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The structural and functional traits of coniferous trees can reflect their growth states and adaptive strategies to a harsh environment. However, it is still unclear if and how hydraulic traits of subalpine conifers change with altitude.Therefore, the changes in stem hydraulic characteristics of Abies fabri along an elevational gradient (2700–3700 m a.s.l.) were identified in a subalpine ecosystem in southwest China and linked to anatomical properties.Xylem hydraulic efficiency decreased with increasing elevation. Surprisingly, higher hydraulic dysfunction and vulnerability to embolism occurred at higher altitudes. The trade‐off between hydraulic efficiency and safety was weak in A. fabri at higher elevations. Low temperature and superfluous precipitation may be the main constraints for hydraulic function and mechanical strength ((t/b)2)) in plants at high elevations (p < 0.05). The strongly limited hydraulic transport system reflected the severe growth constraint of A. fabri at high elevations. Although series of anatomical traits varied with elevation (e.g. smaller mean diameter of tracheid, mean hydraulic conduit diameter and mean pit aperture diameter at higher altitude) and revealed the adaptive strategies to enhance embolism resistance, thickness‐to‐span ratio ((t/b)2) played a dominant role in the trade‐off between hydraulic efficiency and safety. Thickness‐to‐span ratio was positively correlated with stem hydraulic conductivity but negatively correlated with percent loss of conductivity and water potential at 50% loss of conductivity, (t/b)2 and specific leaf area. Therefore, plants with better hydraulic and growth states at low elevations could allocate more resources to building up solid mechanical supporting systems to cope with high wind load, while those at high elevations with impaired growth states and limited hydraulic functions had to invest more resources in leaves under the harsh environment. The weak trade‐off between hydraulic efficiency and safety (lower hydraulic efficiency and high risk of embolism) could limit the growth and distribution of A. fabri at timberlines; however, global warming trends may facilitate hydraulic transport and benefit plants' growth in the future. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

It is a challenge to scale‐up from simplified proxies to ecosystem functioning since the inherent complexity of natural ecosystems hinders such an approach. One way to address this complexity is to track ecosystem processes through the lens of plant functional traits. Elevational gradients with diverse biotic and abiotic conditions offer ideal settings for inferring functional trait responses to environmental gradients globally. However, most studies have focused on differences in mean trait values among species, and little is known on how intraspecific traits vary along wide elevational gradients and how this variability reflects ecosystem productivity.We measured functional traits of the sub‐shrub Koenigia mollis (Basionym: Polygonum molle; a widespread species) in 11 populations along a wide elevational gradient (1515–4216 m) considering from subtropical forest to alpine treeline in the central Himalayas. After measuring different traits (plant height, specific leaf area, leaf area, length of flowering branches, leaf carbon isotope (δ13C), leaf carbon and leaf nitrogen concentrations), we investigated drivers on changes of these traits and also characterized their relationships with elevation, climate and ecosystem productivity.All trait values decreased with increasing elevation, except for δ13C that increased upwards. Likewise, most traits showed strong positive relationships with potential evapotranspiration, while δ13C exhibited a negative relationship. In this context, elevation‐dependent water–energy dynamics is the primary driver of trait variations. Furthermore, six key traits (plant height, length of flowering branch, specific leaf area, leaf carbon, leaf nitrogen and leaf δ13C) explained 90.45% of the variance in ecosystem productivity.Our study evidences how elevation‐dependent climate variations affect ecosystem processes and functions. Intraspecific variability in leaf functional traits is strongly driven by changes in water–energy dynamics, and reflects changes in ecosystem productivity over elevation. K. mollis, with one of the widest elevational gradients known to date, could be a model species to infer functional trait responses to environmental gradients globally. As inferred from K. mollis, the water–energy dynamics can be a hydrothermal variable to understand the formation of vegetation boundaries, such as alpine treeline. This study sheds new insight on how plants modify their basic ecological strategies to cope with changing environments. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Variation in leaf functional traits along environmental gradients can reveal how vascular epiphytes respond to broad‐ and small‐scale environmental gradients. Along elevational gradients, both temperature and precipitation likely play an important role as drivers of leaf trait variation, but these traits may also respond to small‐scale changes in light, temperature and humidity along the vertical environmental gradient within forest canopies. However, the relative importance of broad‐ and small‐scale environmental gradients as drivers of variation in leaf functional traits of vascular epiphytes is poorly understood.Here, we examined variation in morphological and chemical leaf traits of 102 vascular epiphyte species spanning two environmental gradients along Cofre de Perote mountain in Mexico: (i) a broad‐scale environmental gradient approximated by elevation as well as by species' lower and upper elevational limits, and (ii) small‐scale environmental gradients using the relative height of attachment of an epiphyte on a host tree as a proxy for variation in environmental conditions within the forest canopy. We also assessed whether variation in morphological and chemical leaf traits along these gradients was consistent across photosynthetic pathways (CAM and C3).Broad‐ and small‐scale environmental gradients explained more variation in chemical traits (marginal R2: 11%–89%) than in morphological traits (marginal R2: 2%–31%). For example, leaf carbon isotope signatures (δ13C), which reflects water‐use efficiency, varied systematically across both environmental gradients, suggesting a decrease in water‐use efficiency with increasing lower and upper elevational limits and an increase in water‐use efficiency with relative height of attachment. The influence of lower and upper elevational limits on trait variation differed between photosynthetic pathways, except for leaf dry matter content and leaf nitrogen‐to‐phosphorus ratio. Contrary to our expectations, broad‐ and small‐scale environmental gradients explained minimal variation in morphological leaf traits, suggesting that environmental conditions do not constrain morphological leaf trait values of vascular epiphytes.Our findings suggest that assessing multiple drivers of leaf trait variation among photosynthetic pathways is key for disentangling the mechanisms underlying responses of vascular epiphytes to environmental conditions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Positive biotic interactions between plant species may strongly affect species and community‐level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant–plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant–plant interactions, has rarely been explored.Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation.Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant–plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation.This research, therefore, suggests that benefactor species' facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat modification or increased resource availability by benefactor species into positive impacts on beneficiary species. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Partner choice in species interaction networks, that is, between frugivorous birds and fruiting plants, is largely determined by matching of functional traits. However, the composition of functional traits in plant communities changes along land‐use gradients. Understanding how flexible consumers react to changes in the trait composition of resources is crucial to project consequences for ecosystem functions, such as seed dispersal.We investigated the ability of birds to consume fruits with different sets of traits in natural and fragmented tropical montane forests across an elevational gradient. We developed a novel, trait‐based approach to quantify the functional shifts of consumers between resources with different functional traits. We expected the degree of functional shifts to be associated with bird traits related to food choice, such as bill width and degree of frugivory, as well as foraging behaviour, such as wing shape and foraging stratum.We sampled the plant–frugivore networks at three elevations and two habitat types (natural and fragmented forest) and measured the functional traits for each plant and bird species. We calculated the trait space of the plant community at each elevation and projected the interacting birds into it. Finally, we calculated the functional shift, which is the trait‐based distance between the preferred fruit resources in the two habitat types for each bird species.We found differences in the functional trait space of the fruiting plant community between natural and fragmented forests across all elevations. Birds' observed functional shifts between habitat types at each elevation were generally larger than the shifts expected by null models. Wing shape was the most important trait related to the functional shifts across the elevational gradient, whereas bill width, degree of frugivory, foraging stratum and phylogeny were not important.We conclude that birds with pointed wings respond flexibly to changes in the trait composition of fruit resources, probably due to the high mobility of these species. Our results emphasize that linking species interaction networks and functional trait analyses yield new insights into how consumer species respond to changes in biotic factors and can improve projections of how human impacts modify trophic interactions and associated ecosystem functions. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

Physiological and energetic mechanisms have been proposed to constrain body sizes of organisms along climatic gradients; however, these provide contrasting predictions. While Bergmann's rule predicts increases in body sizes in cooler climates resulting from physiological constraints, energy-based community assembly rules suggest declines in the mean body size of species caused by increased extinction probabilities for large-bodied species in low-energy habitats., We tested these contrasting hypotheses by quantifying trait distributions in bee communities along a 3·6-km elevational gradient at Mt. Kilimanjaro. Traditionally, intra- and interspecific trait shifts along environmental gradients have been investigated in isolation. However, a surge of theoretical approaches and studies on plants demonstrated that the explicit integration of trait variation among and within species can be essential for identifying the mechanisms that shape traits and related ecosystem functions along environmental gradients. We therefore studied variation in body size and related morphological traits at both the intra- and interspecific level., We found support for both physiological constraints and energy-based community assembly rules as drivers of trait distribution in bee communities along elevational gradients, which, however, affected different levels of biotic organization, that is the population and community level. While the number of bee species with large body sizes declined with elevation, individuals within species became on average larger, resulting in contrasting trends in morphometric parameters at the community versus population level., Furthermore, body size within bee communities became less variable at higher elevations, largely as a result of a non-random, directive loss of species, but paralleled by a decline in intraspecific variance, suggesting intensified filtering effects with increasing elevation. Similar patterns were found for other functional traits related to the foraging ecology of bees (tongue length, relative forewing length)., We conclude that along climatic gradients both physiological and energetic constraints shape trait distributions of pollinators, but at different levels of biological organization., A is available for this article. [ABSTRACT FROM AUTHOR]

Spatial variation in filters imposed by the abiotic environment causes variation in functional traits within and among plant species. This is abundantly clear for plant species along elevational gradients, where parallel abiotic selection pressures give rise to predictable variation in leaf phenotypes among ecosystems. Understanding the factors responsible for such patterns may provide insight into the current and future drivers of biodiversity, local community structure and ecosystem function., In order to explore patterns in trait variation along elevational gradients, we conducted a meta-analysis of published observational studies that measured three key leaf functional traits that are associated with axes of variation in both resource competition and stress tolerance: leaf mass:area ratio ( LMA), leaf nitrogen content per unit mass ( Nmass) and N content per unit area ( Narea). To examine whether there may be evidence for a genetic basis underlying the trait variation, we conducted a review of published results from common garden experiments that measured the same leaf traits., Within studies, LMA and Narea tended to decrease with mean annual temperature ( MAT) along elevational gradients, while Nmass did not vary systematically with MAT. Correlations among pairs of traits varied significantly with MAT: LMA was most strongly correlated with Nmass and Narea at high-elevation sites with relatively lower MAT. The strengths of the relationships were equal or greater within species relative to the relationships among species, suggesting parallel evolutionary dynamics along elevational gradients among disparate biomes. Evidence from common garden studies further suggests that there is an underlying genetic basis to the functional trait variation that we documented along elevational gradients., Taken together, these results indicate that environmental filtering both selects locally adapted genotypes within plant species and constrains species to elevational ranges based on their ranges of potential leaf trait values. If individual phenotypes are filtered from populations in the same way that species are filtered from regional species pools, changing climate may affect both the species and functional trait composition of plant communities. [ABSTRACT FROM AUTHOR]

Despite widespread focus on interspecific variation in trait-based ecology, there is growing evidence that intraspecific trait variability can play a fundamental role in plant community responses to environmental change and community assembly., Here, we quantify the strength and direction of inter- and intraspecific plant community trait responses along a 900 m elevation gradient spanning alpine and subalpine plant communities in southern New Zealand. We measured five commonly used leaf traits (i.e. dry matter content, N and P concentrations, leaf area and specific leaf area) on all 31 dominant and subordinate species recorded along the gradient, and examined their species-specific and community-level responses to elevation using both abundance-weighted and nonweighted averages of trait values., By decomposing the variance of community-level measures of these traits across the gradient, we showed that the contribution of interspecific variation to the response of plant assemblages to elevation was stronger than that of intraspecific variation, for all traits except specific leaf area. Further, the relative contributions of interspecific effects were greater when abundance-weighted rather than nonweighted measures were used. We also observed contrasting intraspecific trait responses to the gradient among species (particularly for leaf N and P concentrations), and found both positive and negative covariation between inter- and intraspecific effects on community-level trait values., The weak community-average trait responses to elevation, as found for specific leaf area ( SLA) and leaf N and P concentrations, resulted from strong but opposing responses among vs. within species, which are not typically accounted for in species-based measures of plant community responses. For instance, increasing elevation (and associated factors such as a decrease in soil nutrient availability) favoured the dominance of species with relatively high leaf nutrient concentrations while simultaneously triggering an intraspecific decrease in the leaf nutrient concentrations of these species., The context dependency of positive and negative covariation between inter- and intraspecific trait variability, and the species-specific nature of intraspecific shifts in functional trait values, reveal highly complex plastic responses of plants to environmental changes, and highlights the need for greater consideration of the role that intraspecific variation plays in community-level processes. [ABSTRACT FROM AUTHOR]

1. Improving our knowledge on plant functions underlying shifts in species ranges along altitudinal and latitudinal gradients is a research priority to understand biotic responses to climate change. Although much is known about biological responses to elevation, coupled observations of ecophysiological and reproductive traits with whole-plant performance metrics are rare, and thus our understanding disjunct rather than holistic. 2. We expected growth and reproductive performance to decrease with elevation, irrespective of adjustments in traits, modifications in allocation, or congeneric shifts in populations. To test this hypothesis we assessed growth, reproductive investments and traits related to resource use efficiency and reproductive success in populations of two vicariant species growing along an elevation gradient: Saxifraga trifurcata (lowland species) and S. canaliculata (highland species). 3. For most metrics, a relationship with elevation arose, mostly related to the replacement of species, but also to within-species variation in S. trifurcata. Leaves of S. canaliculata, and of the higher populations of S. trifurcata, were denser, had lower specific leaf area (SLA) and lower N concentration but higher N resorption efficiency. Collectively, these trends indicate a more conservative resource use pattern at the highlands as compared to the lowlands. Despite this, vegetative growth per unit canopy area was higher in S. canaliculata than in S. trifurcata, and in the highland than lowland populations of S. trifurcata. Reproductive investments, measured as the reproductive mass per unit canopy area, were lower, and reproductive maturity was reached later, in S. canaliculata, but reproductive success (fruit set and seed germination) increased at the high altitude limit of each species’ range. 4. Performance did not uniformly decrease with altitude. Growth was higher in the uplands possibly because preferential biomass and meristem allocation to the vegetative function compensated for the decrease in growth season length. Similarly, the decrease in reproductive investments in the highland populations was partially compensated for, since fruit set was higher and more viable seeds (per gram invested in reproduction) were produced in the highland limit of each species. 5. This suggests that populations growing in increasingly limiting environments can partially compensate by modifications in allocation and morpho-functional traits. [ABSTRACT FROM AUTHOR]