Exceedance of critical limits and their impact on tree nutrition

Braunschweig

2013

S. 125-140

Artikel aus einer ZeitschriftUnselbständiges Werk

200179342

The atmospheric deposition of sulphur (S) and nitrogen (N) compounds affects forest ecosystems through several processes. For N limited stands, enhanced N supply may stimu-late the production of above-ground biomass. However, in excess, N loads may lead to nutri-ent imbalances and sensitivity to frost, insects, and fungi may increase (N saturation hypothe-sis, postulated by Aber et al., 1989). When N availability exceeds the capacity of the ecosys-tem to retain N, nitrate leaching from the rooting zone is enhanced. The release of acid anions such as nitrate (NO3-) and sulphate (SO4--), balanced by base cation leaching, may contribute to the acifification of soils and surface waters (acidifcation hypothesis, postulated by Aber et al., 1989). In acid soils, aluminium (Al) can be mobilized from the soil complex and have adverse effects on fine roots. Both, loss of base cations and the toxic effect of aluminium may further contribute to an unbalanced mineral nutrition of the trees.