Abstract
Prognostic and mechanistic schemes for the determination of plant phenological stages
from environmental conditions and for the estimation of net primary production (NPP) are presented.
The new schemes account for different biomes and are included in a global model of carbon cycling in
the terrestrial biosphere The capability of such a model to simulate the seasonal cycle of atmospheric
CO2 is explored. The model is forced by mean monthly climate variables (temperature, precipitation
and light) and the mean annual CO, concentration. It predicts atmosphere-biosphere CO2 exchange
fluxes, leaf area index (LAI),a nd the times of budburst and leaf abcission. The predicted variables can
be validated against data on the observed annual cycle of atmospheric CO, concentration and against
observations of LA1 derived from satellite data. The estimated annual NPP of forests appeared realistic;
however, the NPP of grass-dominated biomes was greatly underestimated. This seems to be related to
the fact that belowground biomass is not explicitly considered in the model. The results of a simulation
of the seasonal cycle of atmospheric CO2 concentration using a S-dimensional atmospheric transport model were in satisfactory agreement with the observations.
