Demography of fine roots in response to nutrient applications in a Norway spruce stand in southwestern Sweden

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Abstract
Effects of nitrogen and sulphur (ammonium sulphate [NS] application), nitrogen, other nutrients and water (liquid fertilization; LF), and N-free fertilizer (N-free) on fine root dynamics (production, mortality and longevity) were studied in a Norway spruce stand, using minirhizotrons. Data were collected and analysed during a two-year period at depths of 0–20 cm, 21–40 cm and 41–85 cm, five to six years after the start of fertilizer application. Ammonium sulphate application resulted in lower fine root length production at all depths compared with other treatments. Fine root length mortality in the NS treatment was higher than the control (C) and N-free fertilizer plots. Root length production in liquid fertilization was lower compared with control plots at depth 0–20 cm and higher at depth 41–85 cm compared with other treatments. N-free fertilisers lowered fine root mortality relative to control and ammonium sulphate application. N-free fertilizer extended the longevity of fine roots while ammonium sulphate application and liquid fertilization (N treatments) shortened fine root longevity. Median life span of fine roots in N-free, LF, C and NS plots was 350, 280, 280 and 250 days, respectively. It was concluded that a high input of nitrogen increased fine root mortality and decreased production and longevity whilst addition of nitrogen-free fertilizer extended fine root longevity.