Abstract

ANSIN, Oscar E; DEREGIBUS, Alejandro  and  LANFRANCO, Jorge W. Role of the blue green alga Nostoc commune and effect of cattle grazing on plant colonization of alkaline soils of the Flooding Pampa. Ecol. austral [online]. 2002, vol.12, n.2, pp.135-142. ISSN 1667-782X.

Nostoc commune (Vauch.), a blue green algae that influences soil fertility through atmospheric nitrogen fixation, is common in alkaline soils of the Flooding Pampa, Argentina. The objectives of this work were to evaluate the relationship between the presence of Nostoc commune, plant germination and seedling emergence, as a way to understand whether or not Nostoc commune plays a significant ecological role in the colonization process of bare alkaline soils. More seedlings were observed in micropatches covered with algae during autumn, winter and spring, being recorded maximum seedling abundance (68.3 seedlings/dm²) in microdepressions with algae. More seeds of Hordeum pusillum (Steud.), an annual grass conspicuous to these alkaline soils, germinated under greenhouse conditions when were placed either above or under algae Nostoc commune. The soil below the algae showed lower pH values and higher organic matter, carbon and nitrogen content. Cattle grazing had an impact on both algae and plant cover. We concluded that the presence of algal crusts has a significant ecological impact in these alkaline soils, as it improves soil properties and stimulates germination, seedling establishment and persistence of annual plants. Through controlled cattle grazing management is possible to promote the presence of Nostoc commune and enhance habitat quality.

Keywords : Plant colonization; Nostoc commune; Natural grasslands; Cattle grazing; Seedling establishment.

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