Research

Plant nitrogen (N) nutrition is a topic that challenges the researcher with a number of problems not encountered in other areas of plant mineral nutrition research. The diversity of N forms present in the soil, their interconversions, their different chemical and physical characteristics and not the least the multitude of adaptations and acclimatisations that plants display to optimize acquisition of various N forms all contribute to the complexity of plant N nutrition.

Thus, plants can use a wide array of chemical N forms, ranging from the simple inorganic N compounds such as NH4+ and NO3- as well as polymeric N forms such as proteins. My research deals with plant N physiology, particularly N acquisition and metabolism of forest plants. This research spans from detailed studies of uptake processes to forest fertilization and environmental effects of N.

Left: Tests with arginine based fertilizer in a seedling nursery Rotorua, New Zeeland. Right: Selection on D-amino acids.

We have studied uptake of various N forms and demonstrated how field-grown plants acquire different organic N compounds. These studies have stimulated us to characterize the molecular mechanisms underpinning plant organic N nutrition, specifically the specific transporters mediating uptake of various amino acids as well as metabolism of absorbed organic compounds.

We have discovered that plants have a well-developed capacity for using the common L-enantiomers of amino acids but a very restricted capacity to metabolise their D-counterparts. We have also shown how transgenic plants expressing genes encoding D-amino acid metabolising enzymes can detoxify and grow on D-amino acids. This finding has formed the basis for the development of a new selectable marker in plant biotechnology, now commercialized under the tradename SELDA. Basic L-amino acids, and in particular L-arginine, are absorbed at high rates by many plants and we have shown that such N forms have specific advantages for cultivation of woody plants such as conifer seedlings.

This finding forms the basis for the development of a new fertilizer – arGrow®, which is now commercialized by the company SweTree Technologies.

Read more about Torgny Näsholm's research here

Key Publications

• Näsholm, T., Kielland, K. & Ganeteg, U. (2009). Uptake of organic nitrogen by plants. Tansley Review New Phytologist, 182: 31- 48.
• Svennerstam, H., Ganeteg, U., Bellini, C. & Näsholm, T. (2007). Comprehensive screening of Arabidopsis mutants suggests the Lysine Histidine Tranporter 1 to be involved in root uptake of amino acids. Plant Physiology 143: 1-8
• Erikson, O., Hertzberg, M. & Näsholm, T. (2004). A conditional marker gene allowing both positive and negative selection in plants. Nature Biotechnology, 22: 455-458.
• Lipson, D. and Näsholm, T. (2001). The unexpected versatility of plants: Organic Nitrogen Use and Availability in Terrestrial Ecosystems. Commissioned review. Oecologia 128: 305-316
• Näsholm, T., Ekblad, A., Nordin, A., Giesler, R., Högberg, M. and Högberg, P. (1998). Boreal forest plants take up organic nitrogen. Nature 392, 914-916, 1998.