Time change of aluminium toxicity in the acid bulk soil and the rhizosphere in Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) stands

Context

In acidic forest soils, aluminium can alter tree health due to its potential toxicity. Aluminium phytotoxicity is mainly influenced by its chemical form and its availability.

Methods

As physical-chemical indicators of Al toxicity in soil, Al speciation in soil solutions and in the exchange complex was measured in the rhizosphere and the bulk soil of two tree species (Norway spruce (Picea abies (L.) Karst.) and European Beech (Fagus sylvatica L.) in an acidic soil and in 4 months (November, February, May and August) representing the four seasons in a year.

Results

In the bulk soil, Al toxicity was generally higher under Norway spruce than under beech. Furthermore, temporal changes in Al behaviour were identified under Norway spruce but not under beech. The monomeric Al in the soil solutions and the exchangeable Al in the solid soil increased significantly in February under Norway spruce and were positively correlated with nitrate concentration, suggesting that nitrate influence Al speciation and mobility under Norway spruce. In the rhizosphere, Al toxicity was restricted through Al complexation by organic compounds and by nutrient contents independently from the season. The ecological importance of the rhizosphere in Al detoxification is discussed.

Conclusions

This study suggests that plant specific differences as well as seasonal changes in plant physiology, microbial activity and microclimatology influence aluminum toxicity in acid forest soils.