Norway spruce fine root dynamics and carbon input into soil in relation to environmental factors

Abstract

Knowledge of the quantity of belowground litter carbon (C) input is scarce but highly valued in C budget calculations. Specifically, the turnover rate of fine roots is considered as one of the most important parameters in the estimation of changes in soil C stock. In this thesis Norway spruce (Picea abies L. (Karst.)) fine root lifespan and litter production were studied and their responses to nutrient availability and temperature were examined. Aboveground foliage and understory litter C inputs were also quantified. Furthermore, fine root isotopic C ages were compared to fine root lifespans. Increased nutrient availability and higher temperature shortened spruce fine root lifespan both in the manipulation treatments and along a latitude gradient. Fertilization improved tree growth and the absolute amount of litter production, both belowand aboveground. Soil warming, by contrast, increased the belowground litter production in relation to aboveground foliage litterfall but did not lead to long-term increases in aboveground tree growth. In warmed soil, the changes in spruce short root morphology indicated nutrient deficiency. The results indicated that in nutrient limited forests climate warming is unlikely to increase the aboveground tree growth in the long-term. Fine root litter C input into the soil in relation to the aboveground litter C input was higher towards lower fertility, due particularly to the greater contribution of understory vegetation. The structural 14 C age of fine roots was consistently 3 6 years older than fine root lifespan determined with the minirhizotron method indicating that root growth may use also use stored or recycled C. In almost all stands, fine root litter C input into the soil at least equalled the aboveground input, which confirms the significance of belowground litter production in the boreal forest C cycle. The importance of understory vegetation was also significant. In addition on understory vegetation, different stand age and tree species, more studies should also focus on the shift in the litter production pattern from aboveto belowground along environmental change as this may have an impact on litter C quality and soil C storage in boreal forest soils.