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Keywords:

  • clonal plants;
  • foraging;
  • morphological plasticity;
  • patch selection;
  • root : shoot ratio

Summary

1  We report on an experimental investigation into the effects of contrast in patch quality and patch size upon the performance of the clonal herb Glechoma hederacea in nutritionally heterogeneous environments.

2  There were six treatments providing different degrees of patch contrast. These ranged from maximum contrast, in which patches consisted entirely of compost or sand, to homogeneity, in which all patches contained 50% of each. These were combined factorially with two patch size treatments. Overall, all treatments provided the same quantity of compost and sand, and the same area and volume of higher and lower quality patches.

3  Clones in the large-patch environments produced significantly more root biomass in both rich- and poor- quality patches than the clones in the small-patch environments. At both scales there was a decline in root biomass in the rich patches, accompanied by an increase in root biomass in the poor patches, as patch quality converged.

4  The proportion of the root biomass of clones that was located in nutrient-rich patches was greatest at high contrast and declined gradually to become equal in all patches, as contrast between patches diminished to homogeneity. This effect was independent of patch scale. There was a close match between root placement and nutrient availability in different quality patches in all treatments except that with the highest contrast.

5  At both patch scales, root : shoot ratios of clone parts in rich patches rose (and those in poor patches declined) as patch contrast increased. This species is therefore capable of morphological specialization at a local level when clones grow in heterogeneous environments. These effects were also greater at the larger patch scale.

6  The effect of patch contrast on total clone yield was significantly modified by patch scale. At lower contrast, yield was similar at both scales, whereas at higher contrast, yield was significantly greater in the large-patch treatment.

7  Although G. hederacea can match its morphology to environmental heterogeneity in some habitats, it is less able to do so when patches are small-scale and highly contrasting. These limitations cause considerable differences in the yield that can be achieved from a given quantity of resource provided in different configurations.