The effect of environmental heterogeneity on clonal behaviour of Prunella vulgaris L

We studied the response of a clonal herb, Prunella vulgaris, to its position in a gap, the identity of neighbouring graminoid species, and simulation of competition for light. The growth characteristics, such as stolon length, internode length and number of stolons were recorded in competitive environments with graminoid bunches of Molinia caerulea, Juncus effusus and Nardus stricta and in different types of gaps in a manipulative field experiment. Two pot experiments studied the effect of reduced light and of low red/far red ratio (R/FR) on the plant growth characteristics. In both field and pot experiments we monitored stolon orientation in a treatment divided into two parts (competition/shaded or gap/unshaded). Methods of circular statistics were used to evaluate stolon orientation. The graminoid bunches had equivalent effects on plant vegetative growth - plants had longer stolons and internodes than plants growing in gaps. The effects of treatments on other characteristics (amounts of stolons and leaves) were not significant. In divided treatment, plants responded by accumulation of stolons and leaves in vegetation removed part, and avoided the vegetated part. In the pot experiments the plant biomass and stolon number decreased in low R/FR and in low irradiance treatments, but the internodes in low R/FR were 26% longer compared to the control. Centroids were uniformly distributed in divided low R/FR treatment contrary to low irradiance treatment where they showed preference for unshaded part. No dependency of stolon length on its orientation was found in divided treatments of both experiments. Prunella vulgaris in heterogeneous environment distinguished favourable and less favourable conditions and produced more stolons with shorter internodes under favourable conditions. This resulted in concentration of resource acquiring structures in favourable patches.