Seedling recruitment in the semi-arid Patagonian steppe: facilitative effects of refuse dumps of leaf-cutting ants.

摘要

A study was conducted in northwestern Patagonia, Argentina, to investigate the influence of refuse dumps of leaf-cutting ants on seedling recruitment under contrasting moisture conditions in a semiarid steppe. In a greenhouse experiment, we monitored seedling recruitment in soil samples from refuse dumps of nests of the leaf-cutting ant Acromyrmex lobicornis and non-nest sites, under contrasting moisture conditions simulating wet and dry growing seasons. The mean number of seedling species and individuals were higher in wet than in dry plots, and higher in refuse dump plots than in non-nest soil plots. The positive effect of refuse dumps on seedling recruitment was greater under low moisture conditions. Both the accumulation of discarded seeds by leaf-cutting ants and the passive trapping of blowing-seeds seems not explain the increased number of seeds in refuse dumps. Conversely, refuse dumps have higher water retention capacity and nutrient content than adjacent non-nest soils, allowing the recruitment of a greater number of species and individual seedlings. Nests of A. lobicornis may play an important role in plant recruitment in the study area, allowing a greater number of seedlings and species to be present, hence resulting in a more diverse community. Moreover, leaf-cutting ant nests may function as nurse elements, generating safe sites that enhance the performance of neighbouring seedlings mainly during the driest, stressful periods.