title: Uptake of organic nitrogen by plants.
abstract: Languishing for many years in the shadow of plant inorganic nitrogen (N) nutrition research, studies of organic N uptake have attracted increased attention during the last decade. The capacity of plants to acquire organic N, demonstrated in laboratory and field settings, has thereby been well established. Even so, the ecological significance of organic N uptake for plant N nutrition is still a matter of discussion. Several lines of evidence suggest that plants growing in various ecosystems may access organic N species. Many soils display amino acid concentrations similar to, or higher than, those of inorganic N, mainly as a result of rapid hydrolysis of soil proteins. Transporters mediating amino acid uptake have been identified both in mycorrhizal fungi and in plant roots. Studies of endogenous metabolism of absorbed amino acids suggest that L- but not D-enantiomers are efficiently utilized. Dual labelled amino acids supplied to soil have provided strong evidence for plant uptake of organic N in the field but have failed to provide information on the quantitative importance of this process. Thus, direct evidence that organic N contributes significantly to plant N nutrition is still lacking. Recent progress in our understanding of the mechanisms underlying plant organic N uptake may open new avenues for the exploration of this subject.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Torgny
authors.initials: T
authors.lastname: Näsholm
authors.affiliation: Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775-0180, USA.
authors.forename: Knut
authors.initials: K
authors.lastname: Kielland
authors.affiliation: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Ulrika
authors.initials: U
authors.lastname: Ganeteg
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009930:Organic Chemicals / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D012987:Soil
chemical_list: D000596:Amino Acids; D026901:Membrane Transport Proteins; D009930:Organic Chemicals; D012987:Soil; D009584:Nitrogen