Exploitation of Patchily Distributed Soil Resources by the Clonal Herb Glechoma Hederacea

Abstract

1 To allow assessment of the ability of plants to exploit heterogeneous habitats, the growth of the stoloniferous herb Glechoma hederacea was compared in three artificial soil environments. In the control treatment named 'uniform', potting compost was evenly mixed with sand; the treatment named 'patchy' contained the same quantity of potting compost, but half was concentrated in a central resource-rich circle in each box. In the treatment named 'low', compost was distributed homogeneously as in the first treatment, but the total quantity of potting compost was halved. 2 The biomass of G. hederacea produced in the patchy treatment was over two and a half times that produced in the uniform treatment, and over ten times that produced in the low treatment. In addition, more leaves were produced in the patchy treatment than in the other two treatments. Almost twice as many stolons reached the perimeters of the boxes. in the patchy treatment as in the uniform treatment. However, the biomass of the portions of the clones that had no basipetal connections via stolons into the central circle did not differ between treatments. 3 There was little evidence that above-ground biomass or ramets were concentrated inside the central circle of the patchy treatment relative to the other two treatments. 4 In contrast, 80% of the root biomass of plants in the patchy treatment was concentrated within the resource-rich central circle. Contrary to the situation in plants grown in homogeneous conditions, root:shoot ratio was highest where soil-derived resources were locally most abundant. Inside the central circle, ramets developed roots earlier in the patchy treatment than in the uniform treatment; outside the central circle, ramets developed roots later in the patchy treatment than in the uniform treatment. 5 In a supplementary experiment the length of young root systems increased exponentially from whatever time their growth was initiated. Thus, local delay or advancement of the initiation of root growth, in response to variations in soil characteristics, could have generated the observed concentration of root biomass inside the central circle of the patchy treatment. 6 G. hederacea can exploit environmental heterogeneity through local functional specialization of plant parts. In many habitats, species that have this ability may outcompete those adapted solely to resource-poor conditions.