Plant litter decomposition in a semi-arid rangeland of Argentina: species and defoliation effects

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 10 cm 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 (5 cm 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.