Rasgos funcionales y plasticidad fenotípica de plantas exóticas invasoras

Abstract

This PhD thesis addresses the study of the functional traits and phenotypic plasticity that are ssociated to the invasibility of alien plant species and their impact in mediterranean ecosystems. The main objectives were: i) to search for differences between invasive and native phenotypes for an ample group of morphological and physiological traits, ii) to determine whether high phenotypic plasticity is associated to the invasibility of alien plant species, iii) to establish whether leaf traits that are related to the performance of invasive species influence nutrient cycling through litter decomposition, and iv) to study whether the flowering phenology differences between invasive and native species is a trait that confers invasiveness. Morphological and physiological responses of 31 traits to two gradients of light and nutrient availability were studied in 20 invasive-native pairs (chapter 2). For the third objective, initial litter trait, litter decomposition rates and the relative importance of initial litter traits in litter decomposition were compared within 19 invasive-native pairs (chapter 3). Finally, we compared the flowering phenology of invasive and native species in three mediterranean-type ecosystems searching the flowering phenology data of 227 invasive-native pairs (chapter 4 and 5). Results showed that high light and nitrogen use efficiencies confer invasibility to alien species, resulting in a enhance fitness when they are grown in light and nutrient gradients. However the water use efficiency of alien species was low, which could limit their invasion of Spanish mediterranean ecosystems to areas where the abiotic filter of summer drought is minimised. Contrary to expectations, invasive species displayed the same or even lower levels of phenotypic plasticity compared to natives. However, a highly competitive phenotype allows invasive species to obtain a higher fitness increment per unit of plastic response compared to natives. Therefore, high plasticity efficiency seems to be a trait that confers invasibility to alien plant species. Invasive species had higher lignin content in leaf litter. Invasive species were more nitrogen- and phosphorus-dependent for their decomposition due to their higher lignin content. Because lignin is difficult to degrade, the rate of litter decomposition was lower in invasive species compared to natives, suggesting that under natural conditions nutrient cycling can be slow down upon invasion. The later flowering phenology of invasive species compared to natives in Spanish mediterranean ecosystems is not a common pattern in other mediterranean-type ecosystems such as the Cape Region of South Africa and California, where invasive species flower earlier or at the same time than natives, respectively. Thus, a different flowering phenology between invasive and native species is not a trait associated with invasiveness. However, it determines the most likely growth form of invasive species. In this sense, summer-flowering limits the invasion of alien species to habitats with water availability during summer where fast-growing herbaceous are adapted to live.