Root system topology of plants from habitats differing in soil resource availability

1. We examined the branching patterns of plant root systems to test the expectation that these differ both in a species-specific fashion in species from habitats differing in soil resource availability and as a plastic response to varying resource levels. 2. We grew 17 species of winter annual plants in a common greenhouse environment at two soil resource levels. Water and all nutrients were varied in tandem. The species were from collections made at two stabilized sand dune sites in Israel; one a resource-poor desert site, the other a relatively rich mediterranean site. 3. Branching pattern was quantified by Fitter's altitude topological index. High values of this index indicate a herringbone branching pattern, with root systems consisting of a main axis and primary laterals only. Low values indicate a more dichotomous branching pattern. 4. Dicots showed the predicted plastic response, tending towards more herringbone root systems with decreased resource availability. Dicots from the lower-resource desert site had more herringbone root systems than those from the richer mediterranean site, although this difference was significant only when the species were grown under low-resource conditions. 5. Grasses were relatively invariant, with close to maximally herringbone topology and did not show any significant plastic response or differences between species of different habitats.