Document: SAR-3-33-20

Seasonal differences in plant organic nitrogen uptake in a boreal peat bog.

GLASER, S.*, L.C.JOHNSON, A.W.H.DAMMAN and B.STORK

Kansas State University, Manhattan, Kansas 66506 USA ¹

Abstract:
Our studies indicate that inorganic sources of nitrogen (N) supply only 25% of N required by plants on ombrotrophic peat bogs in Maine. Our objective was to determine if ericoid mycorrhizal dwarf shrubs are capable of utilizing organic N in the field to compensate for a deficit of inorganic N. Separate plots (25 25 cm) were injected at 10 cm depth with ¹⁵N¹³C glycine (0.2 g¹⁵N/m², both carbons labeled) in August 1998. If both ¹⁵N and ¹³C are detected, then glycine was taken up intact. The common boreal shrubs, Ledum, Chamaedaphne, Gaylusaccia, and Kalmia, were harvested 2, 8, and 22 hours after injection and analyzed for ¹⁵N and ¹³C. By 22 hours later, roots were slightly enriched in ¹⁵N (175 - 350 ) but took up only 0.75% of ¹⁵N supplied. Roots showed only a 1 enrichment of ¹³C. Neither ¹⁵N nor ¹³C were detected in leaves. Results indicated minimal uptake of organic ¹⁵N in August and suggest glycine is mineralized before being accessible to plants. However, organic N uptake may differ seasonally and could be greater earlier in the season. To test this hypothesis, a similar tracer experiment was conducted in June 1999. Plots were injected with either ¹⁵N H₄ or ¹⁵N¹³C glycine and harvested 2, 8, and 22 hours and 4 days later. Preliminary results from June indicated enriched ¹⁵N in leaves. Thus, phenological differences may play a role in plant N uptake dynamics. If plants use significant amounts of organic N early in the season, this may explain how plants compensate for an insufficient supply of inorganic N.

Keywords: organic N, ericoid mycorrhizae

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.