Nitrogen deposition but not ozone affects productivity and community composition of subalpine grassland after 3 yr of treatment
2007
Bassin, Seraina | Volk, Matthias | Suter, Matthias | Buchmann, Nina | Fuhrer, Jürg
• 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 (O₃) 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 O₃‐fumigation system to one of three concentrations of O₃ (ambient, 1.2 × ambient, 1.6 × 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 O₃. 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 O₃ × N was observed, except for NDVI; positive effects of N addition on canopy greenness were counteracted by accelerated leaf senescence in the highest O₃ treatment. • The results suggest that effects of elevated O₃ on the productivity and floristic composition of subalpine grassland may develop slowly, regardless of the sensitive response to increasing N.
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