A source-sink framework for coupling water, carbon, and nutrient dynamics of vegetation.

Feedbacks between photosynthesis and growth and the influence on these relationships of environmental factors are reviewed. The evidence indicates a strong dependence of photosynthesis on photosynthate utilization. It also indicates that growth is more sensitive than photosynthesis to water and mineral nutrient stress. As a consequence, many relationships between photosynthesis and external driving variables are confounded by internal feedback effects that reflect the influence of external factors on growth. A source-sink framework for modeling carbon dynamics with coupled water and nutrient interactions in soil-plant systems is outlined. Simulations based on these concepts suggest that sink feedback regulation of photosynthesis at various times in diurnal, wetting-drying, and annual cycles is probably a common occurrence in soil-plant systems.