The ''red'' decline of Norway spruce or ''røde rødgraner'' - is it ammonium overload or top-dying?

In 1989 a new disease “røde rødgraner” or “red” decline of Norway spruce (Picea abies) became a serious problem in plantations in Jutland on poor, sandy soils. Some trees became red and lost their needles over a few years. The reddening started from theshoot tips. The only important pollutant in mainly rural Jutland is ammonia from the many farms, resulting in N depositions of 10-30 kg ha-1 year-1. The ammonium hypothesis of Nihlgård (1985) stipulates that certain types of forest decline is caused byan overload of ammonia from the air. Hence the possibility that “røde rødgraner” was caused by nitrogen overload was investigated. A sensitive biochemical indicator of nitrogen status of conifer trees is the content of free amino acids of the urea cycle,arginine and ornithine. In pot experiments with four times overload of N as ammonium nitrate the free arginine content increased more than 100 times, up to almost 2 % of the fresh weight. Also trees suffering from phosphorus or potassium deficiency showedlarge increases in arginine. Needle samples from “røde rødgraner” (taken from the 6th. whorl at minimum metabolism in December) showed normal arginine and ornithine contents. There was no indication of nitrogen overload. The “red” Norway spruce maysuffer from “top-dying” a common disorder of Norway spruce in Great Britain, believed to be caused by several mild winters in a row. In that case the symptoms should diminish after the very cold winter 1995-96.