Fine-root response to nitrogen supply in nitrogen manipulated Norway spruce catchment areas

Abstract

Investigations were carried out in order to assess the effect of decreased/increased nitrogen (N)- and sulphur (S)-deposition on the growth and vitality if fine-roots of Norway spruce ( Picea abies (L.) Karst.), in three catchment areas within the Lake Gårdsjön basin, SW Sweden. The catchment areas were subjected to decreased N- and S-deposition (G1 ROOF), increased N-deposition (G2 NITREX) and ambient levels of N- and S-deposition (F1 CONTROL). The excavated fine-roots (<1 mm in diameter) were separated into live and dead fractions and chemical analyses were carried out. The proportion of nitrogen to other macro-nutrients in the fine-roots was used as an indicator of mineral nutrient requirements of the forest trees. The most ‘vital’ fine-roots (characterised by high live to dead ratio) were found in all catchment areas in the upper parts of the organic soil horizon, which most frequently exhibited good mineral nutrient and soil water conditions. It was concluded from available climatic data on monthly precipitation and air temperature that the variation in fine-root growth was not caused by climatic changes. The live to dead ratio of the fine-roots gradually decreased with depth and was low in the mineral soil horizon. An increased percentage of living fine-roots in the ROOF catchment suggests an increased ‘vitality’ in fine-roots (increased live to dead ratios), associated with reduced N- and S-deposition. Chemical analyses of live fine-roots in the same area revealed improved mineral nutrient concentrations, e.g. higher Ca/Al ratios, increased concentrations of K, P, Ca and Mg. Fine-root vitality was improved in the NITREX catchment area, probably as a result of an increased cation release. Fine-root distributions, live to dead ratios and mineral nutrient concentrations appear to be strongly affected by N availability in the soil. Increased concentrations of K and P in proportion to N in fine-roots in the ROOF catchment indicate improved mineral nutrient conditions and lower risk of ion-imbalances. The results are in agreement with findings from other investigations suggesting those nutrient deficiencies and/or metal toxicity may strongly affect the growth of fine-roots.