PARENT SESSION
Oral Session #68: Nutrient Cycling. Presiding: D. Johnson.
Thursday, August 9, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.

P limitation in boreal forests: effects of Al and Fe in the humus layer.

Giesler, Reiner¹, ¹

ABSTRACT- Boreal forests are generally N limited but forested groundwater discharge (DI) areas may be the exception. Here I will discuss how hydrochemistry and N availability may interrelate to P availability in DI areas. Phosphorus retention is often stratified in spodosols, the dominating soil type in Scandinavian boreal forests. Biological sinks dominate in the forest floor and geochemical sinks dominate in the mineral soil. In DI areas an upward waterflow can redistribute Al, Fe from the mineral soil into the forest floor that will generate sorption sites for both inorganic and organic P compounds. The addition of a geochemical sink in the forests floor can decrease plant P availability. Adsorbed organic P compounds may also be less susceptible to enzymatic biodegradation since the organic P compound is bound to the surface via the phosphate group and thus blocked for attack by phosphatase enzymes. This may explain the accumulation of organic P in the forest floor of DI areas. N availability in boreal forests seems to be related pH and base saturation. The combination of high N availability and the addition of a geochemical P sink in the forest floor may be the basis for a situation where P rather than N is the most limiting nutrient for forest production.

KEY WORDS: P limitation, boreal forest, P sorption, plant availabilty