Growth responses of a rhizomatous herb <I>Bolboschoenus planiculmis</I> to scale and con-trast of soil nutrient heterogeneity

Abstract

Aims Spatial heterogeneity in soil nutrients is common in nature, and clonal plants are supposed to be able to better use spatially heterogeneously distributed soil nutrients. Although scale and contrast are two of the most important elements of spatial heterogeneity, few studies have tested effects of scale and contrast of soil nutrient het- erogeneity on the growth of clonal plants. Methods We conducted a greenhouse experiment in which we grew individual ramets of a rhizomatous clonal plant, Bolboschoenus planiculmis (synonym Scirpus planiculumis), in heterogeneous conditions consisting of nu- trient-rich and nutrient-poor patches. The experiment had two levels of patch scale (large vs. small patch) crossed with two levels of patch contrast (high vs. low contrast), thereby consisting of four treatments. In each treatment, the total area of the nutrient-rich patches and that of the nutrient-poor patches were the same, and the total amount of soil nutrients was also the same in all the four treatments. Important findings At both clone (whole plant) level and patch level, patch scale, contrast or their interaction did not significantly affect biomass, number of ramets, total rhizome length or number of tubers of B. planiculmis. At the patch level, however, biomass, number of ramets, total rhizome length and number of tubers of B. planiculmis were significantly greater in the nutrient-rich patches than in the nutrient-poor ones, whereas spacer length (i.e., distance between adjacent ramets) was smaller. Such effects depended on neither patch scale nor patch contrast. Therefore, when growing in environments with heterogeneous soil nutrients, B. planiculmis was able to shorten its spacer length and likely also increased branching intensity of the rhizomes, such that more ramets and tubers (i.e., potential ramets) were placed in nutrient-rich patches. These responses are generally considered one aspect of the foraging behavior of clonal plants and are thought to be adaptive. However, the patch scale or contrast designed in the present experiment could not affect the placement of the ramets in the heterogeneous environments. We presume that the responses of B. planiculmis are likely different if a wider range of scale and contrast is used and thus future studies to test effects of scale and contrast of resource heterogeneity should consider a wider range of scale and/or contrast.