Effects of Spatial Patch Arrangement and Scale of Covarying Resources on Growth and Intraspecific Competition of a Clonal Plant

Abstract

Spatial heterogeneity in two co-variable resources such as light and water availability is common and can affect the growth of clonal plants. Several studies have tested effects of spatial heterogeneity in the supply of a single resource on competitive interactions of plants, but none has examined those of heterogeneous distribution of two co-variable resources. In a greenhouse experiment, we grew one (without intraspecific competition) or nine isolated ramets (with competition) of a rhizomatous herb Iris japonica under a homogeneous environment and four heterogeneous environments differing in patch arrangement (reciprocal and parallel patchiness of light and soil water) and patch scale (large and small patches of light and water). Intraspecific competition significantly decreased the growth of I. japonica, but at the whole container level there were no significant interaction effects of competition by spatial heterogeneity or significant effect of heterogeneity on competitive intensity. Irrespective of competition, the growth of I. japonica in the high and the low water patches did not differ significantly in the homogeneous treatments, but it was significantly larger in the high than in the low water patches in the heterogeneous treatments with large patches. For the heterogeneous treatments with small patches, the growth of I. japonica was significantly larger in the high than in the low water patches in the presence of competition, but such an effect was not significant in the absence of competition. Furthermore, patch arrangement and patch scale significantly affected competitive intensity at the patch level. Therefore, spatial heterogeneity in light and water supply can alter intraspecific competition at the patch level and such effects depend on patch arrangement and patch scale.

Keywords: Iris japonica; clonal growth; intraspecific interactions; pararell patchiness; patch scale; reciprocal patchiness.

FIGURE 1

Experimental design. The experiment had two competition treatments (without vs. with competition by growing one or nine ramets of Iris japonica in a container) crossed with five heterogeneity treatments, i.e., (i) homogeneous (all patches received moderate light and moderate water), (ii) parallel large patch (the container was divided into two large patches; one received high light and high water, and the other low light and low water), (iii) reciprocal large patch (the whole container was divided into two large patches; one patch received high light and low water, and the other low light and high water), (iv) parallel small patch (the container was divided into four small patches; two received high light and high water, and the other low light and low water) and (V) reciprocal small patch (the container was divided into four small patches; two received high light and low water, and the other low light and high water). The light and water content received by the plants in the heterogeneous treatments was the same as that in the homogeneous treatment.

FIGURE 2

Biomass (A), number of ramets (B), and rhizome length (C) of I. Japonica at the whole container level under the ten treatments. Error bars show +SE.

FIGURE 3

Completive intensity as measured by log response ratio (LnRR) of biomass of I. japonica at the whole container level (A) and in the high and low water patches at the patch level (B) in the five treatments. Error bars show +SE.

FIGURE 4

Biomass (A,D), number of ramets (B,E) and rhizome length of (C,F)I. japonica in the high and low water patches under the ten treatments. Error bars show +SE.