Suite Of Traits Research Articles

Molar crenulation trait definition and variation in modern human populations

Crenulated molars have been used extensively in biological anthropology. However, the trait has not been formally defined, nor have population frequencies been thoroughly outlined. This study provides a formal definition of molar crenulations and data on their presence in a large sample. Data were collected on maxillary and mandibular molars of modern dental material from various populations: South African, Hispanic, Japanese, American White, and American Black (n = 750). Molar crenulations were defined and a rank-scale created. Statistical analyses include chi-squared, correspondence analysis, and trait correlations. Significant statistical differences were found between populations in all molars. Minimal sexual dimorphism was noted, and is most pronounced among the American Black sample. Generally, American White and Japanese samples showed lower frequencies of molar crenulations, the highest frequencies were seen in the American Black and South African samples, and the Hispanic sample was intermediate. Correspondence analysis showed that American Black samples tended towards grade 2, and South African samples were more often a grade 1. American White and Japanese samples were most often grade 0, and Hispanic samples were intermediate. Correlations were noted across the molars. Population differences exist in the presence of molar crenulations, which were likely shaped by evolution. Based on these results molar crenulations can be added to the suite of traits currently used to study population differences.

Biotic constraints on Cactoblastis cactorum (Berg) host use in the southern US and their implications for future spread

The roles of biotic interactions in determining invasion success emerge from the set of traits possessed by the invader and those present in the community being invaded. Identifying traits important for governing invader distributions is challenging, but systems in which invaders specialize on hosts or resources may facilitate narrowed focus on particular suites of traits. Most examples of specialist consumers that become successful invaders are escaped biological control species. One example is the South American cactus moth (Cactoblastis cactorum), an escaped biological control agent that infests prickly-pear cacti (primarily taxa in the genus Opuntia). Here we quantify tissue macronutrient traits (crude fiber, lipid, crude protein, and carbohydrate by difference) and evaluate C. cactorum infestation of several North American Opuntia taxa as a function of those traits. We then evaluate whether a common, native cactus moth (Melitara prodenialis) infests plants that are similar to those used by C. cactorum to evaluate the likelihood that the species compete for hosts. Our results generally suggest that Opuntia tissue macronutrients may be important traits in mediating cactus moth-Opuntia associations. While the range of macronutrients that are suitable for M. prodenialis are largely similar to those for C. cactorum in the east, M. prodenialis tend to infest plants with higher crude fiber content than C. cactorum. Tissue crude fiber content may thus play an important role in both constraining infestation of host plants by C. cactorum in its current invasive range as well as determining its future spread in North America.

Different traits predict competitive effect versus response by Bromus madritensis in its native and invaded ranges

Community assembly and coexistence theories predict that both fitness and plant functional traits should influence competitive interactions between native and invasive species. The evolution of the increased competitive ability hypothesis predicts that species will grow larger (a measure of fitness) in their invaded than native range; hence we hypothesized that species might exert greater competitive effects in their invaded range, lessening the importance of functional traits for competitive outcomes. In a greenhouse experiment we compared traits and competitive interactions between Bromus madritensis (an annual grass) and resident species from its native range in Spain, and its invaded range in Southern California. As predicted, B. madritensis collected in California grew larger and had a greater competitive effect on resident species than B. madritensis collected in Spain. However, residents from California also suppressed the growth of B. madritensis more than species from its native range in Spain. Competitive interaction strengths were predicted by different suites of traits in the native versus invaded range of B. madritensis; surprisingly, however, size of the resident species (fitness), did not predict variation in competitive interactions. This study shows that different suites of traits may aid in identifying those native species likely to strongly compete with invaders, versus those that will be competitively suppressed by invaders, with important implications for the design of restoration efforts aimed at promoting native species growth and preventing invasion. More generally, our study shows that fitness differences may not be as important as traits when predicting competitive outcomes in this system.

Genetic and Developmental Basis for Increased Leaf Thickness in the Arabidopsis Cvi Ecotype.

Leaf thickness is a quantitative trait that is associated with the ability of plants to occupy dry, high irradiance environments. Despite its importance, leaf thickness has been difficult to measure reproducibly, which has impeded progress in understanding its genetic basis, and the associated anatomical mechanisms that pattern it. Here, we used a custom-built dual confocal profilometer device to measure leaf thickness in the Arabidopsis Ler × Cvi recombinant inbred line population and found statistical support for four quantitative trait loci (QTL) associated with this trait. We used publically available data for a suite of traits relating to flowering time and growth responses to light quality and show that three of the four leaf thickness QTL coincide with QTL for at least one of these traits. Using time course photography, we quantified the relative growth rate and the pace of rosette leaf initiation in the Ler and Cvi ecotypes. We found that Cvi rosettes grow slower than Ler, both in terms of the rate of leaf initiation and the overall rate of biomass accumulation. Collectively, these data suggest that leaf thickness is tightly linked with physiological status and may present a tradeoff between the ability to withstand stress and rapid vegetative growth. To understand the anatomical basis of leaf thickness, we compared cross-sections of Cvi and Ler leaves and show that Cvi palisade mesophyll cells elongate anisotropically contributing to leaf thickness. Flow cytometry of whole leaves show that endopolyploidy accompanies thicker leaves in Cvi. Overall, our data suggest that mechanistically, an altered schedule of cellular events affecting endopolyploidy and increasing palisade mesophyll cell length contribute to increase of leaf thickness in Cvi. Ultimately, knowledge of the genetic basis and developmental trajectory leaf thickness will inform the mechanisms by which natural selection acts to produce variation in this adaptive trait.

Signatures of Selection on Standing Genetic Variation Underlie Athletic and Navigational Performance in Racing Pigeons.

Racing pigeons have been selectively bred to find their way home quickly over what are often extremely long distances. This breed is of substantial commercial value and is also an excellent avian model to gain empirical insights into the evolution of traits associated with flying performance and spatial orientation. Here, we investigate the molecular basis of the superior athletic and navigational capabilities of racing pigeons using whole-genome and RNA sequencing data. We inferred multiple signatures of positive selection distributed across the genome of racing pigeons. The strongest signature overlapped the CASK gene, a gene implicated in the formation of neuromuscular junctions. However, no diagnostic alleles were found between racing pigeons and other breeds, and only a small proportion of highly differentiated variants were exclusively detected in racing pigeons. We can thus conclude that very few individual genetic changes, if any, are either strictly necessary or sufficient for superior athletics and navigation. Gene expression analysis between racing and nonracing breeds revealed modest differences in muscle (213) and brain (29). These transcripts, however, showed only slightly elevated levels of genetic differentiation between the two groups, suggesting that most differential expression is not causative but likely a consequence of alterations in regulatory networks. Our results show that the unique suite of traits that enable fast flight, long endurance, and accurate navigation in racing pigeons, do not result from few loci acting as master switches but likely from a polygenic architecture that leveraged standing genetic variation available at the onset of the breed formation.

Syndromes in suites of correlated traits suggest multiple mechanisms facilitating invasion in a plant range-expander

Various mechanisms can facilitate the success of plant invasions simultaneously, but may be difficult to disentangle. In the present study, plants of the range-expanding species Bunias orientalis from native, invasive and naturalised, not yet invasive populations were compared in a field common garden over two years. Plants were grown under two nitrate-regimes and multiple traits regarding growth, defence, antagonist loads and reproduction were measured. A rank-based clustering approach was used to assign correlated traits to distinct suites. These suites were analysed for “syndromes” that are expressed as a function of population origin and/or fertilisation treatment and might represent different invasion mechanisms. Indeed, distinct suites of traits were differentially affected by these factors. The results suggest that several pre-adaptation properties, such as certain growth characteristics and intraspecific chemical variation, as well as post-introduction adaptations to antagonists and resource availability in novel habitats, are candidate mechanisms that facilitate the success of invasive B. orientalis in parallel. It was concluded that rank-based clustering is a robust and expedient approach to integrate multiple traits for elucidating invasion syndromes within individual species. Studying a multitude of traits at different life-history and establishment stages of plants grown under distinct resource treatments reveals species-specific trade-offs and resource sinks and simplifies the interpretation of trait functions for the potential invasive success of plants.

Factors driving metabolic diversity in the budding yeast subphylum

BackgroundAssociations between traits are prevalent in nature, occurring across a diverse range of taxa and traits. Individual traits may co-evolve with one other, and these correlations can be driven by factors intrinsic or extrinsic to an organism. However, few studies, especially in microbes, have simultaneously investigated both across a broad taxonomic range. Here we quantify pairwise associations among 48 traits across 784 diverse yeast species of the ancient budding yeast subphylum Saccharomycotina, assessing the effects of phylogenetic history, genetics, and ecology.ResultsWe find extensive negative (traits that tend to not occur together) and positive (traits that tend to co-occur) pairwise associations among traits, as well as between traits and environments. These associations can largely be explained by the biological properties of the traits, such as overlapping biochemical pathways. The isolation environments of the yeasts explain a minor but significant component of the variance, while phylogeny (the retention of ancestral traits in descendant species) plays an even more limited role. Positive correlations are pervasive among carbon utilization traits and track with chemical structures (e.g., glucosides and sugar alcohols) and metabolic pathways, suggesting a molecular basis for the presence of suites of traits. In several cases, characterized genes from model organisms suggest that enzyme promiscuity and overlapping biochemical pathways are likely mechanisms to explain these macroevolutionary trends. Interestingly, fermentation traits are negatively correlated with the utilization of pentose sugars, which are major components of the plant biomass degraded by fungi and present major bottlenecks to the production of cellulosic biofuels. Finally, we show that mammalian pathogenic and commensal yeasts have a suite of traits that includes growth at high temperature and, surprisingly, the utilization of a narrowed panel of carbon sources.ConclusionsThese results demonstrate how both intrinsic physiological factors and extrinsic ecological factors drive the distribution of traits present in diverse organisms across macroevolutionary timescales.

The potential for host switching via ecological fitting in the emerald ash borer-host plant system.

The traits used by phytophagous insects to find and utilize their ancestral hosts can lead to host range expansions, generally to closely related hosts that share visual and chemical features with ancestral hosts. Host range expansions often result from ecological fitting, which is the process whereby organisms colonize and persist in novel environments, use novel resources, or form novel associations with other species because of the suites of traits that they carry at the time they encounter the novel environment. Our objective in this review is to discuss the potential and constraints on host switching via ecological fitting in emerald ash borer, Agrilus planipennis, an ecologically and economically important invasive wood boring beetle. Once thought of as an ash (Fraxinus spp.) tree specialist, recent studies have revealed a broader potential host range than was expected for this insect. We discuss the demonstrated host-use capabilities of this beetle, as well as the potential for and barriers to the adoption of additional hosts by this beetle. We place our observations in the context of biochemical mechanisms that mediate the interaction of these beetles with their host plants and discuss whether evolutionary host shifts are a possible outcome of the interaction of this insect with novel hosts.

Technical Note: The Definition of New Dental Morphological Variants Related to Malocclusion

Since the codification of the Arizona State University Dental Anthropology System over 25 years ago, few additional morphological traits have been defined. This work serves to expand the current suite of traits currently collected by biological anthropologists. These traits surround various issues of malocclusion and follow clinical definitions of these traits as well as incorporate observed population variation in character states. These traits include issues of spacing (i.e., diastema and crowding) as well as mandibular and maxillary occlusion (i.e., overbite, underbite). A discussion of the etiology and utility of these traits in bioarchaeological and forensic anthropological research is also given.

Evidence for dispersal syndromes in freshwater fishes.

Dispersal is a fundamental process defining the distribution of organisms and has long been a topic of inquiry in ecology and evolution. Emerging research points to an interdependency of dispersal with a diverse suite of traits in terrestrial organisms, however the extent to which such dispersal syndromes exist in freshwater species remains uncertain. Here, we test whether dispersal in freshwater fishes (1) is a fixed property of species, and (2) correlates with life-history, morphological, ecological and behavioural traits, using a global dataset of dispersal distances collected from the literature encompassing 116 riverine species and 196 locations. Our meta-analysis revealed a high degree of repeatability and heritability in the dispersal estimates and strong associations with traits related to life-history strategies, energy allocation to reproduction, ecological specialization and swimming skills. Together, these results demonstrate that similar to terrestrial organisms, the multi-dimensional nature of dispersal syndromes in freshwater species offer opportunities for the development of a unifying paradigm of movement ecology that transcend taxonomic and biogeographical realms. The high explanatory power of the models also suggests that trait-based and phylogenetic approaches hold considerable promises to inform conservation efforts in a rapidly changing world.

Spatial patterns and climate relationships of major plant traits in the New World differ between woody and herbaceous species

AbstractAimDespite several recent efforts to map plant traits and to identify their climatic drivers, there are still major gaps. Global trait patterns for major functional groups, in particular, the differences between woody and herbaceous plants, have yet to be identified. Here, we take advantage of big data efforts to compile plant species occurrence and trait data to analyse the spatial patterns of assemblage means and variances of key plant traits. We tested whether these patterns and their climatic drivers are similar for woody and herbaceous plants.LocationNew World (North and South America).MethodsUsing the largest currently available database of plant occurrences, we provide maps of 200 × 200 km grid‐cell trait means and variances for both woody and herbaceous species and identify environmental drivers related to these patterns. We focus on six plant traits: maximum plant height, specific leaf area, seed mass, wood density, leaf nitrogen concentration and leaf phosphorus concentration.ResultsFor woody assemblages, we found a strong climate signal for both means and variances of most of the studied traits, consistent with strong environmental filtering. In contrast, for herbaceous assemblages, spatial patterns of trait means and variances were more variable, the climate signal on trait means was often different and weaker.Main conclusionTrait variations for woody versus herbaceous assemblages appear to reflect alternative strategies and differing environmental constraints. Given that most large‐scale trait studies are based on woody species, the strikingly different biogeographic patterns of herbaceous traits suggest that a more synthetic framework is needed that addresses how suites of traits within and across broad functional groups respond to climate.

Correlated evolution between climate and suites of traits along a fast-slow continuum in the radiation of Protea.

Evolutionary radiations are responsible for much of Earth's diversity, yet the causes of these radiations are often elusive. Determining the relative roles of adaptation and geographic isolation in diversification is vital to understanding the causes of any radiation, and whether a radiation may be labeled as “adaptive” or not. Across many groups of plants, trait–climate relationships suggest that traits are an important indicator of how plants adapt to different climates. In particular, analyses of plant functional traits in global databases suggest that there is an “economics spectrum” along which combinations of functional traits covary along a fast–slow continuum. We examine evolutionary associations among traits and between trait and climate variables on a strongly supported phylogeny in the iconic plant genus Protea to identify correlated evolution of functional traits and the climatic‐niches that species occupy. Results indicate that trait diversification in Protea has climate associations along two axes of variation: correlated evolution of plant size with temperature and leaf investment with rainfall. Evidence suggests that traits and climatic‐niches evolve in similar ways, although some of these associations are inconsistent with global patterns on a broader phylogenetic scale. When combined with previous experimental work suggesting that trait–climate associations are adaptive in Protea, the results presented here suggest that trait diversification in this radiation is adaptive.

Ecology of Floristic Quality Assessment: testing for correlations between coefficients of conservatism, species traits and mycorrhizal responsiveness.

Many plant species are limited to habitats relatively unaffected by anthropogenic disturbance, so protecting these undisturbed habitats is essential for plant conservation. Coefficients of conservatism (C values) were developed as indicators of a species' sensitivity to anthropogenic disturbance, and these values are used in Floristic Quality Assessment as a means of assessing natural areas and ecological restoration. However, assigning of these values is subjective and improved quantitative validation of C values is needed. We tested whether there are consistent differences in life histories between species with high and low C values. To do this, we grew 54 species of tallgrass prairie plants in a greenhouse and measured traits that are associated with trade-offs on the fast-slow continuum of life-history strategies. We also grew plants with and without mycorrhizal fungi as a test of these species' reliance on this mutualism. We compared these traits and mycorrhizal responsiveness to C values. We found that six of the nine traits we measured were correlated with C values, and together, traits predicted up to 50 % of the variation in C values. Traits including fast growth rates and greater investment in reproduction were associated with lower C values, and slow growth rates, long-lived leaves and high root:shoot ratios were associated with higher C values. Additionally, plants with high C values and a slow life history were more responsive to mutualisms with mycorrhizal fungi. Overall, our results connect C values with life-history trade-offs, indicating that high C value species tend to share a suite of traits associated with a slow life history.

New insights into plants co‐existence in species‐rich communities: The pollination interaction perspective

AbstractQuestionsIn animal‐mediated pollination, pollinators can be regarded as a limiting resource for which entomophilous plant species might interact to assure pollination, an event pivotal for their reproduction and population maintenance. At community level, spatially aggregated co‐flowering species can thus be expected to exhibit suitable suites of traits to avoid competition and ensure pollination. We explored the problem by answering the following questions: (1) are co‐flowering species specialized on different guilds of pollinators; (2) do co‐flowering pollinator‐sharing species segregate spatially; and (3) do co‐flowering pollinator‐sharing species that diverge in anther position spatially aggregate more than those that converge in anther position?Study SiteEuganean Hills,NEItaly.MethodsPlant composition, flowering phenology and interactions between each entomophilous plant species and pollinating insects were monitored every 15 days in 40 permanent plots placed in an area of 16 ha. We quantified the degree of flowering synchrony, pollinator‐sharing and spatial aggregation between each pair of entomophilous species. We then tested the relationship between the degree of co‐flowering, pollinator‐sharing and spatial aggregation, and between spatial aggregation and anther position.ResultsEntomophilous species converged, at least partially in flowering time, and the phenological synchronization of flowering was significantly associated with the sharing of pollinator guilds. Co‐flowering pollinator‐sharing species segregated spatially. Furthermore, co‐flowering pollinator‐sharing species that diverged in anther position aggregated more than those that converged in anther position.ConclusionsReproductive traits that facilitate the co‐existence of co‐flowering species include specialization on different pollinator guilds and a phenological displacement of the flowering time. Furthermore, in circumstances of increased competition due to phenological synchronization, pollinator‐sharing and spatial aggregation, the chance of effective pollination might depend on differences in anther position, resulting in a divergent pollen placement on pollinator bodies. One of the most interesting results we obtained is that the presence of one mechanism does not preclude the operation of others, and each plant species can simultaneously exhibit different strategies. Although more studies are needed, our results can provide additional information about plant–plant interactions and provide new insights into mechanisms allowing the co‐existence of a high number of plant species in local communities.

Effects of disturbance frequency and severity on plant traits: An assessment across a temperate flora

Abstract Recent analyses of plant traits across large sets of species have revolutionized our understanding of plant functional differentiation. However, understanding of ecological relevance of this differentiation is contingent upon knowledge of environmental preferences of species, namely along gradients of disturbance and productivity for which no quantitative data were available until recently. We examined the relationships of key functional traits (life‐history categories, leaf‐height‐seed (LHS) traits, clonal growth and bud bank traits) in the herb‐dominated flora of Central Europe to species niche positions along the gradients of disturbance frequency, disturbance severity and productivity. Life‐history categories and bud bank size showed the strongest response to disturbance and productivity, whereas relationship of LHS traits was much weaker. A number of traits, including clonal growth form and bud bank size, showed a significantly unimodal response to disturbance frequency. Responses of many traits to disturbance frequency were different from their responses to disturbance severity. Our findings support the notions that disturbance and productivity are key gradients of species functional differentiation and that disturbance severity and frequency select for different trait suites. Furthermore, the data indicate that in a predominantly herbaceous flora, the traits of life span, clonal growth and resprouting show stronger relationship with the environment than the LHS traits, which are more important in floras with high proportions of woody species. Since most previous trait analyses are based on woody‐plant‐dominated floras, patterns revealed in a herb‐dominated flora deepen our understanding of the full range of variation within the plant kingdom. A plain language summary is available for this article.

Live long and prosper: plant-soil feedback, lifespan, and landscape abundance covary.

Plant soil feedbacks (PSFs) are thought to be important to plant growth and species coexistence, but most support for these hypotheses is derived from short-term greenhouse experiments. Here we use a seven-year, common garden experiment to measure PSFs for seven native and six nonnative species common to the western United States. We use these long-term, field-based estimates to test correlations between PSF and plant landscape abundance, species origin, functional type, and lifespan. To assess potential PSF mechanisms, we also measured soil microbial community composition, root biomass, nitrogen cycling, bulk density, penetration resistance, and shear strength. Plant abundance on the landscape and plant lifespan were positively correlated with PSFs, though this effect was due to the relationships for native plants. PSFs were correlated with indices of soil microbial community composition. Soil nutrient and physical traits and root biomass differed among species but were not correlated with PSF. While results must be taken with caution because only 13 species were examined, these species represent most of the dominant plant species in the system. Results suggest that native plant abundance is associated with the ability of long-lived plants to create positive plant-soil microbe interactions, while short-lived nonnative plants maintain dominance by avoiding soil-borne antagonists, increasing nitrogen cycling and dedicating resources to aboveground growth and reproduction rather than to belowground growth. Broadly, results suggest that PSFs are correlated with a suite of traits that determine plant abundance.

Edaphic history over seedling characters predicts integration and plasticity of integration across geologically variable populations of Arabidopsis thaliana.

Studies on phenotypic plasticity and plasticity of integration have uncovered functionally linked modules of aboveground traits and seedlings of Arabidopsis thaliana, but we lack details about belowground variation in adult plants. Functional modules can be comprised of additional suites of traits that respond to environmental variation. We assessed whether shoot and root responses to nutrient environments in adult A. thaliana were predictable from seedling traits or population-specific geologic soil characteristics at the site of origin. We compared 17 natural accessions from across the native range of A. thaliana using 14-day-old seedlings grown on agar or sand and plants grown to maturity across nutrient treatments in sand. We measured aboveground size, reproduction, timing traits, root length, and root diameter. Edaphic characteristics were obtained from a global-scale dataset and related to field data. We detected significant among-population variation in root traits of seedlings and adults and in plasticity in aboveground and belowground traits of adult plants. Phenotypic integration of roots and shoots varied by population and environment. Relative integration was greater in roots than in shoots, and integration was predicted by edaphic soil history, particularly organic carbon content, whereas seedling traits did not predict later ontogenetic stages. Soil environment of origin has significant effects on phenotypic plasticity in response to nutrients, and on phenotypic integration of root modules and shoot modules. Root traits varied among populations in reproductively mature individuals, indicating potential for adaptive and integrated functional responses of root systems in annuals.

Correlated evolution of sexually selected traits: interspecific variation in ejaculates, sperm morphology, copulatory mate guarding, and body size in two sympatric species of garter snakes

Male reproductive success is dependent on a correlated suite of traits related to a species’ ecology and mating system dynamics. Closely related species differing in their mating systems and ecology, such as the garter snakes (Thamnophis), are ideal for studying the correlated evolution of sexually selected traits. Here, we compare the degree of sexual size dimorphism (SSD), copulatory behavior, copulatory plug size, and traits associated with sperm competition between two sympatric and closely related Thamnophis species, T. sirtalis and T. radix with divergent mating aggregation size and density. Our findings indicate that T. sirtalis has greater female-biased SSD, shorter copulations, and larger, more strongly adhering copulatory plugs than T. radix. Our finding that T. sirtalis have longer sperm and higher numbers of sperm per ejaculate is further evidence of more intense sperm competition in this species than in T. radix. However, this reduced number of sperm in the ejaculate means that T. radix males are likely capable of more matings per season than T. sirtalis. This result may reflect differences in feeding during the breeding season (obligate aphagy in T. sirtalis) and the potential for sperm loss in T. radix during prolonged copulations that are prevented in T. sirtlais by their substantial copulatory plugs. Our findings demonstrate that ecological and mating system dynamics have the capacity to strongly influence correlated selection of pre- and postcopulatory traits. Our findings demonstrate that ecological and mating system dynamics have the capacity to strongly influence correlated selection of, and trade-offs between, pre- and postcopulatory traits. For most postcopulatory selected traits we measured (sperm size, ejaculate size, effectiveness of their copulatory plug, and gamete-somatic index (but not relative testes mass)), the species predicted to experience strong sperm competition (T. sirtalis) has higher trait values. However, T. radix, which has a precopulatory mating advantage (larger male body size and less pronounced female-biased sexual size dimorphism), has enough stored sperm for many more matings. The large amount of stored sperm in T. radix may be due to sperm loss during prolonged matings or different energy budgets between the two species: T. sirtalis, with an evolutionary history of sperm competition, does not eat during the breeding season, which limits the time available for mating.

The relationships between leaf economics and hydraulic traits of woody plants depend on water availability

Leaf economics and hydraulic traits are simultaneously involved in the process of trading water for CO2, but the relationships between these two suites of traits remain ambiguous. Recently, Li et al. (2015) reported that leaf economics and hydraulic traits were decoupled in five tropical-subtropical forests in China.We tested the hypothesis that the relationships between economics and hydraulic traits may depend on water availability. We analysed five leaf economics traits, four hydraulic traits and anatomical structures of 47 woody species on the Loess Plateau with poor water availability and compared those data with Li et al. (2015) obtained in tropical-subtropical regions with adequate water.The results showed that plants on the Loess Plateau tend to have higher leaf tissue density (TD), leaf nitrogen concentrations and venation density (VD) and lower stomatal guard cell length (SL) and maximum stomatal conductance to water vapour (gwmax). VD showed positive correlations with leaf nitrogen concentrations, palisade tissue thickness (PT) and ratio of palisade tissue thickness to spongy tissue thickness (PT/ST). Principal component analysis (PCA) showed a result opposite from those of tropical-subtropical regions: leaf economics and hydraulic traits were coupled on the Loess Plateau.A stable correlation between these two suites of traits may be more cost-effective on the Loess Plateau, where water availability is poor. The correlation of leaf economics and hydraulic traits may be a type of adaptation mechanism in arid conditions.

Increases in CO2 from past low to future high levels result in “slower” strategies on the leaf economic spectrum

Depending on resource availability plants exhibit a specific suite of traits. At the interspecific level these traits follow the leaf economic spectrum (LES), traits related to slow turnover when resources are poor and fast turnover when resources are plentiful. Limited data shows that within species, CO2 availability, low in the recent geologic past, high in the near future, has led to plants shifting their trait levels on the LES towards faster traits. We asked whether adjustments of physiological traits could underpin faster growth from low to high CO2 and how these responses varied among plant functional types. We analysed the trait response of seedlings of up to 28 C3 plant species grown at low (160ppm), near-ambient (450ppm), and high (750ppm) CO2. We measured growth, specific leaf area (SLA), leaf gas exchange, chemical composition and stomatal traits. On average photosynthesis was reduced by 59% at low CO2 and increased by 14% at high CO2 compared to ambient CO2. Respiration decreased by 21% at low CO2 and increased by 39% at high CO2. Nitrogen content (N) per mass increased by 50% at low CO2 and decreased by 9% at high CO2. Plants drastically increased SLA at low CO2 so that despite lower carbon gain per area, carbon gain per unit mass was not reduced as much. Contrary to the responses to other resources, plant traits along the LES are adjusted towards the “fast” end of the spectrum (higher SLA, higher N) at low CO2 and towards the “slow” end (lower SLA, lower N) with increasing CO2. For a limited number of species photosynthesis per unit mass showed the same, increase at low CO2. From a resource economics perspective plants thus adjust the cost for growth towards the availability of carbon and the rate of assimilation: at lower CO2 the carbon costs decrease due to decreased respiration and lower leaf mass per area (higher SLA thinner leaves). At higher CO2 the carbon costs increase due to increased respiration and higher leaf mass per area (lower SLA thicker leaves). This suggests that CO2 increases from the past to the future are allowing plant species globally to combine faster growth with more robust, resource conservative leaves.