title: Nitrogen deposition but not ozone affects productivity and community composition of subalpine grassland after 3 yr of treatment.
abstract: A field experiment was established at 2000 m above sea level (asl) in the central Swiss Alps with the aim of investigating the effects of elevated ozone (O(3)) and nitrogen deposition (N), and of their combination, on above-ground productivity and species composition of subalpine grassland. One hundred and eighty monoliths were extracted from a species-rich Geo-Montani-Nardetum pasture and exposed in a free-air O(3)-fumigation system to one of three concentrations of O(3) (ambient, 1.2 x ambient, 1.6 x ambient) and five concentrations of additional N. Above-ground biomass, proportion of functional groups and normalized difference vegetation index (NDVI) were measured annually. After 3 yr of treatment, the vegetation responded to the N input with an increase in above-ground productivity and altered species composition, but without changes resulting from elevated O(3). N input > 10 kg N ha(-1) yr(-1) was sufficient to affect the composition of functional groups, with sedges benefiting over-proportionally. No interaction of O(3) x N was observed, except for NDVI; positive effects of N addition on canopy greenness were counteracted by accelerated leaf senescence in the highest O(3) treatment. The results suggest that effects of elevated O(3) on the productivity and floristic composition of subalpine grassland may develop slowly, regardless of the sensitive response to increasing N.
authors.affiliation: Air Pollution and Climate Group, Agroscope Research Station ART, CH-8046 Zurich, Switzerland.
authors.forename: Seraina
authors.initials: S
authors.lastname: Bassin
authors.affiliation: Air Pollution and Climate Group, Agroscope Research Station ART, CH-8046 Zurich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Volk
authors.affiliation: Institute of Integrative Biology, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Suter
authors.affiliation: Institute of Plant Sciences, ETH Zurich, CH-8092 Zurich, Switzerland.
authors.forename: Nina
authors.initials: N
authors.lastname: Buchmann
authors.affiliation: Air Pollution and Climate Group, Agroscope Research Station ART, CH-8046 Zurich, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Fuhrer
mesh_terms: D018533:Biomass; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D010126:Ozone / Q000378:metabolism*; D006109:Poaceae / Q000378:metabolism*
chemical_list: D010126:Ozone; D009584:Nitrogen