title: Ectomycorrhizal Fungal Protein Degradation Ability Predicted by Soil Organic Nitrogen Availability.
abstract: In temperate and boreal forest ecosystems, nitrogen (N) limitation of tree metabolism is alleviated by ectomycorrhizal (ECM) fungi. As forest soils age, the primary source of N in soil switches from inorganic (NH4 (+) and NO3 (-)) to organic (mostly proteins). It has been hypothesized that ECM fungi adapt to the most common N source in their environment, which implies that fungi growing in older forests would have greater protein degradation abilities. Moreover, recent results for a model ECM fungal species suggest that organic N uptake requires a glucose supply. To test the generality of these hypotheses, we screened 55 strains of 13 Suillus species with different ecological preferences for their in vitro protein degradation abilities. Suillus species preferentially occurring in mature forests, where soil contains more organic matter, had significantly higher protease activity than those from young forests with low-organic-matter soils or species indifferent to forest age. Within species, the protease activities of ecotypes from soils with high or low soil organic N content did not differ significantly, suggesting resource partitioning between mineral and organic soil layers. The secreted protease mixtures were strongly dominated by aspartic peptidases. Glucose addition had variable effects on secreted protease activity; in some species, it triggered activity, but in others, activity was repressed at high concentrations. Collectively, our results indicate that protease activity, a key ectomycorrhizal functional trait, is positively related to environmental N source availability but is also influenced by additional factors, such as carbon availability.
authors.affiliation: Centre for Environmental Sciences, Environmental Biology Group, Hasselt University, Hasselt, Belgium francois.rineau@uhasselt.be.
authors.forename: Francois
authors.initials: F
authors.lastname: Rineau
authors.affiliation: Centre for Environmental Sciences, Environmental Biology Group, Hasselt University, Hasselt, Belgium.
authors.forename: Jelle
authors.initials: J
authors.lastname: Stas
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota, USA.
authors.forename: Nhu H
authors.initials: NH
authors.lastname: Nguyen
authors.affiliation: Department of Soil Quality, Wageningen University, Wageningen, The Netherlands.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kuyper
authors.affiliation: Centre for Environmental Sciences, Environmental Biology Group, Hasselt University, Hasselt, Belgium.
authors.forename: Robert
authors.initials: R
authors.lastname: Carleer
authors.affiliation: Centre for Environmental Sciences, Environmental Biology Group, Hasselt University, Hasselt, Belgium.
authors.forename: Jaco
authors.initials: J
authors.lastname: Vangronsveld
authors.affiliation: Centre for Environmental Sciences, Environmental Biology Group, Hasselt University, Hasselt, Belgium.
authors.forename: Jan V
authors.initials: JV
authors.lastname: Colpaert
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota, USA.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kennedy
mesh_terms: D001487:Basidiomycota / Q000201:enzymology / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D038821:Mycorrhizae / Q000201:enzymology / Q000378:metabolism*; D009584:Nitrogen / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D010447:Peptide Hydrolases / Q000378:metabolism*; D059748:Proteolysis; D012987:Soil / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D012987:Soil; D010447:Peptide Hydrolases; D005947:Glucose; D009584:Nitrogen