Moss carpets constrain the fertilizing effects of herbivores on graminoid plants in arctic polygon fens

• Published in: Botany
• Main Authors: Pouliot, Rémy, Rochefort, Line, Gauthier, Gilles
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2009
• Subjects: Bylot Island
• Online Access: http://dx.doi.org/10.1139/b09-069; http://www.nrcresearchpress.com/doi/full-xml/10.1139/B09-069; http://www.nrcresearchpress.com/doi/pdf/10.1139/B09-069

We conducted a fertilization experiment in polygon fens that were grazed by Greater Snow Geese on Bylot Island (Canadian Arctic) to determine whether mosses can interfere with nutrient cycling and thereby prevent a direct fertilizing effect of herbivore faeces on vascular plants. We measured the effects of nitrogen (N), phosphorus (P), and faecal addition on growth parameters and nutrient content of graminoids and mosses over a 2 year period. Growth and nutrient content of graminoids were enhanced only for high levels of N addition (5 g·m –2 per season), and showed little response to P addition. Although the growth of mosses showed a slight response to N or P addition, it is primarily nutrient content that was generally enhanced at all levels of fertilization. In many cases, stronger responses were detected when N and P were applied in combination, rather than singly. Addition of goose droppings had no effect on any measured parameters. Our results suggest that bryophytes act as a natural barrier by absorbing nutrients from external additions, thus blocking the access of highly assimilable nutrients to graminoid plant roots. At increased levels of N addition, bryophytes were apparently saturated so the nutrient surplus leached down to roots and was thus available for graminoid plant growth. The presence of a thick moss layer likely explains why the deposition of faeces by herbivores such as geese has no effect on graminoid growth in arctic polygon fens.