Recruitment patterns in four species of Physaria (Brassicaceae): implications for maintenance of population density over time in both native and cultivated stands

Abstract

Seedling recruitment is a critical stage of a plant’s cycle which determines population viability, the potential for invasiveness of a plant species and the success of establishment of a crop, among other processes. We evaluated the most relevant stages leading to recruitment (seed-rain, the time of seedling emergence, and seedling survival) in four species of Physaria (P. gracilis, P. angustifolia, Physaria pinetorum and P. mendocina) in a field experiment in Patagonia, Argentina, to assess the possibility of using spontaneous recruitment to understand population dynamics and to evaluate the potential of this process as a tool for crop reestablishment. We determined the effect of water availability and initial seedling density on final stand density. The total amount of dispersed seed was higher in P. gracilis and P. pinetorum than in the other two species. Physaria pinetorum germinated in late summer, while P. angustifolia and P. gracilis germinatedin spring. No germination was registered for P. mendocina. In the three species whose seeds germinated, seedling survival was modulated by a density-dependent mechanism. For P. pinetorum seedling density was stable over time in low-density plots, while it decreased in high- and medium-density plots. Still, the highest final density was found in those plots with high initial density. Final density of P. gracilis also responded to irrigation treatment. The amount of dispersed seeds was adequate for the re-establishment of the crop in all four species, although the following stages were species-dependent. An appropriate control of seedling density at the initial stage of crop establishment may play a relevant role in the proper regeneration of the crop.