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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.

In the Monte Austral Neuquino, Argentina, vegetation is arranged in patches. Understanding the mechanisms involved in their distribution is critical for preventing desertification. The working hypothesis was that vegetation patches reduce environmental stress on the plants. Plant patches were classified into four microenvironments: windward; below the dominant shrubs (subcanopy); vegetation at the patch periphery (canopy edge) and bare patch interspaces (open). We determined seedling survival of the dominant species in each microenvironment, using a marking method of seedlings established from sown seeds. In addition, we measured the environmental characteristics in the four microenvironments, and associated them with seedling survival. Study species were the perennial grasses Leymus erianthus (Phil.) Dubcovsky, Stipa neaei Nees ex Steudel and Poa ligularis Nees ex Steudel, and the shrubs Larrea divaricata Cav. and Atriplex lampa Gill ex Moquin. Results supported the hyphothesis only for L. erianthus and S. neaei (but not for the other three species that showed higher seedling survival in the subcanopy than in the patch interspaces after 1 year from sowing). This study determined that (1) reduced environmental stress does not guarantee seed germination and seedling survival of a given species in the plant community and (2) seedling establishment will not be possible for any species of the plant community in the patch interspaces under the study conditions in the region. This is mostly because soil temperatures can reach up to 50°C in the patch interspaces in years of scanty precipitation during late spring and summer. Copyright © 2010 John Wiley & Sons, Ltd.

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