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Fungal endophyte associations have been suggested as a possible strategy of Antarctic vascular plants for surviving the extreme environmental conditions of Antarctica. However, the mechanisms by which this occurs are still poorly understood. The role of root fungal endophytes in nitrogen mineralization and nutrient uptake, as well as their impact on the performance of Antarctic plants, were studied. We tested root endophytes, isolated from Colobanthus quitensis and Deschampsia antarctica, for lignocellulolytic enzyme production, nitrogen mineralization, and growth enhancement of their host plants. Penicillium chrysogenum and Penicillium brevicompactum were identified using a molecular approach as the main root endophytes inhabiting C. quitensis and D. antarctica, respectively. Both root endophytes were characterized as psychrophilic fungi displaying amylase, esterase, protease, cellulase, hemicellulase, phosphatase and urease enzymatic activities, mainly at 4 °C. Moreover, the rates and percentages of nitrogen mineralization, as well as the final total biomass, were significantly higher in symbiotic C. quitensis and D. antarctica individuals. Our findings suggest that root endophytes exert a pivotal ecological role based not only to breakdown different nutrient sources but also on accelerating nitrogen mineralization, improving nutrient acquisition, and therefore promoting plant growth in Antarctic terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Antarctica is a stressful ecosystem with few vascular plants, an ideal system to test positive interactions. Here, plants such as Deschampsia antarctica could generate more suitable micro-environmental conditions for the establishment of other plants (facilitation). We examined the co-occurrence of vascular plant species in the Antarctic Peninsula and assessed the potential nurse effect by D. antarctica on the native Colobanthus quitensis and the invasive Poa annua. We also measured the ecophysiological performance and survival of C. quitensis within and outside the canopy of D. antarctica in two study sites differing in stress levels. In addition, a survival experiment was conducted with the invasive Poa annua individuals within and outside D. antarctica individuals. In sites where present, target species co-occurred with D. antarctica in both Shetland Islands and Antarctic Peninsula. In agreement with the stress gradient hypothesis, we found evidence of facilitation between vascular Antarctic plant species. Specifically, we found that D. antarctica facilitates the native C. quitensis and the invasive P. annua and that the effect is stronger in more stressful sites. Additionally, C. quitensis distribution is compatible with an influence of either direct or indirect facilitation from D. antarctica. Facilitation between vascular plants may play a role structuring Antarctic plant communities. Thus, distribution of native species should be considered when assessing the introduction and spread of invasive species. Also, our results together with those from previous studies showed that the type and magnitude of biotic interactions may change with time and can depend on the plant traits considered. [ABSTRACT FROM AUTHOR]

The two native Antarctic vascular plants, Deschampsia antarctica and Colobanthus quitensis, are mostly restricted to coastal habitats where they are often exposed to sea spray with high levels of salinity. Most of the studies regarding the ability of C. quitensis and D. antarctica to cope with abiotic stress have been focused on their physiological adaptations to tolerate cold stress, but little is known about their tolerance to salinity. We investigated whether rhizospheric bacteria associated to D. antarctica and C. quitensis improve the ability of Antarctic plants to tolerate salt stress. Salt tolerance was assayed in rhizospheric bacteria, and also their effects on the ecophysiological performance (photochemical efficiency of PSII, growth, and survival) of both plants were assessed under salt stress. A total of eight bacterial rhizospheric strains capable of growing at 4 °C were isolated. The strains isolated from D. antarctica showed higher levels of salt tolerance than those strains isolated from C. quitensis. The ecophysiological performance of C. quitensis and D. antarctica was significantly increased when plants were inoculated with rhizospheric bacteria. Our results suggest that rhizospheric bacteria improve the ability of both plants to tolerate salinity stress with positive effects on the adaptation and survival of vascular plants to current conditions in Antarctic ecosystem. [ABSTRACT FROM AUTHOR]

Antarctica is one of the less prone environments for plant invasions, nevertheless a growing number of non-native species have been registered in the last decades with negative effects on native flora. Here we assessed adaptive phenotypic plasticity in three photoprotective traits (non-photochemical quenching, total soluble sugars, and de-epoxidation state of xanthophylls cycle), and fitness-related traits (maximum quantum yield, photosynthetic rate and total biomass) in the invasive species Poa annua and Deschampsia antarctica under current conditions of water availability and those projected by climate change models. In addition, two manipulative experiments in controlled and field conditions were conducted to evaluate the competitive ability and survival of both species under current and climate change conditions. Moreover, we performed an experiment with different water availabilities to assess cell damage as a potential mechanism involved in the competitive ability deployed in both species. Finally, was assessed the plasticity and biomass of both species subject to factorial abiotic scenarios (water × temperature, and water × nutrients) ranging from current to climate change condition. Overall, results showed that P. annua had greater phenotypic plasticity in photoprotective strategies, higher performance, and greater competitive ability and survival than D. antarctica under current and climate change conditions. Also, cell damage, assessed by lipid peroxidation, was significantly greater in D. antarctica when grown in presence of P. annua compared when grown alone. Finally, P. annua showed a greater plasticity and biomass than D. antarctica under the factorial abiotic scenarios, being more evident under a climate change scenario (i.e., higher soil moisture). Our study suggests that the high adaptive plasticity and competitive ability deployed by P. annua under current and climate change conditions allows it to cope with harsh abiotic conditions and could help explain its successful invasion in the Antarctica. [ABSTRACT FROM AUTHOR]

The upper and poleward limit of tree distribution are usually determined by abiotic factors such as low temperature and strong winds. Thus, cold resistance is a key element for survival in high altitudes and latitudes where conditions can reduce plant growth. A trade-off between resource allocation to cold resistance and growth could emerge in populations frequently exposed to low temperatures like those in the treeline zone. We studied annual height growth and ice nucleation temperature in Nothofagus pumilio (Nothofagaceae) populations growing in its extremes of altitudinal distribution and in 3 sites situated on a latitudinal gradient in the Chilean Andes. Additionally, gas exchange, water and nitrogen use efficiency and total soluble sugar (TSS) were also measured as possible mechanisms for survival in high altitudes. Individuals from the treeline populations showed lower annual height growth and lower ice nucleation temperatures compared with those from lower populations. In the same way, individuals from more poleward populations showed lower annual height growth and lower ice nucleation temperatures. Gas exchange, water and nitrogen use efficiency and TSS were also higher in the high altitude populations. The results obtained support the hypothesis of trade-off, because the upper and poleward populations showed more cold resistance but a lower height growth. Additionally, we show that cold resistance mechanisms do not impact the physiological performance, suggesting possible adaptation of the high altitude populations. Low temperatures may be affecting cellular growth instead of photosynthesis, creating a pool of carbohydrates that could participate in cold tolerance. Other abiotic and biotic factors should be also assessed to fully understand the distributional range of Nothofagus species. [ABSTRACT FROM AUTHOR]

Ecological theory predicts a positive association between environmental heterogeneity of a given habitat and the magnitude of phenotypic plasticity exhibited by resident plant populations. Taraxacum officinale (dandelion) is a perennial herb from Europe that has spread worldwide and can be found growing in a wide variety of habitats. We tested whether T. officinale plants from a heterogeneous environment in terms of water availability show greater phenotypic plasticity and better performance in response to experimental water shortage than plants from a less variable environment. This was tested at both low and moderate temperatures in plants from two sites (Corvallis, Oregon, USA, and El Blanco, Balmaceda, Chile) that differ in their pattern of monthly variation in rainfall during the growth season. We compared chlorophyll fluorescence (photosynthetic performance), flowering time, seed output, and total biomass. Plants subjected to drought showed delayed flowering and lower photosynthetic performance. Plants from USA, where rainfall variation during the growth season was greater, exhibited greater plasticity to water shortage in photosynthetic performance and flowering time than plants from Chile. This was true at both low and moderate temperatures, which were similar to early- and late-season conditions, respectively. However, phenotypic plasticity to decreased water availability was seemingly maladaptive because under both experimental temperatures USA plants consistently performed worse than Chile plants in the low water environment, showing lower total biomass and fewer seeds per flower head. We discuss the reliability of environmental clues for plasticity to be adaptive. Further research in the study species should include other plant traits involved in functional responses to drought or potentially associated with invasiveness. [ABSTRACT FROM AUTHOR]