Nutrient Sharing in Natural Clonal Fragments of Fragaria Chiloensis

Abstract

1 The potential advantages of clonal growth in plants include increased growth due to resource sharing between ramets in patchy environments. Net increases in the biomass and vegetative spread of clones attributable to resource sharing have been amply demonstrated in artificial environments, but little tested in natural ones. This study examines nutrient sharing in the stoloniferous perennial herb Fragaria chiloensis in a natural population on coastal sand dunes in California. The main questions asked were: (1) How extensive is nutrient sharing? (2) Do patterns of nutrient sharing change in response to nutrient patchiness? (3) Does nutrient sharing increase growth? 2 Three experiments were conducted, using clonal fragments in situ. Experiment 1 examined the extent of nutrient sharing when nutrient patchiness was minimal for the habitat, by tracing the movement of '5N within fragments that had all their ramets in low-nutrient microsites. Experiment 2 compared the extent of nutrient sharing when patchiness was maximal, by measuring the biomass and size of clonal fragments when a high-nutrient patch was artificially created around one of the ramets. Experiment 3 examined the effects of nutrient uptake without sharing, by measuring the growth of single ramets in high-nutrient patches. 3 Nitrogen was shared between all the ramets along a stolon, but large net transfers took place only from older to younger ramets. There was no evidence that these patterns changed in response to the degree of nutrient patchiness. Apparent effects of nutrient sharing on growth included a significant increase in the total biomass of younger ramets, a possible decrease in the biomass of some older ramets, and an increase in allocation to new stolons in ramets that imported nutrients. 4 These effects of nutrient sharing seem likely to speed the growth of fragments away from high-nutrient patches, and so, at first sight, may appear disadvantageous. However, the long term effect of accelerated spread away from good patches must be tested in relation to natural patterns of resource patch dynamics.