EFFECTS OF NUTRITIONAL-STATUS ON THE DROUGHT RESISTANCE IN NORWAY SPRUCE

Many studies have dealt with the links between nutrient supply and tre e growth. High N availability usually leads to increased growth but it may also be a stress factor and may affect the ability of the tree to take up both water and nutrients. We measured the nutritional status of the trees and estimated their tolerance to drought by examining the flushing of new shoots and needle loss. The studies were carried out on trees grown under different N and water supply in a field experimen t using a 25-30 year old Norway spruce (Picea abies) in SW Sweden. The treatments included in this study were ammonium sulphate (NS) where 1 00 kg N ha(-1) was applied yearly, N-free fertiliser (V) where P, K, C a, Mg and S but no N was applied, and also the combinations of ammoniu m sulphate and drought (ND) and N-free fertiliser and drought (VD). Th e NS treatment caused increased N but decreasing P/N, K/N and Mg/M rat ios in the needles whereas the N-free fertiliser resulted in increased PIN and Ca/N ratios. In ND and VD, nutrient ratios remained relativel y unchanged compared with NS and V. Thus, trees keep a stable internal nutrient balance. However, as a response to the drought, ND seemed to stop the flushing of new shoots to a higher degree than VD. In conclu sion, this study showed that nutrient status did affect drought resist ance which could be seen as differences in the flushing of new shoots rather than changes in nutrient ratios in the needles.