Palatable grasses have higher Relative Growth Rate and competitive ability than unpalatable grasses in the Patagonian steppe.

GARCÍA MARTÍNEZ G.C. Y GOLLUSCIO R.A.

Hohhot, China

Congreso; XXI International Grassland Congress- VIII International Rangeland Congress.; 2008

Internacional Rangeland Society

Introduction:   In Patagonia, sheep grazing triggered processes of desertification of different magnitude (León y Aguiar 1985). In the Patagonian shrub-grass steppe, grazing caused a clear substitution of palatable species by unpalatable ones (Perelman et al. 1997). Coughenour (1985) proposed that exist an evolutionary convergence between those adaptations allowing plants to tolerate water and nutrient deficits, and those confering tolerance against herbivores. Plant populations evolved under severe resource limitations would have low relative growth rates and adaptations against both nutrient and water deficits and also against herbivory (Chapin et al. 1993). The objective of this work was to evaluate the relative growth rate (RGR), water consumption and competitive ability of two grass species of the Patagonia steppe with contrasting palatability.   Materials and methods:   We performed an experiment under glasshouse conditions, with a factorial arrangement that included three factors: species (Bromus pictus, palatable,  vs.  Stipa speciosa, unpalatable), competition (intraspecific vs. interspecific) and water availability (constant field capacity vs. initial field capacity without any posterior watering). We harvested aerial parts and measured soil water content at 81 and 102 days before emergence.   Results:   Palatable B. pictus showed a greater RGR than unpalatable S. speciosa in the interval between the beginning of the experiment and the first harvest (0-1) and in the average of all the experiment (0-2) while there were no between-species differences in the interval between the first and the last harvest (1-2) (Figure 1).  Accordingly, the palatable species had greater water consumption than the unpalatable one (p<0.05). Finally, the palatables species reached a greater number of tillers per plant when it grew under interspecific competition than when it did it under intraspecific competition. Instead, S. Speciosa showed the opposite response (Figure 2). Similar responses to those described for the tillers per plant were recorded in the number of total leaves, live leaves and aerial biomass per plant, supporting the hypothesis of a greater competitive ability of palatable B. Pictus over unpalatable S. speciosa. Conclusions:   Palatable B. pictus had greater maximum relative growth rate, water consumption and competitive ability than unpalatable S. speciosa.