EXPLOITATION OF PATCHILY DISTRIBUTED SOIL RESOURCES BY THE CLONAL HERB GLECHOMA-HEDERACEA

1 To allow assessment of the ability of plants to exploit heterogeneou s habitats, the growth of the stoloniferous herb Glechoma hederacea wa s compared in three artificial soil environments. In the control treat ment named 'uniform', potting compost was evenly mixed with sand; the treatment named 'patchy' contained the same quantity of potting compos t, but half was concentrated in a central resource-rich circle in each box. In the treatment named 'low', compost was distributed homogeneou sly as in the first treatment, but the total quantity of potting compo st was halved. 2 The biomass of G. hederacea produced in the patchy tr eatment was over two and a half times that produced in the uniform tre atment, and over ten times that produced in the low treatment. In addi tion, more leaves were produced in the patchy treatment than in the ot her two treatments. Almost twice as many stolons reached the perimeter s of the boxes, in the patchy treatment as in the uniform treatment. H owever, the biomass of the portions of the clones that had no basipeta l connections via stolons into the central circle did not differ betwe en treatments. 3 There was little evidence that above-ground biomass o r ramets were concentrated inside the central circle of the patchy tre atment relative to the other two treatments. 4 In contrast, 80% of the root biomass of plants in the patchy treatment was concentrated withi n the resource-rich central circle. Contrary to the situation in plant s 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 r oots 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, lo cal delay or advancement of the initiation of root growth, in response to variations in soil characteristics, could have generated the obser ved concentration of root biomass inside the central circle of the pat chy treatment. 6 G. hederacea can exploit environmental heterogeneity through local functional specialization of plant parts. In many habita ts, species that have this ability may outcompete those adapted solely to resource-poor conditions.