Modelling root architecture: are there tradeoffs between efficiency and potential of resource acquisition?



A model is presented that examines the role of variations in the size of root systems as well as size-independent aspects of architecture on both the efficiency (volume of soil exploited per unit volume of root) and potential of exploitation (volume of soil exploited). This model is unique in that it explores the architecture of actual root systems rather than statistical approximations of root systems. This design allows the assessment of variations m root system size and size-independent aspects of architecture in realistic covarying combinations. Root systems of Senecio vulgaris L. grown in ambient and double-ambient atmospheric CO2 concentrations and two watering regimes were used to parameterize the model.

There was a clear trade-off between the efficiency and potential of exploitation. Large root systems showed high exploitation but low exploitation efficiency. Inversely, small root systems showed low potential and high efficiency. Overall, the potential of soil exploitation was more strongly correlated with all measured aspects of root architecture than was efficiency. Root system size (total length or number of root tips) was much more highly correlated with patterns of soil exploitation, efficiency and potential, than were size independent aspects of architecture. These findings art important to studies of root architecture, demonstrating that studies of root system architecture need simultaneously to measure root system size, size-independent aspects of architecture and in situ patterns of deployment (e.g. trajectories of growth) to understand the functional significance of root architecture.