Document: CHR-3-33-4

Sapling stem-nitrogen dynamics in a southern New England forest.

TRIPLER, C.E.*

Idaho State University, Boise, ID 83201 USA ¹

Abstract:
Nitrogen limits growth of saplings in New England forests. However, under the low light conditions of a closed canopy forest, saplings may be unable to utilize available nitrogen during the growing season. I hypothesized that saplings take up and store nitrogen over-winter in their stems. To test this hypothesis I fertilized saplings of each of 9 dominant canopy tree species in northwestern Connecticut under gap (high-light) and closed canopy (low-light) conditions in the springs of 1997 and 1999. Saplings were harvested the following fall and processed for stem N-concentration. Species, fertilization, and light treatments were significantly different in stem-N concentration (P < 0.001, P < 0.005, P < 0.05, respectively) but higher order interactions were non-significant. Saplings did not uniformly sequester N in their terminal stems under low light conditions. For example, under fertilized low light conditions, red oak ( Quercus rubra ) stem-N concentration was 0.947% versus 1.623% for sugar maple ( Acer saccharum ) . Nor did saplings significantly increase their relative growth rate with increases in N-availability. Moreover, there was a large range of values in the N-stem concentration for each species under any set of experimental treatments. Phenology, plant architecture, and source-sink dynamics of individual species may all influence patterns of nitrogen storage. This would suggest that tree species in northeastern forests might not be hardwired to store nitrogen in similar ways. Differences in sapling stem N-concentration may explain differences in browse frequency on some species. Differences in browse frequency may alter the success of saplings and therefore, can be one factor in maintaining a diverse forest composition.

Keywords: nitrogen, saplings, Southern New England, stem-N concentrations

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