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1 Nutrient-rich patches can occur in soils at a wide range of spatial and temporal scales. Differences in the root proliferation response between species may be due to differing abilities of root systems to locate and recognize patches of differing size and nutrient concentration. 2 We investigated the root proliferation responses of seven co-occurring herbaceous perennial British woodland species (Ajuga reptans, Glechoma hederacea, Oxalis acetosella, Silene dioica, Stachys sylvatica, Veronica montana and Viola riviniana) and the effect of mycorrhizal colonization on any response. 3 Plants were planted in nutrient-poor sand in the centre of rectangular pots, with a nutrient-rich patch to one side and a control (sand) patch on the other. Size and nutrient concentration of the patches were varied between treatments. 4 Species differed in the size of their root systems and in their ability to respond to localized nutrient-rich patches. Oxalis acetosella and Viola riviniana, which produced the smallest root systems, showed similar root growth in nutrient-rich and control patches. All other species responded to the presence of a nutrient-rich patch by various combinations of root proliferation, changes in root branching pattern and by an increase in specific root length. 5 In some species the response was affected by patch attributes: Silene dioica and Veronica montana were sensitive to the nutrient concentration of the patch, and Glechoma hederacea did not respond to the smallest sized patch. 6 Mycorrhizal colonization had little effect on root proliferation. Only one species (Oxalis acetosella) could be shown to benefit from colonization by increased phosphate uptake. 7 The soil is a heterogeneous environment in terms of nutrient availability; differences between species in the ability to exploit this heterogeneity may affect their distribution, and could be a mechanism that reduces interspecific root competition. Key-words: arbuscular mycorrhizal fungi, plasticity, root architecture, roots, soil heterogeneity Journal of Ecology (1999) 87, 849-859

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. Key-words: clonal plants, foraging, morphological plasticity, patch selection, root: shoot ratio Journal of Ecology (1999) 87, 860-872

1 We investigated the fine-scale below-ground distribution of plant parts in a mountain grassland. Roots and rhizomes were identified to the species level by tracking their connections to above-ground parts. 2 Fine-scale horizontal heterogeneity of total root and rhizome biomass at different depths was recorded at the same time in the same grassland. 3 Both pairwise and multivariate statistical analysis showed that in the 0-3 cm layer the frequencies of roots and rhizomes of individual plants were closely coupled to the occurrence of the same species immediately above-ground. In contrast, in the 3-6 cm layer, these correlations peaked when root and rhizome frequencies were compared with plants above-ground displaced by a horizontal distance of 2 cm. This confirms the predominantly inclined growth of both roots and rhizomes; while the inclined growth has been shown regularly by studying single plants, the current study shows its prevalence at the community level as well. 4 The similarity to the above-ground patterns in the upper soil layer was due to the spatial constraints of plant presence above-ground: in contrast, the spatial patterns in the 3-6 cm layer were independent of plant presence above-ground. The role of root growth plasticity is discussed in this context. 5 Autocorrelation analysis of the root data revealed that there was a pronounced difference in the grain of horizontal spatial pattern between total root biomass and species-specific root frequencies. All the species had rather loose root systems and clumps of one species rarely extended more than 0.5 cm. In contrast, there was significant long-range clumping of root biomass up to 10 cm. The below-ground heterogeneities in overall biomass and in species-specific distributions were therefore probably determined by different environmental processes. 6 No such difference in clumping range between total biomass and species-specific frequencies was observed in above-ground parts. This was attributed to homogeneity of the above-ground resource (light) compared with the inherently heterogeneous nature of the below-ground resources, and the different nature of competition for these resources may account for differences in vegetation patterns above- and below-ground. Keywords: fine-scale, horizontal heterogeneity, multivariate analysis, rhizomes, roots, vertical distribution