A STUDY ON FINE-ROOT DYNAMICS IN RESPONSE TO NUTRIENT APPLICATIONS INA NORWAY SPRUCE STAND USING THE MINIRHIZOTRON TECHNIQUE

Minirhizotrons with high resolution were used to investigate how the f ine-root turnover rate is influenced by extra nitrogen input to a Norw ay spruce stand. The stand was subjected to repeated application of am monium sulphate (NS) and nitrogen-free fertilizers (V), the latter con taining macro and micro nutrients other than nitrogen. Data were colle cted and analyzed during a one-year period, 3,4 years after the start of fertilizer additions. A significant interaction of data x treatment (P<0.001) in root-length production and mortality was found between t reatments. However, the total production in the NS and V treated plots was not significantly higher than in the C plots. The annual net prod uction (production minus mortality) was higher in NS than V plots, whi le net production in the V plots was lower than in the C plots. The NS and V treatments resulted in a higher total root-length mortality tha n the C plots during the period of study. Winter root-length mortality occurred from June to August in the V plots, while root-length mortal ity occurred from June to August in the V plots, while root-length mor tality in the C and NS plots during this period was 56% and 55% of ann ual root mortality, respectively. The NS application increased the pro duction of white roots while the V treatment decreased the mortality o f white roots. The mortality of white roots during August 1991 to Augu st 1992 in the V plot was only 8% of total fine-roots mortality compar ed with 30% in the C and 60% in the NS plots. The NS and V application s resulted in a larger root diameter than in the C plots.