Close Encounters

Grasses invading a sub-Antarctic Island respond to rising temperatures, at a cost

Changing temperatures on Marion Island will remove restraints holding back invasive grasses.

Grasses invading the sub-Antarctic Marion Island are adapting better to rising temperatures. A team of South African researchers have found that the invasive species have greater plasticity, meaning they can change to cope with the warmer climate brought by global warming. However, this plasticity has a cost, the same species lose chilling tolerance.

The study took place on Marion Island 290 km2 of land a thousand miles south-east of South Africa. While 46 degrees south may not seem extreme, the island lies in the Roaring Forties. Any day of the year could bring snow, so the island is more tundra than temperate in climate. Being able to thrive in such conditions needs a special set of traits, and this was fine. But the native plants are now running into trouble.

“Surviving in cold terrestrial environments such as those of the sub-Antarctic requires a suite of traits, morphological and physiological, that confer stress tolerance. The selection of stress tolerance traits can limit phenotypic plasticity and the ability to survive and compete under conditions of changing climate,” write Brad Ripley and colleagues. The very traits that have enabled plants to survive in the Roaring Forties, have left them susceptible to competition from new arrivals.

Ripley and colleagues investigated what the situation facing the plants was by measuring measuring the photosynthetic response to warming, chilling tolerance and specific leaf area (SLA) of Pooid grasses.

“The invasive species responded to warm temperatures irrespective of acclimation, while the non-spreading species did not. The ability to respond immediately to warm temperatures suggests a greater phenotypic plasticity, which would be advantageous under climatic conditions where warm episodes are sporadic and not sustained over long periods (several days),” said the authors.

The downside for the invasive species is they lack the tolerance for chilling that the native species have developed. But this might be less of a problem for them in coming years.

“The recent warming with increased daily maxima and minima, and the concomitant decrease in the frequency of chilling events, appears to have decreased the need for chilling tolerance while giving an advantage to invasive species that are chilling sensitive, but have higher productivity and are able to respond to warming without acclimation.”

The results show that species from warmer climates could become invasive in the sub-Antarctic with climate change. As a lot of animal life either eats, or builds its life in these grasses, such a change could have impacts up the food pyramid and impact the whole ecosystem.

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