A model for the alkaline grassland ecosystems, MAGE, was applied to plant communities dominated by three species. Field observations on two communities dominated respectively by Puccinellia tenuiflora and Suaeda corniculata were used to parameterize the model for multiple species interaction. The model behaves reasonably in following the seasonal variations of water content, soluble sodium cation and calcium cation in surface soil, as well as biomass of the plant communities. Simulations were run to investigate the effects of ground water quality, ground water table depth, maximum noncapillary porosity in surface soil and harvest intensity, on ecosystem dynamics. The results indicated that ground water sodium concentration and ground water table depth had primary control on soil alkalization and vegetation status. The improvement of soil conditions by vegetation is limited to an extent with moderate ground water depth and sodium concentration. Noncapillary pores are critical for vegetation to affect the soil alkalization/dealkalization process, but the effect of noncapillary pores tends to saturate when maximum noncapillary porosity is greater than 0.1.

A stomatal conductance model and a photosynthesis model were applied to field measurements of transpiration and photosynthesis of seven tree species growing in subtropical southern China. Parameter values of drought resistance and tolerance and biochemical assimilation capacity were obtained by means of nonlinear statistical regression, and were used to quantify species succession. The analysis indicated that the models adequately described the ecophysiological behavior of the trees under various environmental conditions. We found a general pattern of decreased drought resistance and tolerance, but increased biochemical assimilation capacity from pines to heliophilus broadleaf trees to mesophilus broadleaf trees. Succession was explained on the basis of these physiological characteristics together with positive feedbacks caused by changes in soil physical properties. The ecophysiological explanation of succession implies that: (1) fitness of a species for a particular succession stage at a particular location can be measured by stomatal behavior and biochemical assimilation capacity under local climate and soil conditions; (2) selection of species for a particular location at a particular succession stage can be guided by the parameter values provided in this study; and (3) succession may be accelerated by selecting trees with large root systems and large soil–root conductances that facilitate soil hydraulic redistribution of water.

A computer simulation model of regional vegetation dynamics was applied to the terrestrial ecosystems of China to study the responses of vegetation to elevated CO2 and global climatic change. The primary production processes were coupled with vegetation structure in the model. The model was parameterized and partially validated in light of a large number of field observations made throughout China on primary productivity, 10 years of monthly meteorological data, 5 years of monthly normalized differential vegetation index observed by NOAA-11 satellite, and digital vegetation and terrain maps. Eight different climatic scenarios, set by perturbations from the present climate, 100% in atmospheric CO2 concentration, 2 C in monthly mean temperature, and 20% in monthly precipitation, were applied to analyze the sensitivity of the Chinese terrestrial ecosystems to climatic change. Simulation results were obtained for each of the climatic scenarios with the model running toward equilibrium solutions at a time step of 1 month. Preliminary validation indicated that the model was capable of simulating the net primary productivity of most vegetation classes and the potential vegetation structure in China under present climatic conditions. The simulations for the altered climatic scenarios predicted that grasslands, shrubs, and conifer forests are more sensitive to environmental changes than evergreen broadleaf forests in warm, wet southeast China and desert vegetation in cold, arid northwest China. For less than 150% of changes in vegetation structure under altered climatic conditions, about three quarters of the changes in net primary productivity of individual vegetation classes were shown to be attributed to the changes in the corresponding distribution area.

The underlying mechanisms of interaction between the symbiotic nitrogen-fixation process and main physiological processes, such as assimilation, nutrient allocation, and structural growth, as well as effects of nitrogen fixation on plant responses to global change, are important and still open to more investigation. Appropriate models have not been adequately developed. A dynamic ecophysiological model was developed in this study for a legume plant [Glycine max (L.) Merr.] growing in northern China. The model synthesized symbiotic nitrogen fixation and the main physiological processes under variable atmospheric CO2 concentration and climatic conditions, and emphasized the interactive effects of these processes on seasonal biomass dynamics of the plant. Experimental measurements of eco-physiological quantities obtained in a CO2 enrichment experiment on soybean plants, were used to parameterize and validate the model. The results indicated that the model simulated the experiments with reasonable accuracy. The R2 values between simulations and observa-tions are 0.94, 0.95, and 0.86 for total biomass, green biomass, and nodule biomass, respectively. The simulations for various combinations of atmospheric CO2 concentration, precipitation, and temperature, with or without nitrogen fixation, showed that increasing atmospheric CO2 concentration, precipitation, and efficiency of nitrogen fixation all have positive effects on biomass accumulation. On the other hand, an increased temperature induced lower rates of biomass accumulation under semi-arid conditions. In general, factors with positive effects on plant growth tended to promote each other in the simulation range, except the relationship between CO2 concentration and climatic factors. Because of the enhanced water use efficiency with a higher CO2 concentration, more significant effects of CO2 concentration were associated with a worse (dryer and warmer in this study) climate.