Ecophysiology of the invader Pennisetum setaceum and three native grasses in the Canary Islands

Pennisetum setaceum (fountain grass) is an aggressive invader in the arid and semi-arid habitats of the tropics and subtropics. In the last twenty years the spread of fountain grass in the Canary Islands has been very rapid. We compared its ecophysiological, architectural and reproductive traits with those of three native grasses (Hyparrhenia hirta, Cenchrus ciliaris and Aristida adscensionis) in two habitats of Tenerife Island which differ in rainfall. The detection of traits that differ between native and invader grasses may provide information for the improved control and eradication of the latter contributing to protect the native plant diversity. P. setaceum and the native grasses differed in all measured traits and in their response to water availability which is more restricted in the southern site. Specific leaf area was lower in P. setaceum than in the native grasses. Although this reduces carbon assimilation per unit area, it also reduces transpiration, increasing water use efficiency and contributes to the maintenance of high relative water content. Leaf N in P. setaceum was lower than in the native grasses indicating higher nitrogen use efficiency. The activity of photosystem II was higher and lasted longer in P. setaceum than in the native grasses. The ecophysiological traits of P. setaceum support its large size, extensive canopy and shorter leaf senescence period. They confer considerable competitive advantage to the invader and partially explain its success in the Canary Islands. The differences between the invader and the native grasses were maintained in both sites revealing a good adaptation of P. setaceum to the low resource local habitats in the Canary Islands and confirms its large plasticity. The large invasive potential of P. setaceum, in concert with the projected global changes, forecast eventual risks for the conservation of the endemic flora and remaining native communities in the Canary Islands.