Effects of genotypes, soil moisture, and competition on the growth of an invasive grass, Phalaris arundinacea (reed canary grass)

Abstract

The successful establishment of an invasive plant species in a new environment depends upon the interplay between the plant's genetic diversity and morphological plasticity and the physical and biotic environment it encounters. To determine the relative importance of these factors in influencing the spread of the invasive grass, Phalaris arundinacea L. (reed canary grass), we transplanted three genotypes into a pasture that contained variable soil moisture, species composition, and vegetative cover. We found that P. arundinacea produced more above- and below-ground biomass in sparsely vegetated plots than in densely vegetated plots, but biomass production was not affected by soil moisture. There was also a significant clone beta vegetative cover interaction. Genotypes differed in how strongly their growth was inhibited by dense vegetative cover. Vegetative cover also influenced biomass allocation patterns. As vegetative cover increased, P. arundinacea allocated more biomass to roots, a strategy that gives transplants a competitive advantage during the following spring. Our results suggest that, because it grows poorly in high vegetative cover, P. arundinacea is most likely to become a pest in disturbed or low-density plant communities. Furthermore, differences among genotypes in their response to vegetative cover suggest that continual introductions of new genotypes of reed canary grass substantially increase the chance that a particular genotype will flourish and spread.Key words: biomass allocation, competition, invasive species, morphological plasticity, plant invasions, Phalaris arundinacea, reed canary grass.