Controls of aerial biomass, primary productivity and plant nutrient concentration in a temperate grassland

MARIANO OYARZABAL; MARTÍN OESTERHELD

Canberra

Congreso; Annual Conference of the Ecological Society of Australia; 2010

Descriptions of ecosystem functioning in relation to single factors are common. However, environmental changes are inherently multifactorial and their impact depends on how ecosystems respond to multiple factors. A factorial experiment was conducted in a Pampean grassland that is active throughout the year, with the objective of studying the effect of environmental factors on aerial green biomass, aerial net primary productivity (ANPP), and N and P concentration in biomass. The experiment involved Nitrogen level as one factor interacting with either P fertilization, defoliation, shading, warming, or summer watering. The only significant interactive effects were an increase of biomass in summer with N and P fertilization and a reduction of biomass when the grassland was defoliated without N fertilization. Independently on nitrogen level, defoliation reduced biomass in autumn and winter and increased N concentration in winter. N fertilization increased ANPP in spring and summer and N concentration in summer and winter. P fertilization only increased P concentration during all seasons. Finally, warming increased biomass during autumn. Three species? functional groups differentially accounted for these ecosystem-level responses. In summary, functioning of this grassland was controlled mainly by defoliation and/or fertilization, and the effects varied among seasons and functional groups.