A COORDINATION MODEL OF WHOLE-PLANT CARBON ALLOCATION IN RELATION TO WATER-STRESS

Although water is an important determinant of the allocation of materi al between roots and shoots during growth, and often parallels the eff ects of nitrogen, few models have explicitly considered allocation in relation to water supply. We use coordination theory to develop a simp le exponential model that considers allocation of dry matter between s hoots and roots during growth in relation to carbon and water supplies , and accounts for the effects of water stress on growth. We compare c oordination us. optimization (global and local) versions of the expone ntial model by examining similarities and differences in model behavio ur obtained under constant and variable environmental conditions, and with drastically changing conditions (mild, moderate and severe water stress). The greatest differences between coordination and optimizatio n exist in the drastically changing conditions. In a second version of the model, we remove the restriction of exponential growth and show h ow coordination principles can be extended to a more complicated struc ture. The non-exponential model is used to analyse experimental data o n the effects of different pot sizes (and hence water availability) on root restriction and plant growth as reported by Thomas and Strain (P lant Physiology 96: 627-634, 1991). With further refinements, the coor dination model has potential as a tool to model plant growth in relati on to water supply under various environmental conditions. (C) 1997 An nals of Botany Company.