Abstract: Today research on global change is becoming one of the three vital topics in ecology. Within this field, simulating an individual plant’s physiological responses to global change, especially the combined effects of CO2 enrichment and the climatic change it caused, is a useful model in predicting the changes of either natural vegetation or agricultural crops, in that the physiological basis of the responses are mostly understood and the results of simulation can be checked with experi ments at any level or step when needed. Since the scenarios of the global changes often differ with different GCM’s, and will change as the GCM’s are being improved, even though, the simulation programs can still be used to for new predictions. In this study, based on the physiological mechanisms, a systematic dynamic model of plant individual growth was established, which included a weather generator and a growth module. The combined effects of enriched CO2 and climatic change on the main physiological processes, such as photosynthesis, respiration, etc., and seasonal dynamics of biomass were considered in the model. The data sets of the long-term weather records of Beijing Meteorological Station and the observed values of many ecophysiological quantities, obtained in a CO2 enrichment experiment of soybean, were used to parameterize and to validate the model. The results showed that data obtained from the simulation were quite compatible with those from the observation. When the CO2 concentration was doubled, the peak values of the total biomass and green biomass were increased approximately by 70% and 56% respectively. Furthermore, the responses of the total net assimilation and the average specific dark respiration rate within the growth season explained the internal mechanism of the biomass responses. The result indicated that the total net assimilation increased, while the average specific dark respiration rate decreased. Thus, it can be deduced that the increase of biomass was brought about not only by the increase of the net assimilation, but also by 'the decrease of the specific dark respiration rate. Sensitivity analysis was used to the soybean individual responses to global change. The seasonal dynamics of the total biomass to the combined effects of different levels of CO2, temperature and precipitation were simulated. CO2 concentration and precipitation have positive, while temperature has negative effect on total biomass. The positive effect of precipitation became weaker with increasing temperatures, while the negative effect of temperature was strengthened by the increased precipitation. The positive effect of CO2 concentration became stronger with the increasing temperatures, but weaker under enhancing precipitations. The positive effect of precipitation and the negative effect of temperature were weakened by doubling the CO2 concentration. These are partly due to the enhanced water use efficiency caused by CO2 enrichment, which in turn renders the plant individual more resistant and adaptable to the environmental change.

Key words: Global change, Doubled CO2, Ecophysiology, System dynamics model, Soybean