Acid deposition, summer drought and enhanced production of nitrate in forest soils; risk cofactors relative to forest decline. an additional hypothesis concerning the synergistical effects: The nitrous acid hypothesis

Abstract

The author suggests a new hypothesis on a triggering effect of drought on the decline of forests submitted to acid precipitation. The phase of soil drying produces a flush of decomposition of organic matter, favoured by Al³⁺, increasing the amount of C and N available for a subsequent nitrification. The first rainfall after a summer drought (FRAD) induces a surge of activity of autotrophic nitrifiers having survived the drying phase. During acidification pushes an U₂ stress resulting from rapid O₂ consumming nitrification would induce a temporal shift of NH₄ ⁺ and NO₂ oxidation giving within a few days a transient peak of HNO₂ accumulation injurious to fine roots and mycorrhizae.