The effect of heavy metal contamination pre-conditioning in the heat stress tolerance of native and invasive Mediterranean halophytes

Salt marshes are worldwide recognized for their unique and important ecological role. According to the Intergovernmental Panel on Climatic Change (IPCC), the frequency and intensity of warming events will rise due to global changes. Halophyte plants, inhabiting salt marshes are known for being highly tolerant to various abiotic stresses, nonetheless, although it has been acknowledged that the tolerance response is species specific there could also be differences at the population level. The present work aims to determine if the life history of two halophytes (Halimione portulacoides and Spartina patens), namely in terms of contaminant exposure, influences inter-populational heat tolerance. For this purpose, individuals from both species collected at pristine and contaminated sites were exposed to normal and increased temperature conditions, and its physiological fitness evaluated throughout biochemical and biophysical analysis. The photobiological traits, pigment and fatty acid profiles and oxidative stress biomarkers analyses of warming treated individuals, indicate that chronic heavy metal pre-conditioning significantly influences the heat stress tolerance of the native halophyte plants. Halimione portulacoides individuals collected at heavy metal contaminated salt marsh appeared more tolerant to heat stress. On the other hand, the invasive S. patens from the pristine site showed higher tolerance to heat stress. Thus, the pre-conditioning influences the tolerance mechanisms can affect the way in which salt marsh communities will evolve in the future, possibly being different through salt marshes. The contaminated marsh can be more resilient to invasion than the non-contaminated marsh, since the native species has benefited from this pre-conditioning. Moreover, and from the ecophysiological point the set of biophysical and biochemical indicators were tested, show a high efficiency in describing the ecophysiological traits, both between species and populations, facing different pre-conditioning histories.