A linear, semi-theoretical relationship between the coverage change of plant communities due to spatial processes and a partial patchiness index of the community distribution patterns in a grassland landscape was established by partitioning the overall coverage change into a spatial increment caused by species migration and a local increment due to local ecological processes. This relationship implies that patchiness of grassland landscapes can accelerate either recovery or degradation of a community, depending on the environmental conditions depicted by a parameter termed as gradient strength. The established relationship also has potential applications in simulating pattern dynamics of plant community distributions for a grassland landscape using a spatially homogeneous patch-scale model. The derived linear relationship was applied to a one-hectare alkaline grassland observatory in northeast China. Gradient strengths of two major plant community types were determined via linear regression from simulation results for selected subregions of the grassland. The calibrated linear relationship was then applied to the rest of the grassland landscape. Preliminary comparisons with complete spatial simulations and observations indicated that using this linear relationship with a patch-scale model can simulate the coverage changes as accurately as using a comprehensive spatial simulation model.

A model of stomatal conductance was developed to relate plant transpiration rate to photosynthetic active radiation (PAR), vapour pressure deficit and soil water potential. Parameters of the model include sensitivity of osmotic potential of guard cells to photosynthetic active radiation, elastic modulus of guard cell structure, soil-to-leaf conductance and osmotic potential of guard cells at zero PAR. The model was applied to field observations on three functional types that include 11 species in subtropical southern China. Non-linear statistical regression was used to obtain parameters of the model. The result indicated that the model was capable of predicting stomatal conductance of all the 11 species and three functional types under wide ranges of environmental conditions. Major conclusions included that coniferous trees and shrubs were more tolerant for and resistant to soil water stress than broad-leaf trees due to their lower osmotic potential, lignified guard cell walls, and sunken and suspended guard cell structure under subsidiary epidermal cells. Mid-day depression in transpiration and photosynthesis of pines may be explained by decreased stomatal conductance under a large vapour pressure deficit. Stomatal conductance of pine trees was more strongly affected by vapour pressure deficit than that of other species because of their small soil-to-leaf conductance, which is explainable in terms of xylem tracheids in conifer trees. Tracheids transport water by means of small pit-pairs in their side walls, and are much less efficient than the endperforated vessel members in broad-leaf xylem systems. These conclusions remain hypothetical until direct measurements of these parameters are available.