Effects of excessive ammonium deposition on the nutritional status and condition of pine needles

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Abstract
In the southeastern part of the Netherlands many Scots pine (Pinus sylvestris L.) trees show signs of yellowing. To investigate whether there is a relation between this phenomenon and the high ammonium deposition, needle and soil samples were analyzed. Soil samples from the discoloured forests contained more extractable nitrogen than samples from healthy stands, whereas differences in pH values were small. Needles from yellow trees had higher levels of total nitrogen than needles from green trees as well as severe imbalances of Mg, K+ and P relative to N. The amount of leaf pigments was substantially lower in needles of the diseased trees, but they contained much higher quantities of free arginine, which accounted for a major part of total nitrogen. This may be an indication of a severe nitrogen overload. The linkage between this excessive nitrogen nutrition and the observed process of yellowing is discussed.