title: Ectomycorrhizal impacts on plant nitrogen nutrition: emerging isotopic patterns, latitudinal variation and hidden mechanisms.
abstract: Ectomycorrhizal (EcM)-mediated nitrogen (N) acquisition is one main strategy used by terrestrial plants to facilitate growth. Measurements of natural abundance nitrogen isotope ratios (denoted as δ(15)N relative to a standard) increasingly serve as integrative proxies for mycorrhiza-mediated N acquisition due to biological fractionation processes that alter (15)N:(14)N ratios. Current understanding of these processes is based on studies from high-latitude ecosystems where plant productivity is largely limited by N availability. Much less is known about the cause and utility of ecosystem δ(15)N patterns in the tropics. Using structural equation models, model selection and isotope mass balance we assessed relationships among co-occurring soil, mycorrhizal plants and fungal N pools measured from 40 high- and 9 low-latitude ecosystems. At low latitudes (15)N-enrichment caused ecosystem components to significantly deviate from those in higher latitudes. Collectively, δ(15)N patterns suggested reduced N-dependency and unique sources of EcM (15)N-enrichment under conditions of high N availability typical of the tropics. Understanding the role of mycorrhizae in global N cycles will require reevaluation of high-latitude perspectives on fractionation sources that structure ecosystem δ(15)N patterns, as well as better integration of EcM function with biogeochemical theories pertaining to climate-nutrient cycling relationships.
authors.affiliation: Smithsonian Tropical Research Institute, P.O. Box 0843-03092, Balboa, Ancon, Republic of Panama.
authors.forename: Jordan
authors.initials: J
authors.lastname: Mayor
authors.forename: Mohammad
authors.initials: M
authors.lastname: Bahram
authors.forename: Terry
authors.initials: T
authors.lastname: Henkel
authors.forename: Franz
authors.initials: F
authors.lastname: Buegger
authors.forename: Karin
authors.initials: K
authors.lastname: Pritsch
authors.forename: Leho
authors.initials: L
authors.lastname: Tedersoo
mesh_terms: D002980:Climate; D017753:Ecosystem; D015233:Models, Statistical; D038821:Mycorrhizae / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes / Q000032:analysis; D010944:Plants / Q000378:metabolism*; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen
keywords: 15N; Above- and below-ground interactions; nutrient cycling; nutrient limitation; plant-soil interactions; structural equation modelling; tropical ecology