Print PageHigh litter biomass is hypothesized to produce an invader-directed invasion by changing ecosystem processes (e.g. nutrient cycling and light) (Ehrenfeld 2003, Farrer and Goldberg 2009). The presence of litter suppresses competition and may result in a positive feedback mechanism where the plant changes its environment in a way that benefits itself (Minchinton et al. 2006). In this study we investigated the effect of litter biomass (none, low, high) and genotype (native or invasive range, low or high C:N ratio storage) on the growth of a widespread clonal wetland invader, Phalaris arundinacea. Specifically, our objectives were to determine; 1) whether Phalaris genotypes respond equally to different levels of litter deposition and 2) the effect of litter quality and biomass on decomposition rates. Using a full-factorial design, we manipulated Phalaris litter deposition (0, 52.7, and 106.0g per ¼m2) on one-year-old tiller clones and measured differences in 16 genotypes for the following year. Concurrently, we placed litter decomposition bags of varying genotypic sources and masses to compare decomposition rates and nutrient content changes.
Results/Conclusions
Phalaris survivorship was reduced by 38% after overwintering with high litter (p=0.0071), and remained lowest under high litter deposition through the end of the experiment. Litter delayed springtime emergence by 10-11 days (p<0.0001) and the initial number of tillers in high litter treatments by 21% (p=0.0043). Phalaris shoot growth in high litter treatments occurred at a faster rate during the growing season and produced 30% taller tillers compared to low litter treatments (p=0.0101). High C:N storage genotypes also had 34% more leaves when grown in high litter. Root:shoot ratio decreased with increased litter depth (p=0.0448) after a full growing season. Mass per tiller increased 53% between high litter and no litter treatments (p=0.0161) and were 41% higher in high C:N storage genotypes. Litter decomposition rates were lowest in litter with high C:N content (p=0.0388) and 12% higher in high biomass litter bags (p=0.0156). These results indicate that during the establishment of Phalaris, litter depth negatively impacts the species initially. Tillers able to emerge through high litter are able to grow faster and with a greater investment of resources into shoots, taking advantage of elevated resources and producing the foundation for a positive feedback system encouraging its own invasion. This especially hold true for genotypes with high C:N storage (low N content), all of which were from the invasive range.
