PARENT SESSION
Poster Session # 14: Forest Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Carbon allocation in roots: to forage or for storage?

Iyer, Meera^*,1, Kobe, Richard¹, Walters, Michael¹, ¹ Michigan State University, East Lansing, MI

ABSTRACT- To understand the functional significance of intra- and inter-specific variation in carbon allocation to storage versus soil resource uptake, we examined total nonstructural carbohydrates (TNC) and specific root area (SRA) in the roots of seedlings of eight northern hardwood tree species. Seedlings were grown in a greenhouse under two levels of light (2% and 22% full sun) and nitrogen availability (0.5 mg/L and 50 mg/L of N in a modified Hoagland solution). These resource levels span the range of variation found in northern Michigan forests. Seedlings were harvested 12, 40, 85 and 105 days after germination. SRA (root surface area / total root mass) showed no change with nitrogen availability in most species although it increased under low light, suggesting greater foraging for nutrients under lower light. However, the usual calculation of SRA is confounded by TNC: we expect stored reserves to be less relevant to nutrient uptake than structural root mass. We therefore introduce the concept of structural specific root area (SSRA), calculated by normalizing root surface area with only root structural biomass (hence excluding TNC pools which made up 25 to 80% of root mass across species and treatments). SSRA provided a different picture of plant strategies. Species associated with low-fertility sites such as Quercus velutina and Q. alba maintained constant allocation to foraging (i.e. SSRA) across light and nutrient levels, but increased TNC under low nitrogen availability. Acer rubrum, often associated with intermediate and higher fertility sites, strongly increased SSRA under low nitrogen levels. Light-demanding Betula papyrifera maintained high SSRA across nitrogen levels and had the lowest stored reserves among the species examined. Our results demonstrate the importance of distinguishing between root biomass allocation to structural and labile carbon pools in understanding the functional significance of both root foraging and carbon storage.

Key words: biomass allocation, nonstructural carbohydrates, foraging