responses to elevated CO2 : interactions with soil nitrogen

Models are essential in the study of plant responses to climate change. Most experimental studies are small in spatial scale (individual plants, microcosms, mesocosms) and short in time span (days to years). For example, the largest experimental carbon dioxide concentration ([COz]) studies cover less than l ha and have been 10 years or less in duration (Hendrey eta/., 1999; Ainsworth & Long, 2005). Many science and policy questions that we need to answer, on the other hand, are typically phrased in terms of responses of biomes over several decades: for example, how will crop and forest production be affected in the next 50 years? Will the terrestrial biosphere continue to act as a net carbon sink over the next century? Models are necessary to bridge this gap between experimental and policy time and space scales (e.g. Prentice et al., 2001; Medlyn & McMurtrie, 2005).