title: The below-ground perspective of forest plants: soil provides mainly organic nitrogen for plants and mycorrhizal fungi.
abstract: • Nitrogen (N) availability has a major impact on a wide range of biogeochemical processes in terrestrial ecosystems. Changes in N availability modify the capacity of plants to sequester carbon (C), but despite the crucial importance for our understanding of terrestrial ecosystems, the relative contribution of different N forms to plant N nutrition in the field is not known. Until now, reliably assessing the highly dynamic pool of plant-available N in soil microsites was virtually impossible, because of the lack of adequate sampling techniques. • For the first time we have applied a novel microdialysis technique for disturbance-free monitoring of diffusive fluxes of inorganic and organic N in 15 contrasting boreal forest soils in situ. • We found that amino acids accounted for 80% of the soil N supply, while ammonium and nitrate contributed only 10% each. In contrast to common soil extractions, microdialysis revealed that the majority of amino acids are available for plant and mycorrhizal uptake. • Our results suggest that the N supply of boreal forest soils is dominated by organic N as a major component of plant-available N and thus as a regulator of growth and C sequestration.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Erich
authors.initials: E
authors.lastname: Inselsbacher
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.|Department of Forest Genetics and Plant Physiology, Umeå Plant Science Center, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Torgny
authors.initials: T
authors.lastname: Näsholm
mesh_terms: D004058:Diffusion; D017551:Microdialysis; D038821:Mycorrhizae / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D014197:Trees / Q000378:metabolism* / Q000382:microbiology*
chemical_list: D012987:Soil; D009584:Nitrogen