Biomass production is more limited by P than N, but N strongly reduced plant diversity in a highly-productive grassland.

TOGNETTI, P.; GRAFF, PAMELA; YAHDJIAN, LAURA; CHANETON, E.J.

Louiville

Congreso; 104th Annual Meeting of the Ecological Society of America; 2019

Ecological Society of America

Background/Question/MethodsNative grassland productivity is generally nitrogen (N) limited, although the prevalence of phosphorus (P) limitationis increasingly recognized. However, the magnitude of multiple limitation by N, P, and other nutrients remains poorlyunderstood in natural grasslands, despite that they account for approximately one-third of Earth?s terrestrial netprimary production. In addition, increasing nutrients loads in grasslands may trigger the loss of plant speciesthrough a reduction in light availability, and foster the dominance of invasive exotic species. Here we assessed theco-limitation by nutrients of biomass production and plant species composition through a field experiment in ahighly-productive grassland in the Flooding Pampa, Argentina. The design was a complete factorial of nitrogen,phosphorus and potassium +micronutrients addition as main effects, paired with unfertilized control plots (total=8treatments). Fertilizer (NPK) was applied three times a year to 5 m x 5 m plots established within 3 un-grazedexclosures (total = 24 plots). Biomass production was estimated by clipping 0.1 m2 during peak biomass along 5consecutive experimental years since 2012. Diversity was estimated by the number of species (richness) and theeffective richness (eH) indexes, both calculated from 1 m2 species cover data in spring and summer.Results/ConclusionsP and N significantly increased biomass production, although P addition showed the biggest increase (25% and20% for P and N respectively). Indeed, all combinations containing P produced more biomass across the 5experimental years than controls, but the effects were partially additive. K +micronutrients addition showed noresponse in plant biomass. The plots that showed the highest biomass increase since the pre-treatment conditionwere also those containing the highest abundance of Festuca arundinacea, a dominant exotic grass (r2=0.17;p