Effects of ammonium and aluminium on the development and nutrition of Pinus nigra in hydroculture.

Application of ammonium and aluminium to young Pinus nigra var. maritima (Ait.) Melville trees resulted in a variety of negative effects. Excess ammonium led to an increase in shoot/root ratio. The biomass of the fine roots declined, resulting in an increase of the coarse/fine root ratio. The degree of mycorrhizal infection of the roots decreased. The nitrogen content of the trees increased considerably, whereas particularly the levels of calcium magnesium, manganese and zinc decreased sharply. Excess aluminium resulted in a simultaneous reduction of root and shoot biomass, a decline of the fine root system, an increase in the coarse/fine root ratio and a decrease in the degree of mycorrhizal infection. Uptake of the divalent cations calcium, magnesium, iron, manganese and zinc was restricted substantially, The nitrogen and phosphorus contents of the trees were hardly affected, whilst the potassium content of the shoot increased and of the roots decreased. This implicates that a deteriorating fine root system has to supply water and nutrients to a more demanding shoot. In the long term, high ammonium inputs and aluminium dissolution in forest ecosystems will lead to substantial nutrient deficiencies, just as has been found in the field.