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

The successful establishment of an invasive plant species in a new environm ent depends upon the interplay between the plant's genetic diversity and mo rphological plasticity and the physical and biotic environment it encounter s. 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 soi l moisture, species composition, and vegetative cover. We found that P. aru ndinacea produced more above- and belowground biomass in sparsely vegetated plots than in densely vegetated plots, but biomass production was not affe cted by soil moisture. There was also a significant clone x vegetative cove r interaction. Genotypes differed in how strongly their growth was inhibite d by dense vegetative cover. Vegetative cover also influenced biomass alloc ation patterns. As vegetative cover increased, P. arundinacea allocated mor e biomass to roots, a strategy that gives transplants a competitive advanta ge 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, difference s among genotypes in their response to vegetative cover suggest that contin ual introductions of new genotypes of reed canary grass substantially incre ase the chance that a particular genotype will flourish and spread.