PARENT SESSION
Contributed Oral Session 32: Soil Nutrient Dynamics and Acid Deposition
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal
Nutrient resorption from senescing fine roots of four northern temperate tree species.
Kunkle, Justin *,1, Walters, Michael1, Kobe, Richard 1, 1 Department of Forestry, East Lansing, MI, USA
ABSTRACT- Nutrient resorption from senescing leaves is a well-documented nutrient conservation strategy. Fine roots may function similarly to leaves, but evidence for root resorption is equivocal. To estimate root nitrogen (N) resorption we harvested live and dead fine roots (<2 mm in diameter) from fertilized (N + calcium) and unfertilized three-year old potted seedlings of four broad-leaved tree species (Acer rubrum, Acer saccharum, Betula alleghaniensis and Populous tremuloides). Resorption was estimated by evaluating differences in N concentration per unit mass and per unit length of roots and via changes in Ca:N ratios. Because Ca is immobile, increased Ca:N ratios in dead vs. live roots indicate N resorption. We found no evidence of resorption on a root mass basis. However, we found modest root resorption when expressed on a root length basis [(mg N/cm root) (range 2-26% resorption)]. Greater Ca:N ratios in dead than live roots for all species (range 7.5-99% greater) also suggest N resorption. Other factors may affect change in nutrient contents as roots senesce (i.e. microbrial immobilization of N, leaching). Nonetheless, our results are the first, to our knowledge, to document N translocation from roots. Regardless of how it was expressed, root resorption did not vary with species or fertilizer treatments, but there was a strong positive correlation between dead and live root nitrogen concentrations for data pooled across fertilizer treatments and species (p < 0.0001; n = 8), indicating that N in live fine roots is a major determinant of senesced root N. Patterns in N content of dead fine roots and resorption have implications for whole-plant nutrient budgets and ecosystem nutrient cycling.
Key words: root resorption, fine roots, nutrient concentrations and retranslocation, Ca:N