Epsilon Open Archive

Abstract

The main objectives of the work presented in this thesis were to increase our understanding of how different chemical forms of nitrogen (N) affect the growth and biomass distribution of conifer seedlings and hence their establishment and performance in field. Growth studies of Scots pine (Pinus sylvestris (L.)), Norway spruce (Picea abies (L.) Karst.) and the model plant Arabidopsis (Arabidopsis thaliana, ecotype Col-0) showed that plants can grow at similar (or higher) rates on organic N sources to those on the inorganic N sources ammonium (NH4+) and nitrate (NO3-). Cultivation on arginine also improved the field performance of Norway spruce seedlings by increasing their current-year shoot growth, despite smaller initial shoot length. Moreover, plants supplied with organic N distributed a relatively larger proportion of their biomass to root structures than controls with similar total biomass and N contents grown on inorganic N sources. Detailed studies on Arabidopsis revealed that an increase in the root:shoot ratio coincided with high retention of organic N in the roots, implying that the site of assimilation may be of importance for the short-term distribution of biomass. Further, studies on Scots pine seedlings deprived of carbohydrates suggested that the uptake, reduction and assimilation of NO3- are highly dependent on recent photoassimilates and that use of organic N may have considerable energetic benefits for plants, especially under conditions that limit carbohydrate supplies.

The results from the studies underlying this thesis highlight the potential role of organic N in the nutrition of conifer seedlings, the links between seedling nutrition, morphology and field performance, and effects of organic N on biomass distribution. They suggest that organic N may serve as an alternative or complement to inorganic N sources in seedling production, and may help attempts to improve seedling establishment in the field.