Seasonal variation in the leaf physiology of co-occurring invasive (Hakea sericea) and native (Pinus pinaster) woody species in a Mediterranean-type ecosystem

Abstract Physiological traits are critical factors in species invasion success. It is generally accepted that invasive alien species (IAS) are more efficient at resource acquisition and/or use than are native species. However, in the case of the invasive Hakea sericea, the importance of such mechanisms remains unexplained. This gap in extant knowledge has prompted the present study, in which the main objective was contrasting the physiological performance of Hakea sericea with the native Pinus pinaster in Mediterranean-climate ecosystems. Leaf gas exchange, photosynthetic pigments, metabolites and water relationships were measured seasonally during one year, revealing a pronounced seasonal variation in all parameters. Overall, stomatal conductance (gs) peaked in spring, whereas intrinsic water use efficiency (WUE) reached its maximum in autumn. The highest photosynthetic rate (A) was detected in autumn and summer. Across the year, Hakea sericea displayed higher relative water content (RWC), A and WUE values than Pinus pinaster. Moreover, the IAS presented higher leaf total chlorophyll and soluble sugars. In turn, leaves of the native species had values of starch and proteins higher than the IAS. Therefore, compared with Pinus pinaster, Hakea sericea exhibits superior physiological performance mainly supported by an efficient use of resources and greater photosynthetic capacity. These characteristics are likely responsible for its invasion success in Mediterranean ecosystems. In addition, they could confer a significant competitive advantage in a changing climate, as well as enable this species to outcompete native species, resulting in increased abundance and more significant impact on ecosystems.