PARENT SESSION
Oral Session #94: Nutrient Cycling.
Presiding: R. Yanai
Thursday, August 8. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.

N- and P-limitation in an arctic salt marsh: effects on plant growth and stoichiometry.

Ngai, Jackie^*,1, Jefferies, Robert¹, ¹ University of Toronto, Toronto, Ontario, Canada

ABSTRACT- The role of nitrogen and phosphorus levels in limiting above-ground primary productivity was examined in an arctic salt marsh grazed by snow geese in order to determine (1) whether the marsh is nitrogen- or phosphorus-limited and (2) how successional age influences this limitation. Experimental plots were set up in younger and older marsh sites and fertilized with N and P in a factorial design. When either N or P was added alone, the above-ground biomass did not differ from that of the control plots. However, there were significant increases in above-ground biomass when nitrogen and phosphorus were added together, with the highest nitrogen treatment having the greatest response, irrespective of the amount of phosphorus added. In addition to above-ground biomass, tissue nutrient content was also determined for nitrogen, phosphorus and carbon for each treatment. The relative levels of these nutrients can indicate the extent to which the plants are nitrogen- or phosphorus-limited in each of the treatments. The results show that the marsh is primarily nitrogen-limited, although phosphorus rapidly becomes limiting when the nitrogen supply is supplemented. The results also indicate an interactive effect of N and P levels on plant growth and tissue nutrient status, which can be characterized as the C:N:P ratio and related to the foraging preferences of geese.

KEY WORDS: above-ground primary productivity, c:n:p ratio, nutrient limitation, site successional age