Positive and negative interactions on a dioecious grass species performance

Dioecious plants are of particular concern in view of global environmental changes because reproductive females are more sensitive to abiotic stresses, thus compromising population viability. Positive interactions with other plants may counteract the direct effects of any abiotic environmental stress, allowing them to thrive and maintain a viable population in suboptimal habitats, although this process has not been tested for dioecious species. Furthermore, almost no data are available on the outcome of such species interactions and their link with local spatial patterns and sex ratios.

Graff et al. find that facilitation, mediated by shrub canopies, help females of the native dioecious grass Poa ligulari (Poaceae) to grow and persist in an arid Patagonian steppe. However, water depletion by shallow-rooted shrubs prevents females from benefitting from favourable conditions aboveground. The importance of this facilitation/competition balance is reflected in female and male plants spatial distribution. Graff et al. argue that changes in benefactor species abundances could also impact in dioecious population viability.