Effects of leaf-cutting ant refuse on native plant performance under two levels of grazing intensity in the Monte Desert of Argentina

CERDA, N.V.; TADEY, M.; FARJI-BRENER, A. G.; NAVARRO, M. C.

APPLIED VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2012 vol. 15 p. 479 - 487

1402-2001

Question: Low quantities of soil nutrients often restrict plant establishment and growth in arid lands and have been partially attributed to the scarcity of organic matter in these ecosystems. Thus, increasing the amount of soil organic matter is a key issue in attempts to restore and manage a desired plant cover, especially in arid ecosystems. Refuse dumps from leaf-cutting ants are a natural source of organic matter. However, their effects on native plant performance have received limited attention to date. We experimentally determined whether refuse dumps from lea-cutting ants  (Acromyrmex lobicornis) can be used to enhance the germination and growth of several native plant species and analyzed the potential influence of heavy grazing on this practice.Location: Monte Desert, Neuquén Province, Argentina. Methods: We collected fruits of five plant species and two types of substrates (ant refuse dump vs. control soil) from two known paddocks with different livestock densities (high vs. low). We sowed seeds, previously weighed, of each species in both substrates from both paddocks and monitored their development. We harvested emerged seedlings, documenting their age and measured their height, weight, number of leaves, root weight and root length.Results: Seed weight was lower in the highly grazed paddock for all the plant species studied. However, seed weight did not affect germination rate. Refuse dump material increased germination rate of all plant species, especially when this substrate came from the less grazed paddock (i. e., with more nutrient content). Also, germination improved when both seeds and substrates were from the less grazed paddock. Vigor variables showed more complex results, but seedlings growing in refuse dumps tended to be more vigorous. Particularly, refuse dumps from the less grazed paddock (i.e., with more nutrient content) enhanced more seedlings vigor of smaller seeds, those from the highly grazed paddock.Conclusions: Our results demonstrated that ant refuse dumps have the ability to increase germination rate in plants and improve the performance of the most representative vegetation in the Monte Desert. Given that external refuse dumps from leaf-cutting ants are a renewable resource, very abundant and easy to collect, this substrate can be used as a free natural fertilizer in arid regions to restore and manage vegetation cover, especially in heavily grazed sites.