Variation in the chemical quality of woody supplements for nursery growing media affects growth of tree seedlings

Abstract

Tree seedlings are produced in tree nurseries. However, nursery-grown seedlings often exhibit poor performance after outplanting due to the lack of adaptation to harsh natural conditions. These nursery-grown seedlings do not necessarily possess well-developed ectomycorrhizal symbionts, which help to obtain nutrients and increase resilience in exchange for seedling photoassimilated carbon. To improve the quality of the seedlings in natural conditions, we sowed spruce seeds on growing media with the addition of wood chips, i.e. stemwood chips or polyphenol- and resin acid-rich knotwood chips. Wood chips were chosen because they are common forest side-streams, and their compounds have shown a potential to improve mycorrhization and seedling fitness. Wood chips initially decreased the growth of seedlings. However, this effect levelled off with time and depended on the quality of the wood. Wood chips had no effect on mycorrhization. Further testing of the wood material showed that wood chips seemed to decrease seedling growth via nitrogen (N) immobilisation rather than a direct toxic effect. The phenomenon of N immobilisation on wood chips could be explored further to develop a slow-release N source, aptly reflecting N availability in natural conditions. Slow-release N source based on wood chips could be beneficial both to increase survival in natural conditions and for environment protection.