Intra and interspecific interactions between an endangered cactus and shrubs in the hyper-arid Monte desert of Argentina

ALMIRÓN, M.; E. MARTINEZ CARRETERO

AUSTRAL ECOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2013

1442-9985

The spatial intraspecific and interspecific distribution of P. sanjuanensis (Speg.) Backeb was studied at landscape scale in three physiographic units and at micro-scale in terms of position under shrubs found in those units. The influence of shrubs on photosynthetically active radiation and on soil temperature was analyzed. In laboratory assays, we also analyzed average percent and rate of germination in relation to both controlled conditions: constant temperature (20 and 30 °C) and light (12/12 h light vs. darkness). The intraspecific distribution of P. sanjuanensis was random in all units. The interspecific distribution was highly associated with dominant shrubs (Larrea cuneifolia and/or Zuccagnia punctata) in each physiographic unit, observing decreasing gradients of association from the center toward the edge of shrub canopies, coinciding with both the light and temperature gradients detected under those nurse shrubs. The effect of light on germination would indicate positive photoblastism. The low germination rate and the associations with specific shrubs suggest that the exclusive reproduction by seed germination could be crucial in the final distribution of this cactus. This endemic species is considered to be in a high-risk category due to its restricted geographical distribution and the high impact by human activities, like extraction, and by activities affecting its natural populations (mining, uncontrolled waste deposits, fire and cutting of nurse plants, among others). In desert environments, the interaction between species is a strategy that allows survival of several plants. For this reason, the study of interactions between P. sanjuanensis and specific shrubs is decisive. Some protection strategies can be suggested, like conservation of associated shrubs, and ex-situ germination improvement for future reintroduction. The analysis of explicit spatial patterns, considering both intra and interspecific relations between a target species and all potential nurse plants, allows us to improve our view of desert plant interactions.