Root system architecture in relation to life history and nutrient supply

Extreme topologies for root systems can be viewed either as minimizing cost or maximizing efficiency of soil exploration. Plants of red clover Trifolium pratense L., lettuce Lactuca sativa L., four species of Festuca and three of Geranium were grown in a range of nutrient supply conditions, to test this hypothesis. Topology was generally insensitive to changes in the supply of N and P but large differences between species were found: slow-growing perennials had efficient, herring-bone systems, whereas annuals were at the opposite extreme. This accords with earlier predictions. Lengths of external links were reduced by N and of internal links by P. There were large differences between species in mean link lengths. These data confirm the value of topological analyses in understanding the functional architecture of root systems.