Plasticity, geographic variation and trait coordination in blue oak drought physiology

Plants modify their functional traits in response to changing environmental conditions under climate change. However, it remains unclear whether tree planting alters patterns and acclimation of hydraulic traits across spatial scales. Here, we compiled a site‐level data set of hydraulic traits in natural (NF) and planted forests (PF) to examine trait patterns and relationships, quantified environmental and ecological drivers on ecosystem‐scale hydraulic traits of PF and NF across China, and computationally projected future trait acclimation using the space‐for‐time approach. We identified distinct differences in hydraulic traits between NF and PF, with PF exhibiting higher hydraulic safety but lower hydraulic efficiency than NF at the species level. NF demonstrated a trade‐off between hydraulic efficiency and safety, whereas PF exhibited a contrasting positive correlation between these traits. We confirmed that both environmental and ecological factors influence ecosystem‐scale hydraulic traits in NF and PF, although dominant drivers vary among specific traits. Projections under future climate scenarios suggest that, despite persistent differences in trait acclimation between NF and PF, both forest types tend to exhibit increased water‐use efficiency and enhanced drought resistance in response to rising precipitation and air dryness. These findings provide a valuable benchmark for estimating potential changes in hydraulic traits under climate change, supporting improved simulations of carbon and water fluxes in response to climate and anthropogenic influences.

Ungulate herbivory is a key driver of leaf trait syndromes and defense strategies at the ecological and macroevolutionary levels. Herbivory should also cause short‐term evolution within plant populations, but few studies have experimentally tested this prediction. We set out to experimentally assess the plastic and heritable effects of contemporary history of ungulate herbivory on 1) leaf trait syndromes at the intraspecific level, and on the defense traits, 2) leaf size and 3) size of spines. We measured leaf traits (specific leaf area, leaf dry matter content, leaf nitrogen concentration and leaf mechanical resistance) in populations of six grass and four woody legume species that had grown under contrasting pressures of domestic ungulate herbivory for at least 40 years. We then performed a common garden experiment, measuring the same traits. Next, we performed cutting experiments on the plants grown in the common garden to measure leaf trait plasticity. In the woody species, we also measured the length of spines and the leaf size (average area per leaf), in the field and in the common garden experiment. We found that in grasses field herbivory over decades produced a displacement toward more acquisitive leaf trait syndromes. Most of these changes appeared largely due to plasticity. In woody legume species, in contrast, herbivory produced a displacement towards more conservative leaves, longer spines and smaller leaves, with the trait differences between histories of herbivory being mostly hereditary. These results point out that vertebrate herbivory can lead to evolutionary processes at contemporary time scales even in long‐lived perennial plant species, but the direction of such change depends on the life form of the species. These divergent effects could depend on the predominant anti‐herbivore strategies in the different life forms (tolerance versus resistance).

Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO2 m-2 s-1) and higher average stomatal conductance (0.18 mol H2O m-2 s-1) than their field counterparts (3.0 μmol CO2 m-2 s-1, and 0.13 mol H2O m-2 s-1 respectively). Foliar δ13C of most common-garden plants was similar among sites of origin with an average value of -26.9‰. In contrast, mean values of foliar δ13C in field plants increased substantially from -29.5‰ at low elevation to -24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211-308 g m-2 for common garden versus 107-407 g m-2 for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m-2 to 2.4 g m-2 and from 0.8 g m-2 to 2.5 g m-2 in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO2 assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.

Water scarcity is the main selective pressure determining the performance of Mediterranean plant populations, with climate change predicted to increase the intensity and duration of droughts. However, drought rarely acts in isolation. Climate change also involves substantial warming in this region and may disrupt natural processes, including biotic interactions. Phenotypic plasticity allows plants to cope with rapid and multifaceted environmental changes. Although our knowledge of plastic responses to drought in Mediterranean plants has increased in recent years, how co-occurring simultaneous stressors interact to produce additive, synergistic, or antagonistic effects that enhance or constrain adaptive plastic responses to drought is still unknown. Using a factorial experimental approach based on a multivariate common garden, we assessed whether adaptive phenotypic plasticity to drought and population differentiation in traits related to drought response were affected by the occurrence of other key simultaneous stressors, warming and intraspecific competition, in a Mediterranean gypsum endemic shrub. In response to drought, plants expressed adaptive plastic responses associated with a mixed resource-use strategy, combining conservative (sclerophyllous leaves with higher water use efficiency) and acquisitive (advanced phenology) phenotypic responses. Although the response to drought was modified by synergistic and antagonistic interactions with warming and competition, these interactions did not change the direction or reduce the extent of adaptive plasticity to drought. This suggests that plastic responses to drought may also provide benefits against warming and competition. Finally, we detected significant population differentiation in all functional traits, but phenotypic differences in reproductive biomass were significantly reduced under combined drought and warming. Our results emphasize the robustness of adaptive plasticity to drought under complex stress scenarios and underscore the importance of realistic, multifactorial experimental approaches to predict whether adaptive responses of plant populations will remain effective in a climate change context and influence their future ecological and evolutionary dynamics.

Key message Evergreen and deciduous species in a subtropical urban forest of Eastern China exhibit pronounced differences in leaf traits, with evergreens species showing lower photosynthetic rate on a leaf mass basis and leaf nutrient contents, but higher leaf mass per area ratio, leaf thickness, leaf carbon content, and leaf carbon-to-nitrogen ratio, whereas deciduous species show the opposite pattern, reflecting distinct resource-use characteristics. In addition, leaf economic and hydraulic traits are coordinated, with higher vein density associated with higher scores along the leaf economics spectrum PCA axis, reflecting resource-acquisitive characteristics and highlighting vein density as a key trait linking water transport capacity to carbon economy. Context Understanding how leaf economics and hydraulic traits vary and interact among different plant growth forms and leaf habits is essential for elucidating plant adaptability. However, the coupling of these two trait dimensions remains unclear within urban forest ecosystems where environmental conditions differ significantly from natural forests. Aims This study aimed to investigate variation and coordination between leaf economics and hydraulic traits among woody species in a subtropical urban forest of Eastern China, focusing on differences between leaf habits and growth forms. Methods We measured 10 leaf economic traits and 4 hydraulic traits across 53 woody species from a subtropical urban forest. Results Evergreen species exhibited lower photosynthetic rate on a leaf mass basis, leaf nutrient contents, and higher leaf mass per area ratio, leaf thickness, leaf carbon content, and leaf carbon-to-nitrogen ratio, consistent with resource-conserving characteristics. Deciduous species showed higher values of these parameters, indicative of rapid resource acquisition. Shrubs displayed significantly higher phosphorous content in leaves than trees. Vein density was positively correlated with the leaf economic spectrum. Conclusion These findings reveal a coordination between leaf hydraulic and economic traits. This coupling highlights the balance between water transport and resource acquisition characteristics.

The hydraulic traits of a plant species may reflect its climate adaptations. Southwest China is considered as a biodiversity hotpot of the genus Quercus (oak). However, the hydraulic adaptations of Asian oaks to their climate niches remain unclear. Ten common garden-grown oak species with distinct natural distributions in eastern Asia were used to determine their stem xylem embolism resistance (water potential at 50% loss of hydraulic conductivity, P50), stem hydraulic efficiency (vessel anatomy and sapwood specific hydraulic conductivity (Ks)) and leaf anatomical traits. We also compiled four key functional traits: wood density, hydraulic-weighted vessel diameter, Ks and P50 data for 31 oak species from previous literature. We analyzed the relationship between hydraulic traits and climatic factors over the native ranges of 41 oak species. Our results revealed that the 10 Asian oak species, which are mainly distributed in humid subtropical habitats, possessed a stem xylem with low embolism resistance and moderate hydraulic efficiency. The deciduous and evergreen species of the 10 Asian oaks differed in the stem and leaf traits related to hydraulic efficiency. Ks differed significantly between the two phenological groups (deciduous and evergreens) in the 41-oak dataset. No significant difference in P50 between the two groups was found for the 10 Asian oaks or the 41-oak dataset. The oak species that can distribute in arid habitats possessed a stem xylem with high embolism resistance. Ks negatively related to the humidity of the native range of the 10 Asian oaks, but showed no trend when assessing the entire global oak dataset. Our study suggests that stem hydraulic conductivity and embolism resistance in Quercus species are shaped by their climate niche. Our findings assist predictions of oak drought resistance with future climate changes for oak forest management.

Multi-dimensional trait mechanisms underlying community assembly at regional scales are largely unclear. In this study, we measured leaf economic, hydraulic and anatomical traits of 394 tree species from tropical to cold temperate forests, from which we calculated the leaf trait moments (mean, variance, skewness, and kurtosis) using community-weighted methods. Economic and hydraulic traits were decoupled at the species level, but coupled at the community level, and relationships between leaf traits in observed communities were stronger than that in null communities, suggesting that the adaptive mechanisms of plant species may be different. Furthermore, leaf economic traits were distributed more evenly across species occupying communities with lower temperature and precipitation, whereas hydraulic traits were distributed more evenly under lower water availability. This suggests that limiting similarity of specific leaf traits within communities would be enhanced when related-resources are limited, and highlights the independent assembly of leaf economics and hydraulic traits in terms of functional evenness. Importantly, the moments of leaf economic and hydraulic traits of observed communities explained more variation in ecosystem productivity than that of null communities, indicating ecosystem productivity depended on trait-based community assembly. Our results highlight the principles of community assembly regarding multi-dimensionsional traits in natural forests at a regional scale.

Introduced species, which establish in novel environments, provide an opportunity to explore trait evolution and how it may contribute to the distribution and spread of species. Here, we explore trait changes of the perennial herb Lupinus polyphyllus based on 11 native populations in the western USA and 17 introduced populations in Finland. More specifically, we investigated whether introduced populations outperformed native populations in traits measured in situ (seed mass) and under common garden conditions during their first year (plant size, flowering probability, and number of flowering shoots). We also explored whether climate of origin (temperature) influenced plant traits and quantified the degree to which trait variability was explained collectively by country and temperature as compared to other population‐level differences. Three out of four plant traits differed between the native and introduced populations; only seed mass was similar between countries, with most of its variation attributed to other sources of intraspecific variation not accounted for by country and temperature. Under common garden conditions, plants originating from introduced populations were larger than those originating from native populations. However, plants from the introduced range flowered less frequently and had fewer flowering shoots than their native‐range counterparts. Temperature of a population's origin influenced plant size in the common garden, with plant size increasing with increasing mean annual temperature in both native and introduced populations. Our results of the first year reveal genetic basis for phenotypic differences in some fitness‐related traits between the native and introduced populations of L. polyphyllus. However, not all of these trait differences necessarily contribute to the invasion success of the species and thus may not be adaptive, which raises a question how persistent the trait differences observed in the first year are later in individuals’ life for perennial herbs.

Models of tree function and forest ecosystem carbon budgets often assume that potential global changes in temperature and/or other factors may alter tissue nitrogen (N) and dark respiration rates (R d ). However, little is known of patterns of co-variation in tissue N and R d among intraspecific populations originating along climatic gradients, and of whether an N-based model of R d can link these two variables. To address these issues, we studied N and R d in fully expanded needles of 10-year-old trees of 14 Scots Pine (Pinus sylvestris) populations of wide-ranging origin (43 ° to 60 °N), grown under common garden conditions. For 11 lowland populations (elevation < 200 m) from the contiguous part of the species range (48 ° to 60°N) grown at a field site in Kornik, western Poland (52 °N), there were greater needle %N in populations from increasing latitude of origin or decreasing mean annual temperature (r≥0.93, P<0.01). Similar %N and latitude of origin correlations were observed in another year at this site and in retrospective analyses of published data for different sets of Scots Pine populations grown in common gardens at 48°, 52 °C and 62 °N latitudes. Needle R d rates of the 11 lowland populations growing at Kornik and measured at a common temperature (20 °C) were greater, by as much as 50%, for more northerly than southerly populations. Mean R d rates were positively correlated to latitude of origin and to mean annual temperature (P < 0.05, r = 0.7 to 0 8). R d and needle %N were positively correlated (P<0.01, r=0.75), with one relationship fitting all data. Across the entire range from 1.15 to to 1.55 needle %N, R d increased from 4.5 to to 6.9 nmol g -1 s -1 . Mean needle %N and R d values for two montane southern populations (43 ° and 44 °N, elevation ≥ 885 m) growing in the same common garden at Kornik were consistent with the relationships between mean annual temperature, needle %N and R d observed for the more northerly populations but did not fit the latitudinal patterns. This suggests that temperature and/or associated climate variables are likely the driving force for observed genetic variation in Scots Pine needle %N and R d across latitudinal and altitudinal gradients. Results of these common garden studies support the idea of a general relationship between needle dark respiration and N concentration, and indicate that there is intraspecific genetic variation in physiology that is selected by climate that persists in a common environment, resulting in higher needle %N and respiration in plants originating from colder habitats. Such patterns need to be better understood and quantified, and merit consideration in modelling of current and potential global change effects on plant function and global carbon cycles.

Oaks (genus Quercus) often display a large range of phenotypic variation across many of their traits. The contribution of genetic and environmental sources, and their interaction, to this variation can be partitioned experimentally using common garden plantings in which several genotypes are grown in a single location and the phenotype of interest is measured. Due to their slow growth and complex genetic structure, oaks have rarely been grown to maturity in experimental conditions that would allow partitioning phenotypic variation in this traditional way. Here we present results from trees growing in two established experimental gardens of Quercus douglasii Hook. & Arn. planted in 1991. Data from these common gardens are combined with additional data collected at the original provenance populations that served as acorn source locations. We surveyed phenological progression through the spring at both garden and field sites and found significant associations between fall and spring minimum temperatures and spring phenology, represented here as the date of bud break. A genetic component of phenological variation associated with the provenance sites was identified at both common gardens and accounts for 16.4% of the total variation observed among trees, while 68.2% of the variation can be attributed to environmental plasticity, plus a genetic × environmental interaction that accounts for about 1% of bud break variation. We discuss the implications of these components of phenological variation in Blue Oak, especially with respect to climate change, local adaptation, restoration, and assisted gene flow.

Summary1. Glacial history has affected the phylogeographic structure of numerous Alpine plant species, but its impact on phenotypic differentiation has been little studied. Therefore, we asked whether phenotypic differentiation in a common garden reflects the phylogeographic structure of the widespread Alpine plant Geum reptans L.2. We combined a molecular investigation with a common garden experiment and investigated genets from 16 populations of G. reptans sampled from the European Alps. Using neutral molecular markers (RAPDs) and Bayesian cluster analysis, we analysed the species’ genetic differentiation and phylogeographic structure. In the common garden, we measured the differentiation of phenotypic traits related to growth, reproduction and leaf morphology.3. Molecular analysis partitioned the populations into three genetic groups, indicating pronounced phylogeographic structure. Regional molecular variation was correlated with regional phenotypic differentiation.4. Quantitative trait differentiation (QST) differed from neutral molecular differentiation (GST) in 10 of 11 traits, indicating that selection has contributed to phenotypic differentiation. Significant negative correlations between biomass and precipitation records for site of origin are a further indication of adaptation.5. Synthesis. The current study compared regional molecular variation and phenotypic differentiation among populations of a widespread species in the context of extreme range changes during glaciations in the Alps. Because the common garden phenotypic differentiation of G. reptans reflects its phylogeographic structure, we conclude that glacial history affected both genotypes and phenotypes. The results suggest that the present‐day phenotypic differentiation was caused by genetic drift and limited gene flow between populations in glacial refugia and during post‐glacial recolonization, as well as by adaptation to current climatic conditions. Our findings are relevant for understanding the adaptive potential of Alpine plants and predicting potential range shifts in response to future climate change.

Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber.Highly significant variation among clones was found in almost all parameters. In the common garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground parameters and parameters of the rhizome system were strongly affected by red/far red ratio; among‐clone variation was also almost always significant. The genotype × environment interaction was significant for tillering rate and rhizome architecture. The structure of the rhizome system (which is the major component of clonal spread in space) is a complex result of several components whose inter‐clone variations differ: (i) genetically determined mean rhizome system size, (ii) overall plasticity in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome architecture. Because of the variation in plasticity in rhizome architecture, some c lones seemed to possess the ability to exploit a favourable habitat patch by producing short branches when there; whereas the remaining clones appeared to possess only a simple escape mechanism from unfavourable patches.Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. rubra are sufficient to make genets experience different patches in their lifetime. The high variation in both genotype means and plasticities is likely to be due to selection early in genet life in an environment which is heterogeneous at a fine scale.

The potential to use differences in traits of white clover (Trifolium repens L.) varieties to improve mature yield of winter wheat or winter oilseed rape (Brassica napus L.) sown in white clover living mulch was studied in two field experiments conducted in Southern Sweden. The clover varieties Sonja, S184 and AberCrest, differing in leaf size and winter hardiness, were undersown in spring barley. Three consecutive crops of winter wheat or one crop of winter rape sown at two densities followed the barley. In the first year, the mature yields of wheat and high density rape equalled yields without white clover when AberCrest was used, while Sonja reduced the wheat yield by one third and the rape yield to nothing. S184 was intermediate. White clover increased yields by 14–19% in the second wheat crop, but had no effect in the weed infested third wheat crop. The average amount of white clover at flowering of wheat was always largest with Sonja, which increased its biomass earlier in spring than AberCrest. It was concluded that white clover traits are important when developing the intercropping system for large mature yields, especially when herbicides are avoided.

Evolutionary biologists are largely polarized in their approaches to integrating microevolutionary and macroevolutionary processes. Neo-Darwinians typically seek to identify population-level selective and genetic processes that culminate in macroevolutionary events. Epigeneticists and structuralists, on the other hand, emphasize developmental constraints on the action of natural selection, and highlight the role of epigenetic shifts in producing evolutionary change in morphology. Accordingly, the ways in which these paradigms view and address morphological contrasts between classes of related organisms differ. These paradigms, although seldomly explicitly stated, emerge in paleoanthropology as well. Considerations of postcranial morphological contrasts between archaic and modern humans typically fall into one of two broad interpretive models. The first derives from the neo-Darwinian perspective and holds that evolution in the postcranial skeleton was largely mosaic (operating in a particulate manner), and that temporal change in specific traits informs us about behavioral shifts or genetic evolution affecting isolated anatomical regions (i.e., adaptive behavioral inferences can be made from comparative studies of individual trait complexes). The alternative model follows from the epigeneticist paradigm and sees change in specific postcranial traits as correlated responses to change in overall body form (involving shifts in regulation of skeletal growth, or selective and developmental responses to broad adaptive shifts). By this view, integration of functional systems both constrains and directs evolution of various traits, and morphological contrasts inform us about overall change in body form related to change in such things as overall growth patterns, climatic adaptation, and technological dependency. These models were tested by confirmatory factor analysis using measures of upper body form and upper limb morphological traits in Eurasian Neandertal and early modern fossils and recent human samples. Results indicate (1) a model of morphological integration fits the data better than a model of no integration, but (2) this integration accounts for less than half of the variance in upper limb traits, suggesting a high degree of tolerance for particulate evolution in the context of an integrated upper body plan. Significant relationships were detected between joint shapes and body size, between humeral shaft shape and body size and chest shape, and between measures of biomechanical efficiency and robusticity. The observed morphological differences between late archaic and early modern humans reflect particulate evolution in the context of constraints imposed by genetic and morphological integration. While particulate approaches to interpreting the fossil record appear to be justified, attention must also be paid to delineating the nature and extent of morphological integration and its role in both constraining and producing observed patterns of variation between groups. Confirmatory factor analysis provides a means of examining trait covariance matrices, and serves as a useful method of identifying patterns of integration in morphology. © 1996 Wiley-Liss, Inc.

Aim of study: We aimed at identifying differences in the response to water shortage between Eucalyptus globulus clones. Area of study: Field trials were established in SW Spain. Material and methods: Potted plants from six clones were grown in a greenhouse for 35 days under two watering regimes. Two clones were F0 genotypes and the other four were F1 (hybrid) genotypes, including one inbred clone. Differences in stomatal conductance, hydraulic traits, growth and specific leaf area (SLA) were analyzed. Main results: Water shortage decreased SLA, growth in height and leaf area and leaf-specific hydraulic conductivity (KLmax). We measured the highest growth in F1 genotypes and the lowest in the clone in which SLA was lowest. The inbred clone showed the highest growth reduction under water shortage. There was substantial hysteresis between leaf water potential (Y) and native embolism, most probably a result of combined cavitation and refilling. High losses of hydraulic conductance were compatible with high stomatal conductances. Maximum values of stomatal conductance decreased with the soil water content estimated from predawn Y and were lowest in the inbred clone, showing less plasticity and a diminished ability to cope with high temperatures, which could explain its poor development under field conditions. Research highlights: Soil water content and predawn Y appeared as critical factors controlling stomata closure, while stomatal conductance and SLA could be useful to predict differences in growth and survival from early trials.