Root and shoot plasticity of the stoloniferous herb Ajuga reptans L. planted in a heterogeneous environment

In a greenhouse experiment, single ramets of Ajuga reptans, a stoloniferous herb, were planted on the divider of two halves of trays. The two halves of a tray had the same or different nutrient supply. The aim was to study root and shoot plasticity and the placement of ramets and roots in response to the heterogeneous nutrient environment. Number of primary stolons, number of secondary stolons, stolon internode length, number of leaf ramets, total root length (including fine and coarse roots) and root dry weight were greater, but biomass allocation to fine and coarse roots and specific coarse root length were lower under the homogeneous nutrient-rich (the HH-treatment) than under the homogeneous nutrient-poor (the LL-treatment) conditions. No significant response was observed in specific stolon length and specific fine root length. In the heterogeneous nutrient environment (the HL-treatment), total root length, root dry weight, root biomass allocation and specific root length did not differ between the nutrient-rich and the nutrient-poor halves of the trays for both fine and coarse roots. The same response pattern was found for the number of primary and secondary stolons, the number of leaf ramets, spacer lengths between leaf-ramets (internode length) and specific stolon length. Only the number of shoot ramets was larger in the nutrient-rich than in the nutrient-poor patch. Ajuga reptans responded strongly to the different homogeneous nutrient supplies (the HH-treatment vs. the LL-treatment) in terms of morphology and growth of roots and shoots. In the heterogeneous environment (the HL-treatment), the differences in response to local nutrient conditions seemed to be reduced due to intraclonal physiological integration. Predictions of an increase in root mass in the nutrient-rich patch as compared to root mass in the homogeneous HH-treatment or even in the nutrient-poor patch of the HL-treatment were not confirmed by the results. Apparently, behaviour of clonal plants in a heterogeneous environment cannot be simply predicted from their behaviour in different homogeneous environments.