PHYSIOLOGICAL INTEGRATION OF THE CLONAL PLANT CAREX ARENARIA AND ITS RESPONSE TO SOIL-BORNE PATHOGENS

We test the hypothesis that the expansive horizontal clonal growth of Carex arenaria may provide a method of escape from soil-borne pathogen s (fungi and nematodes) by growing away from the site of infection. Pl ants were grown in non-sterilized or sterilized dune sand, i.e., with or without soil-borne pathogens. The effects of soil-borne pathogens w ere studied on the whole genet, on the mother alone, and on the first primary rhizome. Genets with the mother plant infected produced less t otal biomass and had less biomass allocated to roots than genets with uninfected mothers. Infected genets had fewer primary rhizomes and low er total rhizome length, but rhizome specific weight or the distance b etween shoots did not decrease in infected plants. In C. arenaria, uni nfected mothers with an infected first primary rhizome produced shorte r and fewer rhizomes than uninfected genets. The infected first rhizom e continued to grow at the same speed as uninfected rhizomes, probably by support from the uninfected mother plant. However, secondary rhizo me branching was affected only by direct exposure to soil pathogens an d not by the status of the mother plant. The results provide evidence that clonal growth may facilitate escape from soil-borne pathogens. Th e rhizome explores a patchy environment by supporting the growth of yo ung tillers when passing pathogenic patches.