No abstract

Plant litter decomposition is critical for terrestrial ecosystem productivity. Poa ligularis Nees ex Steud and Nassella tenuis (Phil.) Barkworth are native, desirable perennial grasses in central Argentina’s rangelands. Amelichloa ambigua (Speg.) Arriaga & Barkworth is only consumed when a better forage is unavailable. Litter traps were used to collect aboveground litter during two years. In March 2012, six bags, each one containing either leaf blade (three bags, one per species) or root litter (three bags, one per species) of the three species were located below the canopy of each replicate plant of the studied species (hereafter referred to as ‘location’). Blade litter bags were located on the soil surface, and root litter bags buried at 10cm soil depth. This allowed evaluation of the effects of defoliation, the different species canopies and the microbial community activity around their roots on decomposition of above- and belowground litter. For each species, twenty plants were either defoliated twice (5cm stubble height) or remained undefoliated during the growing season. Litter bags were collected after 2, 7, 13 and 24 months incubation. The study was repeated in 2013, with additional bags were placed for N content determination on leaf blade and root litters. Aboveground litter production was highest in P. ligularis; however, no differences were observed among species when the effect of plant size was eliminated. Aboveground litter of desirable species had higher N content and decomposed faster than that of A. ambigua. The opposite was recorded for root litter. Defoliation had no effect on litter decomposition, but location effects were detected after one year of incubation. Desirable perennial grasses promoted organic matter loss from litter, a key factor in increasing soil fertility in this semiarid ecosystem.

No abstract

The field performance of the native Pappophorum vaginatum, the naturalized Eragrostis curvula and various cultivars of the introduced Achnatherum hymenoides and Leymus cinereus was evaluated as potential forage resources in rangelands of arid Argentina during the warm seasons of 2007/2008 and 2008/2009. Plants of these grass species, obtained from seeds, were transplanted to the field in 2006, when they were 1 year old. During the study years, there were two defoliation managements: plants of all study genotypes either remained undefoliated (controls) or were defoliated twice a year during spring at 5 cm stubble height. Despite tiller number being lower (P < 0·05) on defoliated than on undefoliated plants, and total leaf length per unit basal area being similar (P > 0·05) between defoliation managements by mid‐spring, there were no differences (P > 0·05) in dry weight production between defoliated and undefoliated plants in all genotypes at the end of the second growing season. Plants of one or more of the introduced genotypes showed a similar (P > 0·05) or greater (P < 0·05), but not lower, tiller number per plant and per square centimetre, daughter tiller production, total leaf length and dry weight production per unit basal area than the native species at the end of the first and/or second growing seasons. These morphological variables were similar (P > 0·05) or greater (P < 0·05) in the native than in the naturalized genotype. Plant survival, however, was lower (P < 0·05, overall mean = 20%) in the introduced than in the native (>70%) or naturalized (>39%) genotypes at the end of the first or second growing seasons.