| Abstract: | Minirhizotrons with high resolution were used to investigate how the fine-root turnover rate is influenced by extra nitrogen input to a Norway spruce stand. The stand was subjected to repeated application of ammonium sulphate (NS) and nitrogen-free fertilizers (V), the latter containing macro and micro nutrients other than nitrogen. Data were collected and analysed 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 treatments. However, the total production in the NS and V treated plots was not significantly higher than in the C plots. The annual net production (production minus mortality) was higher in NS than V plots, while 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 than the C plots during the period of study. Winter root-mortality was higher in the V plots than in the C and NS plots. No root-length mortality occurred from June to August in the V plots, while root-length mortality in the C and NS plots during this period was 56% and 55% of annual root mortality, respectively. The NS application increased the production of white roots while the V treatment decreased the mortality of white roots. The mortality of white roots during August 1991 to August 1992 in the V plots was only 8% of total fine root mortality compared with 30% in the C and 60% in the NS plots. The NS and V applications resulted in a larger root diameter than in the C plots. |
