P04 Nutrient dynamics along the forest floor-mineral soil continuum

Until to date, the role of the forest floor for forest nutrition is not fully understood.

Slow turnover of the forest floor (FF) is often assumed to be related to immobilisation of nutrients within the organic matter. This is in contrast to the overall hypotheses of the main project, i.e. that thick FF represents an adaptation to low nutrient supply by mineral soils. The project will investigate under which conditions slow turnover of FF material might be an advantage. The objective is to determine which processes control the relevance of the FF for tree nutrition as compared to the mineral topsoil.

For this purpose, mobilization kinetics of the macronutrients from FF and A horizons are studied performing soil dialysis and using an infinite sink approach with ion exchange resins. To study the effects of minerals in the FF on nutrient mobilization, a novel method based on litter and OF bags with admixture of the respective minerals is used. How tree species affect nutrient mobilization in the FF and in the upper mineral soil, mesocosms with labeled litter at controlled conditions of a Danish broadleaf tree species experiment are analyzed.

All in all, novel methods to study phytoavailable macronutrients in the forest soil will reveal the role of the forest floor for tree nutrition and contribute to a solid basis for sustainable forest management.

Soil dialysis probe in a stirred solution containing nutrients to test its performance