title: Soil environmental conditions and microbial build-up mediate the effect of plant diversity on soil nitrifying and denitrifying enzyme activities in temperate grasslands.
abstract: Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number - namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification.
authors.affiliation: Université de Lyon, INRA, CNRS, Université Lyon 1, Microbial Ecology Centre, UMR 5557 CNRS, USC 1364 INRA, Villeurbanne, France. Xavier.le-roux@univ-lyon1.fr
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Roux
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schmid
authors.forename: Franck
authors.initials: F
authors.lastname: Poly
authors.forename: Romain L
authors.initials: RL
authors.lastname: Barnard
authors.forename: Pascal A
authors.initials: PA
authors.lastname: Niklaus
authors.forename: Nadine
authors.initials: N
authors.lastname: Guillaumaud
authors.forename: Maike
authors.initials: M
authors.lastname: Habekost
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Oelmann
authors.forename: Laurent
authors.initials: L
authors.lastname: Philippot
authors.forename: Joana Falcao
authors.initials: JF
authors.lastname: Salles
authors.forename: Michael
authors.initials: M
authors.lastname: Schloter
authors.forename: Sibylle
authors.initials: S
authors.lastname: Steinbeiss
authors.forename: Alexandra
authors.initials: A
authors.lastname: Weigelt
mesh_terms: D000704:Analysis of Variance; D044822:Biodiversity; D058440:Denitrification; D017753:Ecosystem; D004798:Enzymes / Q000378:metabolism; D007887:Fabaceae / Q000382:microbiology; D058465:Nitrification; D006109:Poaceae / Q000382:microbiology*; D012044:Regression Analysis; D012988:Soil Microbiology
chemical_list: D004798:Enzymes