Tannins, Proteins, and Soil N in the Boreal Kalmia-Black Spruce System.

The role leaf litter tannins play in controlling soil N cycling was first inferred half a century ago.  Since then, numerous studies have produced data supporting ecological succession models whereby plant communities converge towards tannin-rich conditions with soil N retained in organic forms. This presentation will outline a series of experiments whereby indirect evidence for such an autogenic successional pathway has been applied to explain the growth-check of Black Spruce (Picea mariana (Mill.) BSP) seedlings in the presence of Sheep Laurel (Kalmia angustifolia L.). More recently, Joanisse et al. provided compelling evidence based on the chemistry and protein binding capacity of litter tannins, on soil enzyme inhibition, and on the uptake of N from tannin-protein precipitates by ericoid mycorrhizas, which supports the notion that litter tannin production is an important trait in Kalmia driving ecosystem structure and processes. Future research should test the relative importance of this “pedocentric” view of ecological succession against alternative “phytocentric views”, such as the ability of Kalmia to produce allelopathic chemicals or to induce non-nutritional water stress.