IFEVA   02662
INSTITUTO DE INVESTIGACIONES FISIOLOGICAS Y ECOLOGICAS VINCULADAS A LA AGRICULTURA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Effect of the rainfall interannual variability on Patagonian Grass Steppe
Autor/es:
MASSARA PALETTO V.; SEMMARTIN M.; YAHDJIAN ML; BUONO G
Lugar:
Rosario
Reunión:
Congreso; IX Congreso Internacional de Pastizales; 2011
Institución organizadora:
International Rangeland Congress
Resumen:
Introduction: Aerial Net Primary Production (ANPP) largely depends on precipitation and constrains both secondary production and range management decisions. One of the best documented relationship in grassland ecology is the linnear and positive response of primary productivity to precipitation. Moreover, models that describe the changes in productivity over time for a given site (temporal model) show that the increase of ANPP per millimeter of precipitation is smaller than models that relate different sites on a spatial precipitation gradient (spatial model). In addition, recent studies indicate that the response of ANPP to precipitation would be asymmetric since the reduction in ANPP observed during dry years is lower than the increases observed during wet years. The objective of this study was to evaluate the effects of interannual water availability on ANPP and phenology of main species of a semi-arid grassland in Patagonia. Materials and Methods: We performed a manipulative water experiment in the Patagonian steppe, South of Argentina, and measured grasses ANPP during three years. We created a water availability gradient with 5 levels, two levels of drought (with interceptio of 30 and 50% of rainfall), two irrigation levels (with the addition of 30 and 50% more water than actual precipitation) and a control level (actual rain fall of the site) (Figure 1). We quantified the cover of different grassland components, the aerial productivity of dominant grass species and the phenology of the more representative species (grasses and a shrub), in a site temporarily fenced to grazers. Results and Discussion: The three consecutive-years field experiment showed increasing responses of ANPP along the experimental precipitation gradient with time (Figure 2). The first year drought and irrigation affected litter cover and bare soil, with more bare soil on drought treatments (p<0.05), while cryptogrammic had significantly more coverage on irrigation treatments (p=0.06). However, grass primary productivity was not affected by water availability (p=0.59). Plant phenology showed changes in the duration of the phases that did not follow the same pattern for all species. During the second year, grasses productivity dropped by almost half and showed a linear and positive response to precipitation (p=0.002) given by the response of the dominant grass species. Finally, during the third year, we found an increased response to water availability (p=0.06) again influenced by the dominant species. The third year was particularly wetter than the others two, and control plots received more favorable conditions during this third year. All plots showed an increased response to more humid conditions, which suggest the asymetric response to more humid years previously described. These results suggest a greater grassland buffer to a first dry year and a great ability to respond to favorable conditions during a wet year. Also, we provide valuable basic information on dominant species to one of the most important control in Patagonian steppe, water availability, that will allow us to develop decision strategies on emergency situations.