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 pathogens (fungi and nematodes) by growing away from the site of infection. Plants were grown in non-sterilized or sterilized dune sand, i.e., with or without soil-borne pathogens. The effects of soil-borne pathogens were studied on the whole genet, on the mother alone, and on the first primary rhizome. Genets with the mother plant infected produced less total biomass and had less biomass allocated to roots than genets with uninfected mothers. Infected genets had fewer primary rhizomes and lower total rhizome length, but rhizome specific weight or the distance between shoots did not decrease in infected plants. In C. arenaria, uninfected mothers with an infected first primary rhizome produced shorter and fewer rhizomes than uninfected genets. The infected first rhizome continued to grow at the same speed as uninfected rhizomes, probably by support from the uninfected mother plant. However, secondary rhizome branching was affected only by direct exposure to soil pathogens and not by the status of the mother plant. The results provide evidence that clonal growth may facilitate escape from soil-borne pathogens. The rhizome explores a patchy environment by supporting the growth of young tillers when passing pathogenic patches.