Intercambio gaseoso en dos especies de plantas alto andinas de Chile central: efecto de la asociación a plantas en cojín [Gas exchange in two high andean plant species of central Chile: effect of the association with cushion plants]

Ecologia Austral 06/2005; 15(1):49-58.
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It has been proposed that on stressful environments as high mountain habitats, interactions between species of plants would tend to be of the positive type, increasing in intensity and frequency when resources in the environment become more limited. In this work, we studied the microclimatic modifications produced by cushions of Laretia acaulis species and its effects on the physiological performance of two associated species of the high mountain community located at 2800 m.a.s.l. in Los Andes of central Chile: Taraxacum officinale and Euphorbia collina, which frequently grow within and outside the cushions respectively. Gas exchange measures were taken in order to assess the effects caused by the microclimatic modifications done by cushions plants. We demonstrated that individuals of T. officinale that grow within cushions displayed, unlike their co-specifics in open spaces, a greater net photosynthesis rate. E. collina did not show differences in the rate of net photosynthesis between individuals present within and outside cushions. Only T. officinale displayed a greater rate of photosynthesis in the microsite where it is frequently distributed (within cushions). The effect of association with a nurse (e.g. cushion plants) for large biomass species, such as E. collina, could be less beneficial due to the competition for resources and space; this would explain why E. collina is more frequently found in open spaces.

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Available from: Ernesto Iván Badano, Feb 03, 2014
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    • "Facilitation between plants is a non-consumptive interaction that benefits at least one of the participants (for review, see Callaway 1995). Facilitation is regarded as important in structuring plant communities, particularly in harsh environments such as deserts (Franco and Nobel 1988, Valiente- Banuet et al. 1991, Tirado and Pugnaire 2003), salt-marshes (Hacker and Bertness 1995, Callaway and Pennings 2000), rocky intertidal zones (Molina-Montenegro et al. 2005) and high-mountain ecosystems (Callaway et al. 2002). The most commonly reported facilitative interaction among plants is the " nurse effect, " where a species (the nurse) interacts with the environment to create more favourable micro-habitats than its surroundings for germination, establishment and survival of other plants (Valiente-Banuet et al. 1991, Suzán et al. 1996, Haase et al. 1996, 1997, Tewksbury and Lloyd 2001, Molina-Montenegro et al. 2005a). "
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    ABSTRACT: Facilitation by nurse plants is one of the most commonly reported interactions between plants and is regarded as an important factor in structuring plant communities. We used a meta-analysis to examine the generality of these effects, focusing on cushion plants, a common life-form occurring in high-Andean ecosystems. We targeted the following questions: (1) is there a generalized positive effect of cushions on other vascular plant species along the Andes? (2) do different species groups (i.e., annuals and perennials, natives and exotics) display different association responses to cushions? (3) does the nurse effect of cushions increase with environmental severity? Results indicated that the overall effect of cushions is positive, however these positive effects were more significant amongst exotic plants than in native plants; effects were only positive for perennial plants, and were notably negative for annuals. The positive effects of cushions also increased with physical stress, but only for perennial plants. These results allow us to suggest that as a whole cushions may be acting as keystone species that maintain the structure and diversity of high-Andean plant communities. Nevertheless, since cushions also positively affect the performance of exotic plants, we should be aware of their potential role in promoting biological invasions.
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    ABSTRACT: Positive interactions among native plant species are common in alpine habitats, particularly those where one species (nurse plant) generates microclimatic conditions that are more benign than the surrounding environment, facilitating the establishment of other species. Nonetheless, these microclimatic conditions could facilitate the establishment of non-native species as well. A conspicuous component of the alien alpine flora of the central Chilean Andes is the perennial herb Taraxacum officinale agg. (dandelion). In contrast to other alien species that are restricted to human-disturbed sites, T. officinale is frequently observed growing within native plant communities dominated by cushion plants. In this study we evaluated if T. officinale is positively associated with the cushion plant Azorella monantha. Via seedling survival experiments and gas-exchange measurements we also assessed the patterns of facilitation between cushions and dandelions, and explore the potential mechanisms of invasion by dandelions. T. officinale grows spatially positively associated with cushions of A. monantha. Survival of seedlings, as well as their net-photosynthetic rates and stomatal conductance, were higher within cushions than in open areas away from them, suggesting that the microclimatic modifications generated by this native cushion facilitates the establishment and performance of a non-native invasive species. Our results, as well as other recent studies, highlight the role of native communities in facilitating rather than constraining non-native plant invasions, particularly in stressful habitats such as alpine environments.
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