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Over the past three decades conceptual ecological models, that previously focused on competition, have integrated the pervasive role of positive interactions in community and ecosystem organization. This integration returns us to the seminal insights of some of the founders of ecological and evolutionary thought, including Humbolt, Clements, and Odum. Recognition of the role of positive interactions in nature has dramatically affected our understanding of organic evolution and all levels of ecological organization. Further incorporation of positive interactions into evolutionary ecology will be necessary to successfully address the existential problems of the Anthropocene. Facilitative interactions play crucial roles in community organization, and the stress gradient hypothesis (SGH) provides a simple conceptual framework for the context-dependency of competitive and facilitative interactions. The idea is that positive interactions are more common under high physical and consumer stress, where species benefit from stress-tolerant neighbors, than in benign environments. We explore insights from the SGH into ecological generality, niche theory, community assembly, and diversity effects on ecosystem function and discuss how the SGH can inform our understanding of rapid evolution, mutualisms, exotic invasions, and facilitation cascades. We suggest that, with escalating global stresses, the SGH may provide a conceptual template for an interdependent perspective in ecology that can contribute to conservation and restoration efforts. [ABSTRACT FROM AUTHOR]

Alpine habitats are regarded as particularly vulnerable to the effects of climate change. On one hand, global warming is supposed to contributes to alpine environments becoming less stressful. On the other hand, altered snowpack due to warmer temperatures can intensify the stress in these habitats. The presence of non‐native plants on some of these habitats is due to the facilitative effects exerted by native nurse plants, becoming an additional threat. According to the stress gradient hypothesis the importance of facilitative interactions with nurse species is expected to diminish as environmental harshness decreases due to climate change yet remains important if climate change heightens the stress in alpine habitats. However, the responses also depend on climate change's impact on the nurse species. We conducted an experimental warming experiment in the Andes of the central Chile to assess the effects of warmer temperatures on the growth, reproduction and photochemical efficiency of the cushion nurse plant Azorella madreporica. Further we performed a cushion removal experiment involving three native species (Gamocarpha ventosa, Nocaccea magellanica and Rytidosperma pictum) and two non‐native species (Cerastium arvense and Taraxacum officinale) to assess whether facilitative interactions changed with warming. We expected that under warmer conditions facilitation continued be important for the native species but decreased for the non‐natives as the latter are abundant at warmer low elevations. We found that warmer conditions increased the photochemical efficiency and growth of the nurse cushions. Removal of cushions resulted in high mortality rates for all species. However, under warmer conditions, native species exhibited lower survival rates, whereas non‐natives showed no significant changes compared to control groups. In summary, warmer temperatures were beneficial for the nurses maintaining the importance of facilitative interactions for native species, but not for the non‐natives. [ABSTRACT FROM AUTHOR]

One of the most studied emergent functions of plant community diversity is the resistance of diverse communities to non‐native invasions. As emphasized in this Special Feature, facilitation among native species is a key mechanism by which biodiversity increases various functions, including resistance to invasion. However, when diverse assemblages facilitate non‐native species, diversity–invasibility resistance may be compromised.Here, I review the scientific literature on plant invasion in which facilitative interactions, either among native and non‐native plant species or among non‐native species, affect community invasibility.Native species can directly facilitate non‐native species, and also generate net indirect facilitative effects through suppressing species that compete with non‐native invaders, but examples of the latter are not common. Such direct and indirect facilitation among non‐native species contributes to 'invasional meltdown' that restructures native communities.In general, facilitative interactions between native and non‐native species increased with environmental stress, suggesting that community diversity might resist invasion more effectively in environmentally favourable sites, whereas in environmentally severe sites, facilitative interactions may contribute to invasibility.Synthesis. Native and non‐native species can facilitate each other in direct and indirect ways, with important consequences for the invasibility of communities. Facilitative interactions may alter the fundamental relationship between diversity and invasibility, particularly in environmentally severe habitats. [ABSTRACT FROM AUTHOR]

The effects of many invasive species on invaded communities are still scarcely known. Centaurea solstitialis is an invasive Eurasian herb, widely distributed around the world, but its effects on recipient communities are not well known. To evaluate the effect of C. solstitialis invasion on richness and cover of native and exotic resident species in naturally established communities. We repeated a field experiment in three old-fields of central Chile where C. solstitialis was not present. The experiment simulated the invasion of C. solstitialis by adding 600 seeds per plots of 1 × 1 m in size and compared the richness and cover of all naturally growing species in plots with and without C. solstitialis. For exotics, initial species richness (average ca.18% and 20% per site), and cover (average ca. 20% and 34% per site) were significantly reduced by C. solstitialis in two out of the three sites. The abundances of four out of 17 exotic resident species were negatively affected by C. solstitialis. Native species were not affected by C. solstitialis. C. solstitialis can outcompete resident species of communities where it invades, but local ecological factors influence its effects producing different impacts among species and localities. [ABSTRACT FROM AUTHOR]

Global change is a multifaceted, unprecedented crisis hitting the life support system of our planet. Among global changes, climate change is regarded as one of the most grave threats to biodiversity because of its direct impacts on species and ecosystems integrity and because of its indirect consequences through synergistic effects with other global change factors such as biological invasions. The challenges presented to either reduce or mitigate this biodiversity crisis derived from climate change require novel synthesis and innovation in ecological and evolutionary theory. Positive species interactions within and between trophic levels can play a key role in the resilience of ecological communities. Depending on the tolerance of nurse species to different aspects of climate change, communities can be more or less resilient to those changes. This knowledge has important implications for both natural communities and agroecosystems. Further, our fundamental understanding of the role of positive interactions can also enable both effective conservation and restoration levers in space and time. This special issue includes studies addressing the role of facilitative interactions on the response of ecological systems to climate change. Key concepts examined included stress, gradients, nurse species, spatial scale, translocation, phylogenetics alongside physiochemicals, and variation in the capacity of species to buffer changes. Alpine, tundra, drylands and temperate forests were directly tested, but salient principles were relevant to all ecosystems including a contribution on soil biota and also a call to more open data and collaborative science. Together, this corpus of work highlighted the significance of facilitative interactions in mitigating many of the effects of climate change on biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Niche properties, such as breadth and position along environmental gradients, are hypothesized to determine plant responses to climate change. We explored the properties of different plant niches in a biodiversity hotspot, over a wide span of elevational and latitudinal ranges, to assess the relationship between niche characteristics and the modelled distributional shifts due to climate change. Location: South American temperate forests. Methods: We assessed the niche breadth and position of 118 plant species of South American temperate forests, using an Outlying Mean Index (OMI). Bioclimatic information was gathered for each species from WorldClim, and both present and future distributions were modelled using BIOMOD, considering migration constraints with MIGCLIM. The relationships between niche properties and shifts in elevational and latitudinal distributions were explored using linear regressions. Results: Niche differences among species were related to two bioclimatic dimensions: the first one correlated with the mean diurnal temperature range and precipitation seasonality following the mediterranean—temperate—sub‐Antarctic climatic gradient; the second one correlated with minimum winter temperature along a gradient from oceanic‐influenced habitats to cold tree line habitats. The projected elevational shifts were inversely related to niche breadth and the forecast latitudinal shifts were directly related to niche breadth. The shifts in elevation and latitude for understorey plants were not consistent with the shifts of dominant trees. Main conclusions: The plant niches were successfully discerned by OMI analyses and they were associated with specific morphological or physiological traits. South American temperate forest plants showed an inverse relationship between niche breadth and elevational shifts, but a positive relationship regarding expected latitudinal shifts. This may be related to the fact that niche drivers followed a latitudinal orientation and the species showed the Rapoport's effect. Thus, the niche breadth and latitudinal position of the species should be considered in climatic change studies. [ABSTRACT FROM AUTHOR]

Summary: The Antarctic Peninsula has experienced a rapid warming in the last decades. Although recent climatic evidence supports a new tendency towards stabilization of temperatures, the impacts on the biosphere, and specifically on Antarctic plant species, remain unclear. We evaluated the in situ warming effects on photosynthesis, including the underlying diffusive, biochemical and anatomical determinants, and the relative growth of two Antarctic vascular species, Colobanthus quitensis and Deschampsia antarctica, using open top chambers (OTCs) and gas exchange measurements in the field. In C. quitensis, the photosynthetic response to warming relied on specific adjustments in the anatomical determinants of the leaf CO2 transfer, which enhanced mesophyll conductance and photosynthetic assimilation, thereby promoting higher leaf carbon gain and plant growth. These changes were accompanied by alterations in the leaf chemical composition. By contrast, D. antarctica showed no response to warming, with a lack of significant differences between plants grown inside OTCs and plants grown in the open field. Overall, the present results are the first reporting a contrasting effect of in situ warming on photosynthesis and its underlying determinants, of the two unique Antarctic vascular plant species, which could have direct consequences on their ecological success under future climate conditions. [ABSTRACT FROM AUTHOR]

Abstract: Aims: The sign of interactions among plants in very harsh environments is under debate. The Antarctic tundra is one of the harshest environments on Earth and only two vascular plants (Deschampsia antarctica and Colobanthus quitensis) have successfully established natural populations. D. antarctica mostly establishes facilitative interactions with other species (mosses), but there is no information about the inter‐specific interactions established by C. quitensis. We assessed whether C. quitensis grows frequently associated with D. antarctica, and if D. antarctica neighbours have a positive effect on the survival, growth and photochemical efficiency of C. quitensis individuals. Location: King George Island, Antarctic Peninsula. Methods: To assess the spatial association among the two Antarctic vascular plants fifty 50 m × 50 cm quadrats were sampled on each of four different substrates: moss carpet areas; dead moss carpet areas dominated by D. antarctica; a transition zone between dead moss carpets and fellfields; and fellfields characterized by very poor vegetation cover. Infrared thermal images were taken to estimate whether growth associated with D. antarctica affected the foliar temperature of C. quitensis. The importance of D. antarctica neighbours on the growth, survival and photochemical efficiency of C. quitensis was evaluated with a neighbour removal experiment. Results: The number of C. quitensis individuals associated with D. antarctica was significantly higher than when growing alone in the moss carpet and the dead moss carpet, while in the transition zone there was a trend in that direction. C. quitensis individuals growing associated with D. antarctica were bigger than those growing alone in these three substrate types. In the fellfield site there were no significant differences, neither in the number nor the size of individuals when growing alone or associated with D. antarctica. Foliar temperature of C. quitensis individuals associated with D. antarctica was slightly (1.1°C) but significantly higher than in those growing alone. The growth, survival and photochemical efficiency of C. quitensis individuals with neighbours were higher than in individuals with neighbours removed. Conclusions: Our results indicate that D. antarctica has a facilitative effect on the growth, survival and photochemical efficiency of C. quitensis. Thus, facilitative interactions are present and are important in one of the harshest environments on Earth, although results from the fellfield site indicate that further research is needed. [ABSTRACT FROM AUTHOR]

Snow cover duration, which depends on winter precipitation and temperature, is decreasing along several alpine areas around the world as a consequence of the global warming and further increases are expected in the future. Thus, alpine species that requires cold stratification to initiate seed germination may be threatened in the future. Here we report the results of an exploratory experimental survey to assess the importance of cold stratification for the seed germination in alpine plant species from the High-Andes of central Chile. In addition, we assessed how this requirement varies with elevation at the community level. Seeds of a total of fifty plant species were collected along an altitudinal range from 2200 to 3600 m a.s.l. Eighteen species corresponded to the Low-Andean vegetation belt, while thirteen and nineteen species corresponded to the Mid- and High-Andean vegetation belts, respectively. For each species, seeds that experienced cold-stratification at 4 °C for 3 months and control seeds (stored at room temperature and dry conditions for 3 months) were placed on moist paper in 4 Petri dishes containing 50 seeds each, and arranged in a growth chamber set at 20 °C/10 °C and a photoperiod of 14/10 h. While 36% of the studied species were able to germinate without cold-stratification, after this pre-treatment 74% of these species germinated, suggesting that in general cold-stratification promotes seed germination of these alpine plant species. This positive effect was particularly evident on the species from the lower elevations. At highest elevation both the number of species that showed seed germination and the percentage and velocity of seed germination were low. Nonetheless, non-germinated seeds remained viable, suggesting a deeper dormancy. Our results suggest that cold stratification could be an important requirement for successful seed germination in species from lower elevations, while species from higher elevations could require other factors than cold-stratification to break seed dormancy. Nonetheless, as we did not use temperatures as those experienced in the field, further studies are needed to gain insights into the importance of the duration of cold stratification and the underlying mechanisms involved in the seed germination in the field of high-Andean plant species. [ABSTRACT FROM AUTHOR]

The elevational range of the alpine cushion plant Laretia acaulis (Apiaceae) comprises a cold upper extreme and a dry lower extreme. For this species, we predict reduced growth and increased non-structural carbohydrate (NSC) concentrations (i.e. carbon sink limitation) at both elevational extremes. In a facilitative interaction, these cushions harbor other plant species (beneficiaries). Such interactions appear to reduce reproduction in other cushion species, but not in L. acaulis. However, vegetative effects may be more important in this long-lived species and may be stronger under marginal conditions. We studied growth and NSC concentrations in leaves and stems of L. acaulis collected from cushions along its full elevational range in the Andes of Central Chile. NSC concentrations were lowest and cushions were smaller and much less abundant at the highest elevation. At the lowest elevation, NSC concentrations and cushion sizes were similar to those of intermediate elevations but cushions were somewhat less abundant. NSC concentrations and growth did not change with beneficiary cover at any elevation. Lower NSC concentrations at the upper extreme contradict the sink-limitation hypothesis and may indicate that a lack of warmth is not limiting growth at high-elevation. At the lower extreme, carbon gain and growth do not appear more limiting than at intermediate elevations. The lower population density at both extremes suggests that the regeneration niche exerts important limitations to this species' distribution. The lack of an effect of beneficiaries on reproduction and vegetative performance suggests that the interaction between L. acaulis and its beneficiaries is probably commensalistic. [ABSTRACT FROM AUTHOR]

Positive interactions have started to gain a place as important drivers of community structure and biological diversity. Defined as non-trophic interspecific interactions that increase the average individual fitness of one species, by definition, the presence of one plant species enhances the chances that another species co-occur in the same place, indicating that positive interactions may determine biological diversity. However, this has been poorly explored., The majority of the studies addressing community-level consequences of facilitation have compared the diversity of the plant assemblages growing within nurses vs. those growing outside them, reporting contrasting results among them. Nonetheless, nurses and their alternative microhabitats (open areas among nurses) are part of the same community. Thus, if nurses allow for the persistence of species that otherwise would be excluded from the community, a net increase in the species diversity at the entire community level will be generated even though nurse plants contained fewer species than open areas., Here, we conducted a bibliographic search using the ISI Web of Knowledge data base and reviewed the literature conducted on alpine plant communities where assessments of the diversity of plants growing within and outside a nurse species were available. In most cases nurse species substantially increased species richness at the community level, despite the fact that in some cases, they contained lower species numbers than open areas. Nurse species enhanced species richness more in systems with impoverished local diversity, suggesting that facilitative interactions in alpine habitats act as an insurance policy that sustains diversity under very harsh conditions. [ABSTRACT FROM AUTHOR]

Plant chemical defenses can be qualitative (toxins) to face generalist herbivores and quantitative (digestibility reducers) to specialists. Trichomes can produce chemicals, but also acts as a quantitative defense and in water loss. The shifting defense hypothesis (SDH) poses that invasive plants reduce the production of qualitative defenses against specialist herbivores because those are frequently absent in invaded regions, while increasing defenses against generalist herbivores. Chemical and physical leaf surface defensive traits could give information about direct plant–herbivore interaction in native and non-native regions. We studied leaf surface morphology and epicuticular chemistry of the invasive C. solstitialis in plants from native and non-native regions. Across regions, the main chemical components were sesquiterpene lactones, similar densities of sessile glandular trichomes and a variable number of large multicellular trichomes. Exotic plants face different sets of challenges in the new regions. In accordance with SDH, plants from non-native regions presented higher total sesquiterpene lactones concentrations (qualitative defense). Trichome density was possibly associated to differences in local climatic conditions. Sesquiterpene lactones are likely to play an important role on the invasion success of Centaurea . Leaf surface components provide meaningful information that should be consider in future studies to unravel the mechanisms involved in plant invasions. [ABSTRACT FROM AUTHOR]

In order to assess the effects of climate change in temperate rainforest plants in southern South America in terms of habitat size, representation in protected areas, considering also if the expected impacts are similar for dominant trees and understory plant species, we used niche modeling constrained by species migration on 118 plant species, considering two groups of dominant trees and two groups of understory ferns. Representation in protected areas included Chilean national protected areas, private protected areas, and priority areas planned for future reserves, with two thresholds for minimum representation at the country level: 10% and 17%. With a 10% representation threshold, national protected areas currently represent only 50% of the assessed species. Private reserves are important since they increase up to 66% the species representation level. Besides, 97% of the evaluated species may achieve the minimum representation target only if the proposed priority areas were included. With the climate change scenario representation levels slightly increase to 53%, 69%, and 99%, respectively, to the categories previously mentioned. Thus, the current location of all the representation categories is useful for overcoming climate change by 2050. Climate change impacts on habitat size and representation of dominant trees in protected areas are not applicable to understory plants, highlighting the importance of assessing these effects with a larger number of species. Although climate change will modify the habitat size of plant species in South American temperate rainforests, it will have no significant impact in terms of the number of species adequately represented in Chile, where the implementation of the proposed reserves is vital to accomplish the present and future minimum representation. Our results also show the importance of using migration dispersal constraints to develop more realistic future habitat maps from climate change predictions. [ABSTRACT FROM AUTHOR]

Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a 'safety net' sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change. [ABSTRACT FROM AUTHOR]

Pinus contorta is considered one of the most invasive tree species worldwide, generating significant impacts on biodiversity and ecosystems. In several Patagonian ecosystems in southern Chile, it has escaped from plantations established mainly in the 1970s, and is now invading both forests and treeless environments. In this study, we evaluated the impact of the invasion of P. contorta on microenvironmental conditions in Araucaria araucana forest and Patagonian steppe ecosystems, and assessed how these changes related to the richness and abundance of native and non-native plant species. In each ecosystem, 24 plots of 100 m2 were established along a gradient of P. contorta biomass, where 18 environmental variables and the composition of native and non-native vegetation were measured at a local scale. Our results indicated that increased pine biomass was associated with differences in microclimatic conditions (soil and air temperature, photosynthetically active radiation (PAR), and soil moisture) and soil properties (potassium, nitrate, pH, and litter accumulation). These changes were ecosystem dependent, however, as well as associated with the level of invasion. Finally, the reduction in the richness and abundance of native plants was associated with the changes in soil properties (accumulation of leaf litter, pH, and organic matter) as well as in the microclimate (minimum air temperature, PAR) generated by the invasion of P. contorta. Overall, our results confirm that the invasion of P. contorta impacts microenvironmental conditions (i.e., canopy cover, litter accumulation, minimum air temperature, and maximum soil temperature) and reduces native plant diversity. For future restoration plans, more emphasis should be given to how environmental changes can influence the recovery of invaded ecosystems even after the removal of the living pine biomass (i.e., legacy of the invasion). [ABSTRACT FROM AUTHOR]

Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats. [ABSTRACT FROM AUTHOR]

Abstract: In high-elevation habitats, an apparent trade-off between high growth-rates and freezing resistance has led some authors to assume that seedlings are less freezing resistant than adults. However, because seedlings are exposed to lower and longer freezing events near the ground, they could be more freezing-resistant than adults. As freezing resistance is related to plant height, ontogenetic changes in the intensity of freezing resistance and the mechanism involved should differ between seedlings and adults of tall vs. short plants, with those changes being greater for tall plants. We evaluated differences between seedlings and adult plants in the ability to resist freezing temperatures in 13 high-Andean species from central Chile. In a field laboratory, we determined the low temperature damage, ice nucleation temperature and freezing resistance mechanisms in their leaves. Seedlings were on average 3.4K less freezing resistant than adults with greater differences found for tall plant species. Six species changed their freezing resistance mechanism with ontogeny, including short and tall plants, although changes were greater for tall plant species. Ontogenetic changes in the freezing resistance of high-Andean species seem to be more related to a trade-off between plant-growth and stress resistance than to differences in thermal microhabitats between seedlings and adults. [Copyright &y& Elsevier]

Abstract: Most of the studies that have evaluated the interplay between interference and facilitation have been done at the interspecific level, whereas studies at the intraspecific level are scarce. The montane sclerophyllous forests of central Chile are dominated by the tree Kageneckia angustifolia, a semi-deciduous species that lose part of its foliage during summer. It has been reported that during winter snow accumulates in lower amounts beneath the canopy of K. angustifolia favoring the recruitment of new individuals compared to open areas (i.e., facilitation effect). However, it has also been reported that the leaf litter accumulated beneath parental trees contains allelopathic compounds that decrease seed germination, suggesting that recruitment beneath parental plants can be disfavored (i.e., interference effect). Hence, this system seems appropriate to assess the net-outcome between facilitative and negative effects during the emergence and survival of seedlings during the first year. In this study, we asked (i) what is the net-outcome between facilitative and interfering effects for K. angustifolia? (ii) does this net-outcome varies with the distance to parental trees? (iii) are positive and negative effects consistent through the seedling emergence and first year seedling survival phases? (iv) what are the main mechanisms behind the observed net-outcome? and (v) which is the optimal microhabitat for successful recruitment of this species? In an experimental plot of 10,000m2, we selected ten K. angustifolia trees and evaluated the effect of leaf litter on the emergence and survival of seedlings produced by experimentally sown seed seeds in three different microhabitats: beneath adult trees, edge of canopy and in open areas. In addition, we sampled three K. angustifolia stands to evaluate the microhabitat where the natural recruitment of this species actually occurring. Results showed that (1) seedling emergence was greater beneath canopy, intermediate in canopy edge and low in open areas, (2) whilst leaf litter significantly reduced seed germination, the magnitude of this negative effect was lower than the positive effect of beneath canopy microhabitat, (3) seedling survival was affected by microhabitats but not by the presence of leaf litter, (4) that the main mechanisms behind the observed patterns are the lower and delayed emergence of seedlings in open areas due to the longer duration of snow cover, decreasing the time to growth before the onset of summer drought, and (5) the greatest natural recruitment of K. angustifolia seedlings occurs beneath parental plants. Therefore, our findings suggest that the net-outcome between facilitative and interfering effect during the first year is mostly facilitative, indicating that adult trees of K. angustifolia are exerting a conspecific nurse effect on the recruitment of new individuals, a form of parental care in plants. [Copyright &y& Elsevier]

Abstract: The level and mechanism of resistance to damage from freezing temperatures is related to the ambient temperatures experienced by plants. High-elevation habitats exhibit a thermal gradient in the air–soil profile, exposing ground-level species to more rigorous thermal microhabitats than well aboveground species. Such gradients could explain an inverse relationship between freezing temperature damage (LT50) and plant height, such that leaves of smaller plants tolerate freezing conditions, while leaves of taller plants avoid them. However, microclimatic data have not been included in previous studies evaluating those patterns. On the other hand, a proposed trade-off between plant functional traits and freezing resistance suggest that leaves of growth-forms with higher intensity of growth are less freezing resistant than those with lower growth intensity. In this work, we determined whether the ability to resist freezing temperatures is related to plant height or growth-form in 37 high-elevation species from the Central Chilean Andes. We proposed that (1) plants with contrasting heights are exposed to different thermal conditions during freezing events, (2) the level and the mechanism of freezing resistance are inversely related to plant height, and that (3) the level of freezing resistance varied between plants with low- and high-growth intensities. We found that high-Andean species of different heights are exposed to different thermal conditions depending on the distance from the ground. However, neither level nor mechanisms of freezing resistance were related to plant height. Leaves of both short and tall plants showed similar LT50 and their main freezing resistance mechanism was tolerance. Moreover, leaves of growth-forms with high- and low-growth intensity resisted similar freezing temperatures. Our results are discussed in relation to environmental conditions that characterize the Central Chilean Andes. [Copyright &y& Elsevier]

Alpine habitats have been proposed as particularly sensitive to climate change. Shorter snow cover could expose high-elevation plants to very low temperatures, increasing their risk of suffering damage by freezing, hence decreasing their population viability. In addition, a longer and warmer growing season could affect the hardening process on these species. Thus, understanding the ability of these species to withstand freezing events under warmer conditions is essential for predicting how alpine species may respond to future climate changes. Here we assessed the freezing resistance of 11 species from the central Chilean Andes by determining their low temperature damage (LT50) and freezing point (FP) after experimental warming in the field. Plants were exposed during two growing seasons to a passive increase in the air temperature using open top chambers (OTCs). OTCs increased by ca. 3 K the mean air and soil daytime temperatures, but had smaller effects on freezing temperatures. Leaf temperature of the different species was on average 5.5 K warmer inside OTCs at midday. While LT50 of control plants ranged from −9.9 to −22.4, that of warmed plants ranged from −7.4 to −17.3°C. Overall, high-Andean species growing inside OTCs increased their LT50 ca. 4 K, indicating that warming decreased their ability to survive severe freezing events. Moreover, plants inside OTCs increased the FP ca. 2 K in some studied species, indicating that warming altered processes of ice crystal formation. Resistance of very low temperatures is a key feature of high-elevation species; our results suggest that current climate warming trends will seriously threaten the survival of high-elevation plants by decreasing their ability to withstand severe freezing events. [ABSTRACT FROM AUTHOR]

The reduction of photosynthetic rates with tree age has been proposed as a major driver of the productivity declination along ontogeny. It is not clear, however, how environmental humidity affects stomatal conductance and biochemical potential of photosynthesis in trees belonging to different age-classes. We assessed daily cycles of gas exchange on leaves of juvenile and mature individuals of the tropical high-elevation tree Alnus jorullensis Kunth (Betulaceae), at two sites with contrasting precipitation in the Venezuelan Andes. Photosynthesis and stomatal conductance were higher in juvenile trees during the morning and at noon in the mesic site, and were in general similar between age-classes in the wet site. Under light-saturating conditions, the net photosynthetic rate was similar between the age-classes at the wet site and higher for juvenile trees at the mesic site, whereas stomatal conductance did not differ between age-classes and was higher at the wet site. Daily cycles of gas exchange and a type II regression model between photosynthesis and intercellular CO2 concentration indicated that the better performance of juvenile trees at the mesic site was due to lower non-stomatal limitations. These results support the proposal that non-stomatal limitations—rather than stomatal ones—are involved in the decay of photosynthesis in mature trees, and suggest that such limitations may be evident only under drier conditions. [ABSTRACT FROM AUTHOR]

1. Although the consequences of facilitation at individual and population levels are well known, the community-level consequences of these processes have received much less attention. In particular, the importance of facilitation in determining richness at the entire community level has seldom been evaluated. 2. In this study, we sampled 11 alpine plant communities along the southern Andes in South America, spanning from tropical (25°S) to sub-antarctic latitudes (55°S). Plant communities were dominated by cushion plants, a particular growth form that acts as a nurse plant for other plant species. Through rarefaction curves, we assessed the effectiveness of community sampling and estimated the number of species present within and outside cushions. Non-metric Multidimensional Scaling ordinations (NMDS) were used to assess differences between the species assemblages growing within and outside cushions. Finally, samples from cushions and open areas were combined in a single matrix accounting for the difference in cover between both microhabitats, and through rarefaction curves we assessed how many more species are added to the community due to the presence of cushions. 3. Samples taken within cushions always contained more species than equivalent samples from open areas. However, the magnitude of this difference varied among communities. NMDS ordination indicated that cushions generate species assemblages structurally different from those found in open areas. Inclusion of samples from cushion and open areas in synthetic analyses – where differences in cover were accounted for – indicated that the presence of cushions consistently increased species richness at the entire community level. The magnitude of these increases in species richness varied with habitat severity, with lower values at both extremes of the environmental severity gradient. 4. Synthesis. Facilitative interactions with cushion nurse plants along the high Andes of southern South America changed plant assemblage structure and increased species richness at the entire community level, indicating that facilitative interactions are pivotal in maintaining the diversity of these harsh environments. [ABSTRACT FROM AUTHOR]

• Predicted increases in the length of the growing season as a result of climate change may more frequently expose high-elevation plants to severe frosts. Understanding the ability of these species to resist frosts during the growing season is essential for predicting how species may respond to changes in temperature regimes. • Here, we assessed the freezing resistance of 24 species from the central Chilean Andes by determining their low temperature damage (LT50), ice nucleation temperature (NT), freezing point (FP) and freezing resistance mechanism (i.e. avoidance or tolerance). • The Andean species were found to resist frosts from −8.2 to −19.5°C during the growing season, and freezing tolerance was the most common resistance mechanism. Freezing resistance (LT50) varied within the growing season, decreasing towards the end of this period in most of the studied species. However, the FP showed the opposite trend. LT50 increased with elevation, whilst FP was lower in plants from lower elevations, especially late in the growing season. • Andean species have the potential to withstand severe freezing conditions during the growing season, and the aridity of this high-elevation environment seems to play an important role in determining this high freezing resistance. [ABSTRACT FROM AUTHOR]

Abstract: We studied the effect of heat shock and wood-fueled smoke on the emergence of native and exotic plant species in soil samples obtained in an evergreen shrubland of central Chile, located on the eastern foothills of the Coastal Range of Lampa. Immediately after collection samples were dried and stored under laboratory condition. For each two transect, 10 samples were randomly chosen, and one of the following treatments was applied: 1) Heat-shock treatment. 2) Plant-produced smoke treatment. 3) Combined heat-and-smoke treatment. 4) Control, corresponding to samples not subjected to treatment. Twenty-three species, representing 12 families, emerged from the soil samples. The best-represented families were Poaceae and Asteraceae. All of the emerged species were herbs, 21 were annuals, and 14 were exotic to Chile. Fire-related triggers used in this study did not increase the emergence and/or abundance of exotic species with respect to natives in soil samples. Interestingly, this study provides evidence that heat-shock can increase the emergence of native herbs. [Copyright &y& Elsevier]

1. Alien invasive plants possessing attractive flowers can affect the interactions between native plants and their pollinators. The few studies conducted so far have reported positive, negative and neutral effects of the presence of an invasive species on the pollinator visitation rates and seed output of native species. However, the role played by the density of the alien species has been seldom explored. 2. While high densities of the invasive species can negatively effect the pollinator visitation rates and seed output of the native species, due to sequestration of pollinators by the invasive species, at lower densities the invasive can attract pollinators that otherwise would not visit patches of native species, positively affecting their reproduction. 3. Using observations and pollinator exclusions at a site at 2800 m altitude in the central Chilean Andes, we show that the alien herb Taraxacum officinale (Asteraceae), possessing showy floral capitula, shares pollinators to a high degree (> 90%) with two co-occurring native Asteraceae: Hypochaeris thrincioides and Perezia carthamoides. Pollinator exclusion indicated that both natives are highly dependent on insect visitation to produce seeds. 4. Using manipulative supplemental hand-pollination and experiments, where we varied the density of T. officinale, we determined that seed output in H. thrincioides and P. carthamoides is pollen-limited and that its magnitude is not affected by the presence of the exotic. Further, while the presence of one individual of T. officinale around focal native individuals showed neutral or facilitative effects on pollinator service or seed output in the two native species, the presence of five individuals of T. officinale negatively affected these reproductive variables. 5. Synthesis. Our results suggest that the effects of the presence of alien invasive plant species with attractive flowers vary with their density. This demonstrates the need to experimentally test for the potential impacts of introduced species at different densities before prematurely coming to conclusions regarding their assumed negative or positive effects in native ecosystems. [ABSTRACT FROM AUTHOR]

Ecosystem engineers are organisms able to modulate environmental forces and, hence, may change the habitat conditions for other species. In so doing, ecosystem engineers may affect both species richness and evenness of communities and, in consequence, change species diversity. If these changes in community attributes are related to the magnitude of the habitat changes induced by the engineers, it seems likely that engineer species will have greater effects on diversity in sites where they cause larger habitat changes. We addressed this issue by evaluating the effects of three alpine cushion plants on species richness, evenness, and diversity of high-Andean plant communities. Given that the difference in microclimatic conditions between cushions and the external environment increases with elevation, we proposed that these organisms should have greater effects on community attributes at higher than at lower elevation sites. Results showed that the three cushion species had positive effects on species richness, diversity, and evenness of plant communities. It was also observed that the magnitude of these effects changed with elevation: positive effects on species richness and diversity increased towards upper sites for the three cushions species, whereas positive effects on evenness increased with elevation for one cushion species but decreased with elevation for other two cushion species. These results suggest that the presence of cushions is important to maintain plant diversity in high-Andean communities, but this positive effect on diversity seems to increase as the difference in environmental conditions between cushions and the external environment increases with elevation. [ABSTRACT FROM AUTHOR]

Aim To integrate the effects of ecosystem engineers (organisms that create, maintain or destroy habitat for other species) sharing the same archetype on species diversity, and assess whether different engineer species have generalized or idiosyncratic effects across environmentally similar ecosystems. Location High-Andean habitats of Chile and Argentina, from 23° S to 41° S. Methods We measured and compared the effects of eight alpine plants with cushion growth-form on species richness, species diversity (measured as the Shannon–Wiener index) and evenness of vascular plant assemblages across four high-Andean ecosystems of Chile and Argentina. Results The presence of cushion plants always increased the species richness, diversity (measured as the Shannon–Wiener index) and evenness of high-Andean plant assemblages. However, while the presence of different cushion species within the same ecosystem controlled species diversity in the same way, these effects varied between cushion species from different ecosystems. Main conclusions Results consistently supported the idea that increases in habitat complexity due to the presence of ecosystem engineers, in this case cushion plants, would lead to higher community diversity. Results also indicate that effects of the presence of different cushion species within the same ecosystem could be generalized, while the effects of cushion species from different ecosystems should be considered idiosyncratic. [ABSTRACT FROM AUTHOR]

• In alpine habitats, positive interactions among plants tend to increase with elevation as a result of altitudinal increase in environmental harshness. However, in mountains located in arid zones, lower elevations are also stressful because of scarce availability of water, suggesting that positive interactions may not necessarily increase with elevation. • Here we analysed the spatial association of plant species with the nurse cushion plant Laretia acaulis at two contrasting elevations, and monitored the survival of seedlings of two species experimentally planted within and outside cushions in the semiarid Andes of central Chile. • Positive spatial associations with cushions were more frequent at lower elevations. Species growing at the two elevations changed the nature of their association with cushions from neutral or negative at higher elevations to positive at lower elevations. Survival of seedlings was higher within cushions, particularly at lower elevations. • The increased facilitation by cushions at lower elevations seems to be related to provision of moisture. This result suggests that cushion plants play a critical role in structuring alpine plant communities at lower elevations, and that climatic changes in rainfall could be very relevant for persistence of plant communities. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

Aim To analyse quantitatively the biogeographical distribution pattern of species of the Cytiseae Bercht. & J. Presl (= Genisteae Benth.) tribe in the Iberian Peninsula and the Balearic islands, and to identify environmental variables related to the distributional patterns. Location Iberian Peninsula and Balearic islands, using the 61 administrative provinces as operational geographical units. Methods in order to identify chorotypes (groups of species with similar geographical distribution), we performed a UPGMA classification based on the similarity index of Baroni-Urbani & Buser. The method of McCoy et al. [Ecology 67 (1986), 749] enabled us to detect the significant groups and to differentiate them from those groupings that could be generated at random. Logistic regression analyses and environmental gradient analyses (DCA and CCA) were performed in order to find the relationships between the environmental variables and the observed distributional patterns. Results Sixteen chorotypes were obtained between the Cytiseae species of the Iberian Peninsula and the Balearic islands. The thermal variables showed the greatest influence in species distribution. Specifically, temperatures (maximum, minimum and mean) of the coldest months were associated with the majority of the chorotypes. Main conclusions The species of the Cytiseae tribe were not randomly distributed in space, and can be classified in groups of species with common distributional patterns. The importance of cold tolerance in the distribution of these species, as well as their preference for acidic soils, was demonstrated. Certain general tendencies seem to exist with respect to the distribution of the biota in the Iberian Peninsula, and these seem to be independent of the taxonomic groups involved and to be determined by convergent macroclimatic factors. [ABSTRACT FROM AUTHOR]

Comparisons between regions with similar climates have traditionally helped to tackle big questions in evolutionary ecology and historical biogeography. We claim that plant invasion ecology can benefit greatly from further and better comparisons at regional and global scales. In this note we discuss the potentials and limitations of comparing climatically analogous regions to provide novel insights into the mechanisms of alien plant invasions. Comparisons among areas with similar climates have the advantage that some features of the abiotic environment are within a narrower range of variation, enabling the researcher to focus on the effects of propagule pressure, microenvironmental differences and, more importantly, the biotic environment in the invasion process. However, there are two major issues that limit the strengths of such comparisons: (1) non-standardized databases of alien species, especially in less developed countries; and (2) deficient sampling designs. We argue that we should take advantage of comparative studies of alien plant invasions across regions with similar climates not only to obtain useful insights about invasions, but to search for generalities beyond invasion ecology that contribute to our knowledge of natural systems. [ABSTRACT FROM AUTHOR]

Abstract. It has been proposed that in the harsh arctic and alpine climate zones, small microtopographic variations that can generate more benign conditions than in the surrounding environment could be perceived as safe sites for seedling recruitment. Cushion plants can modify wind pattern, temperature and water availability. Such modifications imply that cushion plants could act as 'nurse plants' facilitating the recruitment of other species in the community. This effect should be more evident under stressful conditions. We tested these hypotheses comparing the number of species that grow inside and outside Bolax gummifera cushions at two elevations (700 and 900 m a.s.l.) in the Patagonian Andes of Chile (50 °S). At both elevations, and in equivalent areas, the number of species was registered within and outside cushions. A total of 36 and 27 plant species were recorded either within or outside B. gummifera cushions at 700 and 900 m a.s.l., respectively. At 700 m a.s.l., 33 species were recorded growing within cushions and 29 outside them, while at 900 m a.s.l. these numbers were 24 and 13 respectively. At both elevations there were significantly more species growing within than outside cushions, and the proportion of species growing within cushions increased with elevation. Thus there is a nurse effect of cushion plants and it is more evident at higher elevations. Shelter from wind and increased soil water availability seem to be the factors that increase plant recruitment within cushions. [ABSTRACT FROM AUTHOR]

Summary1 It is unclear whether soil seed banks in alpine environments are a result of selection for extended seed dormancy, of ideal conditions for seed preservation in the soil, or a combination of both. 2 The nature of the soil seed bank was investigated in the perennial herb Phacelia secunda (Hydrophyllaceae) through reciprocal burial experiments using seeds obtained from populations growing at 1600, 2200, 2900 and 3400 m a.s.l. in the mediterranean Andes of central Chile. At the four elevations, six replicates of 50 seeds each, from each of the four elevational sources, were buried at 5 cm depth in mesh envelopes, placed in wire cages to protect against predation. Seeds were retrieved 1, 2 and 3 years after burial, and numbers of ungerminated seeds, and of those that remained viable, were determined. 3 At all elevations of seed burial, increasing proportions of seeds remained ungerminated, and proportionately more of the ungerminated seeds remained viable, as elevation of source of seed increased. For seed from low elevation, more seeds remained viable in the soil at the higher burial sites. However, for the seeds from higher elevation sources, seeds remaining viable were similar in number at all sites for seed burial. Half-lives of seed buried at the source elevation, calculated from the log-logistic distribution, increased with elevation, and ranged from 188 days at 1600 m to 354 days at 3400 m. 4 The results suggest that the propensity to form a persistent seed bank in P. secunda increases with elevation. Seeds from the highest elevations had the longest persistence, and this was largely unaffected by soil preservation conditions. Seeds from lower elevations survived for less time, and this was modifiable by preservation conditions. These results suggest that both selective effects and soil conditions may be involved in soil seed bank expression in the alpine environment. [ABSTRACT FROM AUTHOR]

The study of ancient species provides valuable information concerning the evolution of specific adaptations to past and current environmental conditions. Araucaria araucana (Molina) K. Koch belongs to one of the oldest families of conifers in the world, but despite this, there are few studies focused on its physiology and responses to changes in environmental conditions. We used an integrated approach aimed at comprehensively characterizing the ecophysiology of this poorly known species, focusing in its stomatal, mesophyll and biochemical traits, hypothesizing that these traits govern the carbon assimilation of A. araucana under past and present levels of atmospheric CO2. Results indicated that A. araucana presents the typical traits of an ancient species, such as large stomata and low stomatal density, which trigger low stomatal conductance and slow stomatal responsiveness to changing environmental conditions. Interestingly, the quantitative analysis showed that photosynthetic rates were equally limited by both diffusive and biochemical components. The Rubisco catalytic properties proved to have a low Rubisco affinity for CO2 and O2, similar to other ancient species. This affinity for CO2, together with the low carboxylation turnover rate, are responsible for the low Rubisco catalytic efficiency of carboxylation. These traits could be the result of the diverse environmental selective pressures that A. araucana was exposed during its diversification. The increase in measured temperatures induced an increase in stomatal and biochemical limitations, which together with a lower Rubisco affinity for CO2 could explain the low photosynthetic capacity of A. araucana in warmer conditions. [ABSTRACT FROM AUTHOR]

• Andean native species are dependent on pollen transport by insects for seed set. • The invasive Taraxacum officinale co-flowers and shared pollinators with natives. • The overlap in pollinators was not related with flower similarity among species. • Taraxacum officinale might alter the reproduction of native species in the Andes. Non-native plant species with a taxonomic affinity to co-occurring natives may perform best as invaders into plant-pollinator networks because their similarity in floral morphologies with natives enabled them to co-opt their pollinators. However, non-native species may impact the reproduction of natives by altering their pollination only if they share pollinators and if natives depend on pollinators for seed-set, premises that are often assumed but seldom tested. The non-native invasive species Taraxacum officinale (Asteraceae) co-exist and co-flower with other asteraceous species in the high elevation of the central Chilean Andes. In this study we determined the dependence on pollinators for seed-set in five co-occurring and co-flowering native asteraceous species and assessed the similarity in insect pollinators between the non-native and this five native species that differ in their floral similarity with the former species. Pollinator exclusion experiments were performed to determine the dependence of pollinators for seed-set in the native species. Characteristics such as capitula size and colour were measured to quantitatively assess the similarity in the floral morphology between T. officinale and the native species. The identity and visitation rates of insect pollinators that visit T. officinale and the five native species were determined. Native species were highly dependent on the transport of pollen by insects to produce seeds. T. officinale shared a moderate to high proportion (34–94%) of insect pollinators with the five asteraceous native species studied, but the level of overlap in pollinators was not related with the floral similarity between the non-native and the native species. The presence of the non-native species T. officinale has the potential to alter the pollinator services to co-flowering native species in the Andes of central Chile, with no higher impacts on those species with the most similar flowers. [ABSTRACT FROM AUTHOR]

Aims: Changes in precipitation patterns, such as the predicted increases in the frequency of climatic extremes, are likely to alter plant communities, but whether responses to drought or to wetter conditions respectively cause consistent, opposite responses is debated. Here, we assessed the response in biomass production and species diversity of water‐limited plant communities to the direction (increase or decrease) and magnitude (micro‐ and macro‐climatic effects) of changes in soil moisture. Location: We reciprocally translocated soils containing seed banks from two climates (semi‐arid and mediterranean) at a micro‐climatic (opposite slopes) and a macro‐climatic scale (between climates) in Chile. Results: Biomass production for the soils that were translocated from wetter to drier climates was unrelated to the available soil moisture. The lowest biomass was produced in the wettest climate on the wet slope. Biomass production increased after a translocation to the drier climate (representing the largest change in climate). Nonetheless, the highest overall biomass for the wet to dry translocation was produced on the mediterranean dry slope with intermediate soil moisture. However, on the same mediterranean dry slope, biomass was almost zero for soil translocated the other way round (from drier to wetter). Diversity after 24 months was unaffected by micro‐climatic change, but soils transplanted toward the drier climate yielded a plant community with increased diversity. Conclusion: Our results showed direction and magnitude of climate change but also the response factor that is studied matters to detect direction‐dependent responses; i.e., species richness had a linear and reversible response. However, the response of biomass depended on the origin of the transplanted material (soil and plant community), indicating history dependence (hysteresis). This emphasizes that responses to unidirectional climate manipulation experiments may not be able to capture the entire nature of the response of plant communities to climate change. [ABSTRACT FROM AUTHOR]

One of the well-documented effects of regional warming in Antarctica is the impact on flora. Warmer conditions modify several leaf anatomical traits of Antarctic vascular plants, increasing photosynthesis and growth. Given that CO2 and water vapor partially share their diffusion pathways through the leaf, changes in leaf anatomy could also affect the hydraulic traits of Antarctic plants. We evaluated the effects of growth temperature on several anatomical and hydraulic parameters of Antarctic plants and assessed the trait co-variation between these parameters and photosynthetic performance. Warmer conditions promoted an increase in leaf and whole plant hydraulic conductivity, correlating with adjustments in carbon assimilation. These adjustments were consistent with changes in leaf vasculature, where Antarctic species displayed different strategies. At higher temperature, Colobanthus quitensis decreased the number of leaf xylem vessels, but increased their diameter. In contrast, in Deschampsia antarctica the diameter did not change, but the number of vessels increased. Despite this contrasting behavior, some traits such as a small leaf diameter of vessels and a high cell wall rigidity were maintained in both species, suggesting a water-conservation response associated with the ability of Antarctic plants to cope with harsh environments. [ABSTRACT FROM AUTHOR]

It is unclear whether the frequently observed increase in non-structural carbohydrates (NSC) in plants exposed to low temperatures or drought reflects a higher sensitivity of growth than photosynthesis in such conditions (i.e. sink limitation), or a prioritization of carbon (C) allocation to storage. Alpine areas in Mediterranean-type climate regions are characterized by precipitation increases and temperature decreases with elevation. Thus, alpine plants with wide elevational ranges in Mediterranean regions may be good models to examine these alternative hypotheses. We evaluated storage and growth during experimental darkness and re-illumination in individuals of the alpine plant Phacelia secunda from three elevations in the Andes of central Chile. We hypothesized that storage is prioritized regarding growth in plants of both low- and high elevations where drought and cold stress are greatest, respectively. We expected that decreases in NSC concentrations during darkness should be minimal and, more importantly, increases in NSC after re-illumination should be higher than increases in biomass. We found that darkness caused a significant decrease in NSC concentrations of both low- and high-elevation plants, but the magnitude of the decrease was lower in the latter. Re-illumination caused higher increase in NSC concentration than in biomass in both low- and high-elevation plants (1.5- and 1.9-fold, respectively). Our study shows that C allocation in Phacelia secunda reflects ecotypic differences among elevation provenances and suggests that low temperature, but not drought, favours C allocation to storage over growth after severe C limitation. [ABSTRACT FROM AUTHOR]

Environmental conditions can modify the intensity and sign of ecological interactions. The stress gradient hypothesis (SGH) predicts that facilitation becomes more important than competition under stressful conditions. To properly test this hypothesis, it is necessary to account for all (not a subset of) interactions occurring in the communities and consider that species do not interact at random but following a specific pattern. We aim to assess elevational changes in facilitation, in terms of species richness, frequency and intensity of the interaction as a function of the evolutionary relatedness between nurses and their associated species. We sampled nurse and their facilitated plant species in two 1000–2000 m. elevation gradients in Mediterranean Chile where low temperature imposes a mortality filter on seedlings. We first estimated the relative importance of facilitation as a mechanism adding new species to communities distributed along these gradients. We then tested whether the frequency and intensity of facilitation increases with elevation, taking into account the evolutionary relatedness of the nurse species and the facilitated species. We found that nurses increase the species richness of the community by up to 35%. Facilitative interactions are more frequent than competitive interactions (56% versus 44%) and facilitation intensity increased with elevation for interactions involving distantly related lineages. Our results highlight the importance of including an evolutionary dimension in the study of facilitation to have a clearer picture of the mechanisms enabling species to coexist and survive under stressful conditions. This knowledge is especially relevant to conserve vulnerable and threatened communities facing new climate scenarios, such as those located in Mediterranean‐type ecosystems. [ABSTRACT FROM AUTHOR]

Summary: Plant–plant positive interactions are key drivers of community structure. Yet, the underlying molecular mechanisms of facilitation processes remain unexplored. We investigated the 'nursing' effect of Maihueniopsis camachoi, a cactus that thrives in the Atacama Desert between c. 2800 and 3800 m above sea level. We hypothesised that an important protective factor is thermal amelioration of less cold‐tolerant species with a corresponding impact on molecular phenotypes.To test this hypothesis, we compared plant cover and temperatures within the cactus foliage with open areas and modelled the effect of temperatures on plant distribution. We combined eco‐metabolomics and machine learning to test the molecular consequences of this association.Multiple species benefited from the interaction with M. camachoi. A conspicuous example was the extended distribution of Atriplex imbricata to colder elevations in association with M. camachoi (400 m higher as compared to plants in open areas). Metabolomics identified 93 biochemical markers predicting the interaction status of A. imbricata with 79% accuracy, independently of year.These findings place M. camachoi as a key species in Atacama plant communities, driving local biodiversity with an impact on molecular phenotypes of nursed species. Our results support the stress‐gradient hypothesis and provide pioneer insights into the metabolic consequences of facilitation. [ABSTRACT FROM AUTHOR]

Abstract In the Southern Alps, climate warming induced the use of artificial snow since two decades. In this area, two different ski piste management practices prevail: (1) large and medium ski resorts (M), which guarantee a ski season of four to five months using artificial snow, whereas (2) in the small, local ski resorts (S) it usually lasts two or three months. Our research addresses two main questions: 1) what is the impact of the ski pistes on the physico-chemical properties of the snow, on the soil and on the vegetation of mountain grassland ecosystems and 2) does the impact on the mountain grassland ecosystems change between medium and small ski resorts? Our experimental approach follows a pairwise design of plots on mountain grasslands of the ski pistes and control plots on mountain grasslands outside the pistes, where we examined the snow and soil properties and the vegetation composition. Under the long ski-season management (M) we found a significantly lower soil temperature below the snow cover of the ski pistes than the one below the natural snowpack, but this difference was limited to the period of natural snow cover. Only in M, pistes showed a lower biomass production and species richness in the mountain grassland plant communities compared to the controls, while there was no effect in S. The proportions of plant functional groups' cover changed in both ski resort types between piste and control. The most important factors affecting the observed differences in vegetation between pistes and controls were snow duration, snow and soil chemical properties, with more marked differences in the soil properties in M respect to S. The study concludes that reducing the ski season's length, therefore limiting the artificial snow's input, as in S, is more adequate to minimize the environmental impact in a changing climate. Graphical abstract Unlabelled Image Highlights • Soil and snow parameters differed strongly between ski pistes and surroundings. • In absence of natural snow soil freezing was as frequent as under artificial snow. • The share of plant functional groups and plant richness was differentiated. • The impact on vegetation is much stronger in medium compared to small ski areas. [ABSTRACT FROM AUTHOR]

Abstract: Questions: How do phylogenetic and functional trait dispersions respond to multiple abiotic gradients? Are functional trait and phylogenetic dispersions coupled across different spatial scales? Does phylogenetic signal on functional trait data help to elucidate the degree to which phylogenetic information is providing novel information? Location: Three massifs in mediterranean‐type climate zone of the high Andes, central Chile. Methods: We sampled plant species composition in 20 alpine sites above the tree line at three different spatial scales: plot (20 m × 20 m), subplot (2.4 m × 2.4 m) and cell (30 cm × 30 cm). Functional and phylogenetic mean pair‐wise distances (MPD) calculated using data on six functional traits (maximum plant height, plant size, leaf area, specific leaf area, leaf dry matter content and leaf thickness) and a molecular phylogeny (rbcL and matK) were compared to the patterns expected under a null model to characterize the functional and phylogenetic dispersion along interacting elevation and potential solar radiation gradients. Results: Our results show that functional and phylogenetic dispersion were related and influenced by potential solar radiation, but the effect of this factor varied with elevation. Overdispersion was found in the most stressful sites, while clustering was observed where the conditions were milder, suggesting a relevant role of facilitation and competitive interactions, respectively. While Blomberg's K statistic indicated no phylogenetic signal for the studied plant traits, Pagel's λ indicated phylogenetic signal, but not of strong intensity (<1), suggesting that the correlation between the functional and phylogenetic diversities was low and that additional unmeasured traits with phylogenetic signal were likely to be important in determining the structure of the studied communities. Conclusions: Our results support the hypothesis that biotic interactions modulated by environmental conditions are important for alpine plant community assembly. Moreover, they reinforce the notion that multiple processes shape community structure, and this can be elucidated by examining interacting environmental gradients, such as elevation and potential solar radiation, and taking into account multiple spatial scales. Our results reinforce the use of both functional and phylogenetic diversities simultaneously and discourage the use of phylogenetic diversity as a surrogate of functional structure. [ABSTRACT FROM AUTHOR]

Specialization, contextualized in a resource axis of an organism niche, is a core concept in ecology. In biotic interactions, specialization can be determined by the range of interacting partners. Evolutionary and ecological factors, in combination with the surveyed scale (spatial, temporal, biological, and/or taxonomic), influence the conception of specialization. This study aimed to assess the specialization patterns and drivers in the lichen symbiosis, considering the interaction between the principal fungus (mycobiont) and the associated Nostoc (cyanobiont), from a community perspective considering different spatial scales. Thus, we determined Nostoc phylogroup richness and composition of lichen communities in 11 Nothofagus pumilio forests across a wide latitudinal gradient in Chile. To measure specialization, cyanobiont richness, Simpson's and d′ indices were estimated for 37 mycobiont species in these communities. Potential drivers that might shape Nostoc composition and specialization measures along the environmental gradient were analysed. Limitations in lichen distributional ranges due to the availability of their cyanobionts were studied. Turnover patterns of cyanobionts were identified at multiple spatial scales. The results showed that environmental factors shaped the Nostoc composition of these communities, thus limiting cyanobiont availability to establish the symbiotic association. Besides, specialization changed with the spatial scale and with the metric considered. Cyanolichens were more specialized than cephalolichens when considering partner richness and Simpson's index, whereas the d′ index was mostly explained by mycobiont identity. Little evidence of lichen distributional ranges due to the distribution of their cyanobionts was found. Thus, lichens with broad distributional ranges either associated with several cyanobionts or with widely distributed cyanobionts. Comparisons between local and regional scales showed a decreasing degree of specialization at larger scales due to an increase in cyanobiont richness. The results support the context dependency of specialization and how its consideration changes with the metric and the spatial scale considered. Subsequently, we suggest considering the entire community and widening the spatial scale studied as it is crucial to understand factors determining specialization. [ABSTRACT FROM AUTHOR]

The aim was to assess patterns of plant diversity in response to elevation and disturbance in a tropical mountain. The study area was located in north-central portion of the Eastern Cordillera of the Ecuadorian Andes, on a road from 1,150 m a.s.l. (Osayacu) to 4,000 (Papallacta). Along a mountain road spanning a wide altitudinal gradient, at 20 elevations we sampled three plots: one at the roadside and two perpendicular to the roadside. The relationship between elevation and species richness was assessed using linear and quadratic regressions, the effect of disturbance on species richness was determined by ANCOVA and a t test with parameters obtained from quadratic equations. Similarity of species composition among the roadside and sites distant was evaluated with the Chao-Jaccard and classic Jaccard similarity indices, the distribution of non-native species according to their origin were analyzed with linear and quadratic regression. The native species showed a linearly monotonic decrease with elevation, whereas non-natives showed a quadratic distribution. Disturbed areas had the greatest number of non-native species and lower native species richness, showing also a high floristic similarity; less disturbed areas showed the opposite. The non-native species of temperate origin were more numerous and showed unimodal elevational distribution, while species of tropical origin were few and decreased linearly with elevation. We conclude that in a tropical highland mountain range, native and non-native plant species respond differently to elevation: native species exhibit a monotonically linear decrease, and non-native species show a unimodal trend. Disturbance positively affects non-native species showing higher richness and fewer species turnover. In addition, the non-native species are located along of the elevational gradient in relation to their biogeographic origin. [ABSTRACT FROM AUTHOR]

Fire is a selective agent shaping plant traits and community assembly in fire-prone ecosystems. However, in ecosystems with no fire history, it can be a cause of land degradation when it is suddenly introduced by humans, as plant species may not be able to respond to such novel disturbance. Unlike other Mediterranean-type ecosystems (MTE) of the world, natural fires have not been frequent during the Quaternary in the matorral of Central Chile, and thus, plant adaptive responses are expected to be uncommon. We evaluated the effect of heat shock on seed survival and germination of 21 native woody plants of the Chilean matorral and compiled information on smoke-stimulation and resprouting, to evaluate the importance of fire-adaptive responses in the context of the other MTE. We found that in the Chilean woody flora negative seed responses to fire cues were more frequent than positive responses. Although resprouting is a relatively widespread trait, fire-stimulated germination is not as common in the Chilean matorral as in other MTE. The seeds of seven endemic species were strongly damaged by fire cues and this should be considered in post-fire restoration planning. However, our results also showed that many species were resistant to elevated doses of heat shock and in some, germination was even stimulated. Thus, future research should focus on the evolutionary causes of these responses. These findings could help to develop strategies for fire management in the Chilean matorral. In addition, they will improve our understanding of the evolutionary forces that shaped this plant community and to better frame this region among the other MTE worldwide. [ABSTRACT FROM AUTHOR]

Particular physiological traits allow the vascular plants Deschampsia antarctica Desv. and Colobanthus quiten- sis (Kunth) Bartl. to inhabit Antarctica. The photosynthetic performance of these species was evaluated in situ, focusing on diffusive and biochemical constraints to CO2 assimilation. Leaf gas exchange, Chl a fluorescence, leaf ultrastructure, and Rubisco catalytic properties were examined in plants growing on King George and Lagotellerie islands. In spite of the species- and population-specific effects of the measurement temperature on the main photosynthetic parameters, CO2 assimilation was highly limited by CO2 diffusion. In particular, the mesophyll conductance (gm)--estimated from both gas exchange and leaf chlorophyll fluorescence and modeled from leaf anatomy--was remarkably low, restricting CO2 diffusion and imposing the strongest constraint to CO2 acquisition. Rubisco presented a high specificity for CO2 as determined in vitro, suggesting a tight co-ordination between CO2 diffusion and leaf biochemistry that may be critical ultimately to optimize carbon balance in these species. Interestingly, both anatomical and biochemical traits resembled those described in plants from arid environments, providing a new insight into plant functional acclimation to extreme conditions. Understanding what actually limits photosynthesis in these species is important to anticipate their responses to the ongoing and predicted rapid warming in the Antarctic Peninsula. [ABSTRACT FROM AUTHOR]

Roads are known to act as corridors for dispersal of plant species. With their variable microclimate, role as corridors for species movement and reoccurring disturbance events, they show several characteristics that might influence range dynamics of both native and non-native species. Previous research on plant species ranges in mountains however seldom included the effects of roads. To study how ranges of native and non-native species differ between roads and adjacent vegetation, we used a global dataset of plant species composition along mountain roads. We compared average elevation and range width of species, and used generalized linear mixed models (GLMMs) to compile their range optimum and amplitude. We then explored differences between roadside and adjacent plots based on a species' origin (native vs non-native) and nitrogen and temperature affinity. Most non-native species had on average higher elevational ranges and broader amplitudes in roadsides. Higher optima for non-native species were associated with high nitrogen and temperature affinity. While lowland native species showed patterns comparable to those in non-native species, highland native species had significantly lower elevational ranges in roadsides compared to the adjacent vegetation. We conclude that roadsides indeed change the elevational ranges of a variety of species. These changes are not limited to the expansion of non-native species along mountain roads, but also include both upward and downward changes in ranges of native species. Roadsides may thus facilitate upward range shifts, for instance related to climate change, and they could serve as corridors to facilitate migration of alpine species between adjacent high-elevation areas. We recommend including the effects of mountain roads in species distribution models to fine-tune the predictions of range changes in a warming climate. [ABSTRACT FROM AUTHOR]

Invasive species often possess a great capacity to adapt to novel environments in the form of spatial trait variation, as a result of varying selection regimes, genetic drift, or plasticity. We explored the geographic differentiation in several phenotypic traits related to plant growth, reproduction, and defense in the highly invasive Centaurea solstitialis by measuring neutral genetic differentiation (FST), and comparing it with phenotypic differentiation (PST), in a common garden experiment in individuals originating from regions representing the species distribution across five continents. Native plants were more fecund than non‐native plants, but the latter displayed considerably larger seed mass. We found indication of divergent selection for these two reproductive traits but little overall genetic differentiation between native and non‐native ranges. The native versus invasive PST–FST comparisons demonstrated that, in several invasive regions, seed mass had increased proportionally more than the genetic differentiation. Traits displayed different associations with climate variables in different regions. Both capitula numbers and seed mass were associated with winter temperature and precipitation and summer aridity in some regions. Overall, our study suggests that rapid evolution has accompanied invasive success of C. solstitialis and provides new insights into traits and their genetic bases that can contribute to fitness advantages in non‐native populations. [ABSTRACT FROM AUTHOR]

Litter decomposition rates are determined by the interplay of climate, decomposer organisms and litter quality. It has been suggested that the decomposer community may be locally adapted to litter quality, providing a home‐field advantage (HFA) resulting in accelerated decomposition of local compared to non‐local litter, after accounting for decomposition differences due to litter quality and the functional capacity of microorganisms. Although widely tested in forests, this hypothesis remains controversial and lacks support of its generality across climates.We therefore tested the HFA hypothesis for litter decomposition in four contrasting ecosystems along an extensive climatic gradient in Chile, using a translocation experiment involving litter from 20 species. In addition to comparing mass loss, we adopted a novel way to disentangle decomposer effects from climate effects, based on loss rates of elements that are actively released from the litter by decomposers during its breakdown versus elements that are simply leached by precipitation. We used the ratios of nitrogen and potassium losses (N/K loss) and phosphorus and potassium losses (P/K loss) to unravel the relative role of microbial breakdown (N and P loss) versus physical leaching (K loss) along the climate gradient. Thus, at each site, we tested whether litter mass loss, N/K loss and P/K loss presented an additional loss due to a HFA for local compared to non‐local litter.Across a wide range of environments and litter types, our findings unequivocally contradicted the HFA hypothesis. We observed no significantly positive HFA along the gradient; however, litter quality and the general ability of the decomposer community influenced litter decomposition much more strongly than origin or location of the litter.Our study questions the applicability of the HFA for litter decomposition and calls for more studies that include a large range of climatic conditions to understand the context‐dependency of HFA. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Deschampsia antarctica is one of the only two native vascular plants in Antarctica, mostly located in the ice-free areas of the Peninsula's coast and adjacent islands. This region is characterized by a short growing season, frequent extreme climatic events, and soils with reduced nutrient availability. However, it is unknown whether its photosynthetic and stress tolerance mechanisms are affected by the availability of nutrients to deal with this particular environment. We studied the photosynthetic, primary metabolic, and stress tolerance performance of D. antarctica plants growing on three close sites (<500 m) with contrasting soil nutrient conditions. Plants from all sites showed similar photosynthetic rates, but mesophyll conductance and photobiochemistry were more limiting (~25%) in plants growing on low-nutrient availability soils. Additionally, these plants showed higher stress levels and larger investments in photoprotection and carbon pools, most probably driven by the need to stabilize proteins and membranes, and remodel cell walls. In contrast, when nutrients were readily available, plants shifted their carbon investment towards amino acids related to osmoprotection, growth, antioxidants, and polyamines, leading to vigorous plants without appreciable levels of stress. Taken together, these findings demonstrate that D. antarctica displays differential physiological performances to cope with adverse conditions depending on resource availability, allowing it to maximize stress tolerance without jeopardizing photosynthetic capacity. [ABSTRACT FROM AUTHOR]