Plant traits contributing to the performance of native and introduced rangeland grasses in arid Argentina

Abstract

Rangelands from central Argentina characterize by insufficient warm-season, palatable perennial grasses to domestic livestock. Two palatable and water-stress tolerant cultivars ("Magnar" and "Trailhead") of Leymus cinereus were introduced into Argentina with the purpose of increasing the warm-season forage offer. Some mechanisms involved in determining defoliation tolerance and competitive ability, and subsequent dry matter production, were investigated in the study genotypes. Studies were conducted within an exclosure to domestic livestock. Two severe defoliation treatments were applied in 2006/07 and 2007/08. Only Pappophorum vaginatum, the native genotype, produced and dispersed seeds. Natural water stress during the second study year advanced phenology of all three genotypes. This advancement, together with the high production of total, reproductive and daughter tillers in P. vaginatum, even under defoliation, might contribute to explain its greater abundance than the other native, warm-season perennial grasses in rangelands of central, arid Argentina. Although plant survival and forage production were lower (p<0.05) on the introduced cultivars than in the native genotype, Leymus genotypes showed greater (p<0.05) total (green + dry) leaf numbers/cm2, total green sheath lenght/cm2, and arbuscular mycorrhiza (AM) colonization percentages than P. vaginatum. Root length densities, total (green + dry) leaf length and leaf blade/sheath ratios were greater (p<0.05) or similar (p>0.05), but not lower, in the introduced than in the native genotype. Future research is needed to substantially improve plant establishment of L. cinereus, genotype which can be seeded by conventional drilling.