Deciduous and evergreen oaks show contrasting adaptive responses in leaf mass per area across environments

Rising Temperatures, Falling Leaves: Predicting the Fate of Cyprus's Endemic Oak under Climate and Land Use Change

Endemic island species face heightened extinction risk from climate-driven shifts, yet standard models often underestimate threat levels for those like Quercus alnifolia, an iconic Cypriot oak with pre-adaptations to aridity. Through species distribution modelling, we investigated the potential shifts in its distribution under future climate and land-use change scenarios. Our approach uniquely combines dispersal constraints, detailed soil characteristics, hydrological factors, and anticipated soil erosion data, offering a comprehensive assessment of environmental suitability. We quantified the species' sensitivity, exposure, and vulnerability to projected changes, conducting a preliminary IUCN extinction risk assessment according to Criteria A and B. Our projections uniformly predict range reductions, with a median decrease of 67.8% by the 2070s under the most extreme scenarios. Additionally, our research indicates Quercus alnifolia's resilience to diverse erosion conditions and preference for relatively dry climates within a specific annual temperature range. The preliminary IUCN risk assessment designates Quercus alnifolia as Critically Endangered in the future, highlighting the need for focused conservation efforts. Climate and land-use changes are critical threats to the species' survival, emphasising the importance of comprehensive modelling techniques and the urgent requirement for dedicated conservation measures to safeguard this iconic species.

Drought mitigates the adverse effects of O3 on plant photosynthesis rather than growth: A global meta-analysis considering plant functional types

Tropospheric ozone (O3 ) is a phytotoxic air pollutant adversely affecting plant growth. High O3 exposures are often concurrent with summer drought. The effects of both stresses on plants are complex, and their interactions are not yet well understood. Here, we investigate whether drought can mitigate the negative effects of O3 on plant physiology and growth based on a meta-analysis. We found that drought mitigated the negative effects of O3 on plant photosynthesis, but the modification of the O3 effect on the whole-plant biomass by drought was not significant. This is explained by a compensatory response of water-deficient plants that leads to increased metabolic costs. Relative to water control condition, reduced water treatment decreased the effects of O3 on photosynthetic traits, and leaf and root biomass in deciduous broadleaf species, while all traits in evergreen coniferous species showed no significant response. This suggested that the mitigating effects of drought on the negative impacts of O3 on the deciduous broadleaf species were more extensive than on the evergreen coniferous ones. Therefore, to avoid over- or underestimations when assessing the impact of O3 on vegetation growth, soil moisture should be considered. These results contribute to a better understanding of terrestrial ecosystem responses under global change.

Leaf habit and plant architecture integrate whole-plant economics and contextualize trait-climate associations within ecologically diverse genus Rhododendron

Plant resource strategies negotiate a trade-off between fast growth and stress resistance, characterized by specific leaf area (SLA). How SLA relates to leaf structure and function or plant climate associations remains open for debate, and leaf habit and plant architecture may alter the costs versus benefits of individual traits. We used phylogenetic canonical correspondence analysis and phylogenetic least squares to understand the relationship of anatomy and gas exchange to published data on root, wood, architectural and leaf economics traits and climate. Leaf anatomy was structured by leaf habit and carbon to nitrogen ratio was a better predictor of gas exchange than SLA. We found significant correspondence of leaf anatomy with branch architecture and wood traits, gas exchange corresponded with climate, while leaf economics corresponded with climate, architecture, wood and root traits. Species from the most seasonal climates had the highest trait-climate correspondence, and different aspects of economics and anatomy reflected leaf carbon uptake versus water use. Our study using phylogenetic comparative methods including plant architecture and leaf habit provides insight into the mechanism of whole-plant functional coordination and contextualizes individual traits in relation to climate, demonstrating the evolutionary and ecological relevance of trait-trait correlations within a genus with high biodiversity.

Photochemical attributes determine the responses of plant species from different functional groups of ferruginous outcrops when grown in iron mining substrates

Environments originating from banded iron formations, such as the canga , are important reference ecosystems for the recovery of degraded areas by mining. The objective of this work was to evaluate if the relationship between morphofunctional and photosynthetic attributes of native canga species from different functional group results in distinct responses when grown in iron mining tailings substrate. The experiment was carried out with species belonging to different functional groups: a widespread semi-deciduous tree-shrub, Myrcia splendens ; an endemic deciduous shrub, Jacaranda caroba ; and a nitrogen-fixing herbaceous species, Periandra mediterranea . The species were grown in two conditions, reference soil and iron ore tailing. Despite belonging to different functional groups when grown in tailings, the morphofunctional attributes presented similar responses between species. M. splendens was the species most affected by the conditions imposed by the iron ore mining tailings, with decreased light-use efficiency and electron transport. P. mediterranea had satisfactory growth and maintenance of photosynthetic attributes. J. caroba growing in the tailings increased the effective quantum yield of PSII. The photochemical and growth assessments were able to better explain the adaptive strategies developed by the species, guaranteeing a greater chance of success during the rehabilitation of mining substrates.

Plasticity of mesophyll cell density and cell wall thickness and composition play a pivotal role in regulating plant growth and photosynthesis under shading in rapeseed

BACKGROUND AND AIMS

Plasticity of leaf growth and photosynthesis is an important strategy of plants to adapt to shading stress; however, their strategy of leaf development to achieve a simultaneous increase in leaf area and photosynthesis under shading remains unknown.

METHODS

In the present study, a pot experiment was conducted using three rapeseed genotypes of Huayouza 50 (HYZ50), Zhongshuang 11 (ZS11) and Huayouza 62 (HYZ62), and the responses of plant growth, leaf morphoanatomical traits, cell wall composition and photosynthesis to shading were investigated.

KEY RESULTS

Shading significantly increased leaf area per plant (LAplant) in all genotypes, but the increase in HYZ62 was greater than that in HYZ50 and ZS11. The greater increment of LAplant in HYZ62 was related to the larger decrease in leaf mass per area (LMA) and leaf density (LD), which were in turn related to less densely packed mesophyll cells and thinner cell walls (Tcw). Moreover, shading significantly increased photosynthesis in HYZ62 but significantly decreased it in HYZ50. The enhanced photosynthesis in HYZ62 was related to increased mesophyll conductance (gm) due primarily to thinner cell walls.

CONCLUSIONS

The data presented indicate that the different plasticity of mesophyll cell density, cell wall thickness and cell wall composition in response to shading can dramatically affect leaf growth and photosynthesis.

Climate change impacts the distribution of Quercus section Cyclobalanopsis (Fagaceae), a keystone lineage in East Asian evergreen broadleaved forests

East Asian evergreen broadleaved forests (EBFLs) harbor high species richness, but these ecosystems are severely impacted by global climate change and deforestation. Conserving and managing EBLFs requires understanding dominant tree distribution dynamics. In this study, we used 29 species in Quercus section Cyclobalanopsis-a keystone lineage in East Asian EBLFs-as proxies to predict EBLF distribution dynamics using species distribution models (SDMs). We examined climatic niche overlap, similarity, and equivalency among seven biogeographical regions' species using 'ecospat'. We also estimated the effectiveness of protected areas in the predicted range to elucidate priority conservation regions. Our results showed that the climatic niches of most geographical groups differ. The western species under the Indian summer monsoon regime were mainly impacted by temperature factors, whereas precipitation impacted the eastern species under the East Asian summer monsoon regime. Our simulation predicted a northward range expansion of section Cyclobalanopsis between 2081 and 2100, except for the ranges of the three Himalayan species analyzed, which might shrink significantly. The greatest shift of highly suitable areas was predicted for the species in the South Pacific, with a centroid shift of over 300 km. Remarkably, only 7.56% of suitable habitat is currently inside protected areas, and the percentage is predicted to continue declining in the future. To better conserve Asian EBLFs, establishing nature reserves in their northern distribution ranges, and transplanting the populations with predicted decreasing numbers and degraded habitats to their future highly suitable areas, should be high-priority objectives.

Foliar Phenotypic Plasticity Reflects Adaptation to Environmental Variability

Arabidopsis thaliana ecotypes adapted to native habitats with different daylengths, temperatures, and precipitation were grown experimentally under seven combinations of light intensity and leaf temperature to assess their acclimatory phenotypic plasticity in foliar structure and function. There were no differences among ecotypes when plants developed under moderate conditions of 400 µmol photons m-2 s-1 and 25 °C. However, in response to more extreme light or temperature regimes, ecotypes that evolved in habitats with pronounced differences in either the magnitude of changes in daylength or temperature or in precipitation level exhibited pronounced adjustments in photosynthesis and transpiration, as well as anatomical traits supporting these functions. Specifically, when grown under extremes of light intensity (100 versus 1000 µmol photons m-2 s-1) or temperature (8 °C versus 35 °C), ecotypes from sites with the greatest range of daylengths and temperature over the growing season exhibited the greatest differences in functional and structural features related to photosynthesis (light- and CO2-saturated capacity of oxygen evolution, leaf dry mass per area or thickness, phloem cells per minor vein, and water-use efficiency of CO2 uptake). On the other hand, the ecotype from the habitat with the lowest precipitation showed the greatest plasticity in features related to water transport and loss (vein density, ratio of water to sugar conduits in foliar minor veins, and transpiration rate). Despite these differences, common structure-function relationships existed across all ecotypes and growth conditions, with significant positive, linear correlations (i) between photosynthetic capacity (ranging from 10 to 110 µmol O2 m-2 s-1) and leaf dry mass per area (from 10 to 75 g m-2), leaf thickness (from 170 to 500 µm), and carbohydrate-export infrastructure (from 6 to 14 sieve elements per minor vein, from 2.5 to 8 µm2 cross-sectional area per sieve element, and from 16 to 82 µm2 cross-sectional area of sieve elements per minor vein); (ii) between transpiration rate (from 1 to 17 mmol H2O m-2 s-1) and water-transport infrastructure (from 3.5 to 8 tracheary elements per minor vein, from 13.5 to 28 µm2 cross-sectional area per tracheary element, and from 55 to 200 µm2 cross-sectional area of tracheary elements per minor vein); (iii) between the ratio of transpirational water loss to CO2 fixation (from 0.2 to 0.7 mol H2O to mmol-1 CO2) and the ratio of water to sugar conduits in minor veins (from 0.4 to 1.1 tracheary to sieve elements, from 4 to 6 µm2 cross-sectional area of tracheary to sieve elements, and from 2 to 6 µm2 cross-sectional area of tracheary elements to sieve elements per minor vein); (iv) between sugar conduits and sugar-loading cells; and (v) between water conducting and sugar conducting cells. Additionally, the proportion of water conduits to sugar conduits was greater for all ecotypes grown experimentally under warm-to-hot versus cold temperature. Thus, developmental acclimation to the growth environment included ecotype-dependent foliar structural and functional adjustments resulting in multiple common structural and functional relationships.

Disentangling leaf structural and material properties in relationship to their anatomical and chemical compositional traits in oaks (Quercus L.)

BACKGROUND AND AIMS

The existence of sclerophyllous plants has been considered an adaptive strategy against different environmental stresses. Given that it literally means 'hard-leaved', it is essential to quantify the leaf mechanical properties to understand sclerophylly. However, the relative importance of each leaf trait for mechanical properties is not yet well established.

METHODS

Genus Quercus is an excellent system to shed light on this because it minimizes phylogenetic variation while having a wide variation in sclerophylly. We measured leaf anatomical traits and cell wall composition, analysing their relationship with leaf mass per area and leaf mechanical properties in a set of 25 oak species.

KEY RESULTS

The upper epidermis outer wall makes a strong and direct contribution to the leaf mechanical strength. Moreover, cellulose plays a crucial role in increasing leaf strength and toughness. The principal component analysis plot based on leaf trait values clearly separates Quercus species into two groups corresponding to evergreen and deciduous species.

CONCLUSIONS

Sclerophyllous Quercus species are tougher and stronger owing to their thicker epidermis outer wall and/or higher cellulose concentration. Furthermore, section Ilex species share common traits, although they occupy different climates. In addition, evergreen species living in mediterranean-type climates share common leaf traits irrespective of their different phylogenetic origin.

Genomic data and common garden experiments reveal climate-driven selection on ecophysiological traits in two Mediterranean oaks

Improving our knowledge of how past climate-driven selection has acted on present-day trait population divergence is essential to understand local adaptation processes and improve our predictions of evolutionary trajectories in the face of altered selection pressures resulting from climate change. In this study, we investigated signals of selection on traits related to drought tolerance and growth rates in two Mediterranean oak species (Quercus faginea and Q. lusitanica) with contrasting distribution ranges and climatic niches. We genotyped 182 individuals from 24 natural populations of the two species using restriction-site-associated DNA sequencing and conducted a thorough functional characterization in 1602 seedlings from 21 populations cultivated in common garden experiments under contrasting watering treatments. Our genomic data revealed that both Q. faginea and Q. lusitanica have very weak population genetic structure, probably as a result of high rates of pollen-mediated gene flow among populations and large effective population sizes. In contrast, common garden experiments showed evidence of climate-driven divergent selection among populations on traits related to leaf morphology, physiology and growth in both species. Overall, our study suggests that climate is an important selective factor for Mediterranean oaks and that ecophysiological traits have evolved in drought-prone environments even in a context of very high rates of gene flow among populations.

Phylogenomic insights into the origin and evolutionary history of evergreen broadleaved forests in East Asia under Cenozoic climate change

The evergreen versus deciduous leaf habit is an important functional trait for adaptation of forest trees and has been hypothesized to be related to the evolutionary processes of the component species under paleoclimatic change, and potentially reflected in the dynamic history of evergreen broadleaved forests (EBLFs) in East Asia. However, knowledge about the shift of evergreen versus deciduous leaf with the impact of paleoclimatic change using genomic data remains rare. Here, we focus on the Litsea complex (Lauraceae), a key lineage with dominant species of EBLFs, to gain insights into how evergreen versus deciduous trait shifted, providing insights into the origin and historical dynamics of EBLFs in East Asia under Cenozoic climate change. We reconstructed a robust phylogeny of the Litsea complex using genome-wide single-nucleotide variants (SNVs) with eight clades resolved. Fossil-calibrated analyses, diversification rate shifts, ancestral habit, ecological niche modelling and climate niche reconstruction were employed to estimate its origin and diversification pattern. Taking into account studies on other plant lineages dominating EBLFs of East Asia, it was revealed that the prototype of EBLFs in East Asia probably emerged in the Early Eocene (55-50 million years ago [Ma]), facilitated by the greenhouse warming. As a response to the cooling and drying climate in the Middle to Late Eocene (48-38 Ma), deciduous habits were evolved in the dominant lineages of the EBLFs in East Asia. Up to the Early Miocene (23 Ma), the prevailing of East Asian monsoon increased the extreme seasonal precipitation and accelerated the emergence of evergreen habits of the dominant lineages, and ultimately shaped the vegetation resembling that of today.

Stem hydraulic conductivity and embolism resistance of Quercus species are associated with their climatic niche

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.

Leaf economics fundamentals explained by optimality principles

The life span of leaves increases with their mass per unit area (LMA). It is unclear why. Here, we show that this empirical generalization (the foundation of the worldwide leaf economics spectrum) is a consequence of natural selection, maximizing average net carbon gain over the leaf life cycle. Analyzing two large leaf trait datasets, we show that evergreen and deciduous species with diverse construction costs (assumed proportional to LMA) are selected by light, temperature, and growing-season length in different, but predictable, ways. We quantitatively explain the observed divergent latitudinal trends in evergreen and deciduous LMA and show how local distributions of LMA arise by selection under different environmental conditions acting on the species pool. These results illustrate how optimality principles can underpin a new theory for plant geography and terrestrial carbon dynamics.

Leaf wettability, anatomy and ultra-structure of Nothofagus antarctica and N. betuloides grown under a CO2 enriched atmosphere

Increasing CO₂ air concentration may affect wettability, anatomy and ultra-structure of leaves of Patagonian forest species, evergreen and deciduous plants potentially responding differently to such CO₂ increases. In this study, we analysed the wettability, anatomy and ultra-structure of leaves of Nothofagus antarctica (deciduous) and N. betuloides (evergreen) grown under high CO₂ concentrations. Leaf wettability was affected by increasing CO₂, in different directions depending on species and leaf side. In both species, soluble cuticular lipid concentrations per unit leaf area raised with higher CO₂ levels. Stomatal parameters (density, size of guard cells and pores) showed different responses to CO₂ increasing depending on the species examined. In both species, leaf tissues showed a general trend to diminish with higher CO₂ concentration. Cuticle thickness was modified with higher CO₂ concentration in N. betuloides, but not in N. antarctica leaves. In both species, chloroplasts were often damaged with the increase in CO₂ concentration. Our results show that several surface and internal leaf parameters can be modified in association with an increase in atmospheric CO₂ concentration which may very among plant species.

Germplasm Resources of Oaks (Quercus L.) in China: Utilization and Prospects

Oaks exhibit unique biological characteristics and high adaptability to complex climatic and soil conditions. They are widely distributed across various regions, spanning 40 degrees latitude and 75 degrees longitude. The total area of oak forest in China is 16.72 million hm². There are 60 lineages of Quercus in China, including 49 species, seven varieties, and four subgenera. Archaeological data indicate that oaks were already widely distributed in ancient times, and they are dominant trees in vast regions of China's forests. In addition, the acorn was an important food for ancestral humans, and it has accompanied human civilization since the early Paleolithic. Diverse oak species are widely distributed and have great functional value, such as for greening, carbon sequestration, industrial and medicinal uses, and insect rearing. Long-term deforestation, fire, diseases, and pests have led to a continuous decline in oak resources. This study discusses the Quercus species and their distribution in China, ecological adaptation, and the threats facing the propagation and growth of oaks in a changing world. This will give us a better understanding of Quercus resources, and provide guidance on how to protect and better utilize germplasm resources in China. The breeding of new varieties, pest control, and chemical and molecular research also need to be strengthened in future studies.

Asymmetric character displacement in mixed oak stands

Ecological character displacement (ECD) refers to a pattern of increased divergence at sites where species ranges overlap caused by competition for resources. Although ECD is believed to be common, there are few in-depth studies that clearly establish its existence, especially in plants. Thus, we have compared leaf traits in allopatric and sympatric populations of two East Asian deciduous oaks: Quercus dentata and Quercus aliena. In contrast to previous studies, we define sympatry and allopatry at a local scale, thereby comparing populations that can or cannot directly interact. Using genetic markers, we found greater genetic divergence between the two oak species growing in mixed stands and inferred that long-term gene flow has predominantly occurred asymmetrically from the cold-tolerant species (Q. dentata) to the warm-demanding later colonizing species (Q. aliena). Analysis of leaf traits revealed greater divergence in mixed than in pure oak stands. This was mostly due to the later colonizing species being characterized by more resource-conservative traits in the presence of the other species. Controlling for relevant environmental differences did not alter these conclusions. These results suggest that asymmetric trait divergence can take place where species coexist, possibly due to the imbalance in demographic history of species resulting in asymmetric inter-specific selection pressures.

Limited Acclimation in Leaf Morphology and Anatomy to Experimental Drought in Temperate Forest Species

Simple Summary

Climate change shown to have a significant impact on the forest ecosystem due to increased and more frequent occurrence of extreme drought. However, in order to successfully adjust to the xeric environments, plants can usually adopt a variety of adaptation strategies. Here, we investigated the morpho-anatomical traits and biomass allocation patterns as acclimation mechanisms in drought conditions. We found that the interrelation between leaf morphological and anatomical traits were equally affected by drought conditions across all species. This suggests that there is no convincing evidence to classify taxa based on drought resistance vs. drought tolerance. However, based on the biomass allocation pattern, we found that P. koraiensis and F. mandshurica had the higher RMF and total PB, but lower LFM, suggesting higher drought tolerance than those of the other species. Therefore, our dataset revealed some easily measurable traits, such as LMF, RMF, and PB, which demonstrated the seedling’s ability to cope with drought and which could be utilized to choose drought-tolerant species for reforestation in the temperate forest.

Abstract

Drought is a critical and increasingly common abiotic factor that has impacts on plant structures and functioning and is a challenge for the successful management of forest ecosystems. Here, we test the shifts in leaf morpho-anatomical or hydraulic traits and plant growth above ground caused by drought. A factorial experiment was conducted with two gymnosperms (Larix gmelinii and Pinus koraiensis) and two angiosperms (Fraxinus mandshurica and Tilia amurensis), tree species grown under three varying drought intensities in NE China. Considering all the species studied, the plant height (PH), root collar diameter (RCD), and plant biomass (PB) were significantly decreased by drought. The leaf thickness (LT) increased, while the leaf area (LA) decreased with drought intensity. In the gymnosperms, the mesophyll thickness (MT) increased, and the resin duct decreased, while in the angiosperms the palisade mesophyll thickness (PMT), the spongy mesophyll thickness (SMT), and the abaxial (ABE) and adaxial epidermis (ADE) thickness were increased by drought. The correlation analysis revealed that P. koraiensis and F. mandshurica had the higher RMF and total plant biomass, but the least LMF, suggesting drought tolerance. In contrast, the L. gmelinii had the least RMF and higher LMF, suggesting vulnerability to drought. Similarly, T. amurensis had the higher leaf size, which increased the evaporative demand and depleted the soil water quickly relative to the other species. The interrelation among the morpho-anatomical leaf traits was equally affected by drought across all the studied species, suggesting that there is no clear evidence to differentiate the taxa based on drought resistance vs. drought tolerance. Thus, we have identified some easily measurable traits (i.e., LMF, RMF, and PB) which evidenced the seedling’s ability to cope with drought and which therefore could be used as proxies in the selection of drought tolerant species for reforestation in the temperate forest.

Sources and consequences of mismatch between leaf disc and whole-leaf leaf mass per area (LMA)

PREMISE

Leaf mass per area (LMA), which is an important functional trait in leaf economic spectrum and plant growth analysis, is measured from leaf discs or whole leaves. Differences between the measurement methods may lead to large differences in the estimates of LMA values.

METHODS

We examined to what extent estimates of LMA based on whole leaves match those based on discs using 334 woody species from a wide range of biomes (tropics, subtropics, savanna, and temperate), whether the relationship varied by leaf morphology (tissue density, leaf area, leaf thickness), punch size (0.6- and 1.0-cm diameter), and whether the extent of intraspecifc variation for each species matches.

RESULTS

Disc-based estimates of species mean LMA matched the whole-leaf estimates well, and whole-leaf LMA tended to be 9.69% higher than leaf-disc LMA. The ratio of whole-leaf LMA to leaf-disc LMA was higher for species with higher leaf tissue density and larger leaves, and variance in the ratio was greater for species with lower leaf tissue density and thinner leaves. Estimates based on small leaf discs also inflated the ratio. The extent of the intraspecific variation only weakly matched between whole-leaf and disc-based estimates (R²  = 0.08).

CONCLUSIONS

Our results suggest that simple conversion between whole-leaf and leaf-disc LMA is difficult for species obtained with a small leaf punch, but it should be possible for species obtained with a large+ leaf punch. Accurately representing leaf traits will likely require careful selection between leaf-disc and whole-leaf traits depending on the objectives. Quantifying intraspecific variation using leaf discs should be also considered with caution.

A cost-benefit analysis of leaf carbon economy with consideration of seasonal changes in leaf traits for sympatric deciduous and evergreen congeners: implications for their coexistence

Deciduous and evergreen species, which have evolved repeatedly across different clades, can coexist in a given environment despite substantial differences in their leaf traits. It remains unclear how these two groups differ in the development of leaf traits over their lifespans or how their carbon economy - the balance between lifetime carbon gain and leaf construction cost - is determined. We determined the photosynthetic rate (A_area ), leaf mass per area (LMA), leaf mechanical strength and leaf water potentials and estimated the lifetime carbon gain and leaf construction cost of five closely related pairs of evergreen and deciduous species co-occurring in a temperate forest. A_area of evergreen species was lower during their first spring, similar in summer and higher than the autumn until the following spring than their deciduous counterparts. Leaf mechanical strength, osmotic pressures and LMA increased continuously towards winter in evergreen species while remaining largely constant in deciduous species. The ratio of lifetime carbon gain to leaf construction cost was similar between the two groups. The additional cost associated with enduring winter is paid back by a longer revenue of photosynthesis in evergreen species, allowing evergreen and deciduous leaf habits to coexist in the seasonal environment.

Multi-trait genetic variation in resource-use strategies and phenotypic plasticity correlates with local climate across the range of a Mediterranean oak (Quercus faginea)

Resource-use strategies are hypothesized to evolve along climatic gradients. However, our understanding of the environmental factors driving divergent evolution of resource-use strategies and the relationship between trait genetic variation and phenotypic plasticity is far from complete. Using the Mediterranean tree Quercus faginea as study system, we tested the hypothesis that a conservative resource-use strategy with increased drought tolerance and reduced phenotypic plasticity has evolved in areas with longer and more severe dry seasons. We conducted a glasshouse experiment in which we measured leaf morphological, physiological, growth and allocation traits in seedlings from 10 range-wide climatically contrasting populations, grown under two different watering treatments. Both univariate and multivariate analyses revealed a genetic gradient of resource-use strategies and phenotypic plasticity associated with provenance climate. In particular, populations from harsher (drier and colder) environments had more sclerophyllous leaves, lower growth rates, better physiological performance under dry conditions and reduced multi-trait phenotypic plasticity compared to populations from more mesic and milder environments. Our results suggest that contrasting precipitation and temperature regimes play an important role in the adaptive intraspecific evolution of multivariate phenotypes and their plasticity, resulting in coordinated morphology, physiology, growth and allometry according to alternative resource-use strategies.

Warming Responses of Leaf Morphology Are Highly Variable among Tropical Tree Species

Leaf morphological traits vary along climate gradients, but it is currently unclear to what extent this results from acclimation rather than adaptation. Knowing so is important for predicting the functioning of long-lived organisms, such as trees, in a rapidly changing climate. We investigated the leaf morphological warming responses of 18 tropical tree species with early (ES) abd late (LS) successional strategies, planted at three sites along an elevation gradient from 2400 m a.s.l. (15.2 °C mean temperature) to 1300 m a.s.l. (20.6 °C mean temperature) in Rwanda. Leaf size expressed as leaf area (LA) and leaf mass per area (LMA) decreased, while leaf width-to-length ratio (W/L) increased with warming, but only for one third to half of the species. While LA decreased in ES species, but mostly not in LS species, changes in LMA and leaf W/L were common in both successional groups. ES species had lower LMA and higher LA and leaf W/L compared to LS species. Values of LMA and LA of juvenile trees in this study were mostly similar to corresponding data on four mature tree species in another elevation-gradient study in Rwanda, indicating that our results are applicable also to mature forest trees. We conclude that leaf morphological responses to warming differ greatly between both successional groups and individual species, with potential consequences for species competitiveness and community composition in a warmer climate.

Species-specific variation of photosynthesis and mesophyll conductance to ozone and drought in three Mediterranean oaks

Mesophyll conductance (g_mCO2 ) is one of the most important components in plant photosynthesis. Tropospheric ozone (O₃ ) and drought impair physiological processes, causing damage to photosynthetic systems. However, the combined effects of O₃ and drought on g_mCO2 are still largely unclear. We investigated leaf gas exchange during mid-summer in three Mediterranean oaks exposed to O₃ (ambient [35.2 nmol mol^-1 as daily mean]; 1.4 × ambient) and water treatments (WW [well-watered] and WD [water-deficit]). We also examined if leaf traits (leaf mass per area [LMA], foliar abscisic acid concentration [ABA]) could influence the diffusion of CO₂ inside a leaf. The combination of O₃ and WD significantly decreased net photosynthetic rate (P_N ) regardless of the species. The reduction of photosynthesis was associated with a decrease in g_mCO2 and stomatal conductance (g_sCO2 ) in evergreen Quercus ilex, while the two deciduous oaks (Q. pubescens, Q. robur) also showed a reduction of the maximum rate of carboxylation (V_cmax ) and maximum electron transport rate (J_max ) with decreased diffusive conductance parameters. The reduction of g_mCO2 was correlated with increased [ABA] in the three oaks, whereas there was a negative correlation between g_mCO2 with LMA in Q. pubescens. Interestingly, two deciduous oaks showed a weak or no significant correlation between g_sCO2 and ABA under high O₃ and WD due to impaired stomatal physiological behaviour, indicating that the reduction of P_N was related to g_mCO2 rather than g_sCO2 . The results suggest that g_mCO2 plays an important role in plant carbon gain under concurrent increases in the severity of drought and O₃ pollution.

Loss of branches due to winter storms could favor deciduousness in oaks

PREMISE

Ecologists have an incomplete understanding of the factors that select for deciduous, evergreen, and marcescent leaf habits. Evergreens have more opportunities for photosynthesis but may experience costs when abiotic conditions are unfavorable such as during ice and windstorms.

METHODS

We documented branch loss for species of oaks (Quercus spp.) in a common garden in California during an unusual windstorm.

RESULTS

Branches of marcescent trees were more likely to break during the storm, and this pattern had a negligible phylogenetic signature. Branches of evergreen and marcescent species were mostly alive before breaking, which likely accrued a fitness cost, while those of deciduous species were mostly already dead. One explanation for the overrepresentation of broken branches from marcescent species is that their petioles are inflexible and have greater wind loading compared to the flexible petioles of evergreen leaves and the leafless condition of deciduous branches.

CONCLUSIONS

These results suggest that branch loss during unusual winter storms may be an important cost of a marcescent leaf habit.

Leaf density and chemical composition explain variation in leaf mass area with spectral composition among 11 widespread forbs in a common garden

Leaf mass per area (LMA) is a key leaf functional trait correlated with plant strategies dictating morphology, physiology, and biochemistry. Although sunlight is generally accepted as a dominant factor driving LMA, the contribution of each spectral region of sunlight in shaping LMA is poorly understood. In the present study, we grew 11 widespread forb species in a common garden and dissected the traits underpinning differences in LMA, such as its morphological components (leaf density [LD] and leaf thickness [LT]), macroelement, and metabolite composition under five spectral-attenuation treatments: (1) transmitting c. 95% of the whole solar spectrum (> 280 nm), (2) attenuating ultraviolet-B radiation (UV-B), (3) attenuating both UV-A and UV-B radiation, (4) attenuating UV radiation and blue light, (5) attenuating UV radiation, blue, and green light. We found that LMA, LD, and chemical traits varied significantly across species depending on spectral treatments. LMA was significantly increased by UV-B radiation and green light, while LD was increased by UV-A but decreased by blue light. LMA positively correlated with LD across treatments but was only weakly related to LT, suggesting that LD was a better determinate of LMA for this specific treatment. Regarding leaf elemental and metabolite composition, carbon, nitrogen, and total phenolics were all positively correlated with LMA, whereas lignin, non-structural carbohydrates, and soluble sugars had negative relationships with LMA. These trends imply a tradeoff between biomass allocation to structural and metabolically functional components. In conclusion, sunlight can spectrally drive LMA mainly through modifying functional and structural support.

Ecologically driven selection of nonstructural carbohydrate storage in oak trees

Leaf habit is a major axis of plant diversity that has consequences for carbon balance since the leaf is the primary site of photosynthesis. Nonstructural carbohydrates (NSCs) produced by photosynthesis can be allocated to storage and serve as a resiliency mechanism to future abiotic and biotic stress. However, how leaf habit affects NSC storage in an evolutionary context has not been shown. Using a comparative physiological framework and an analysis of evolutionary model fitting, we examined if variation in NSC storage is explained by leaf habit. We measured sugar and starch concentrations in 51 oak species (Quercus spp.) growing in a common garden and representing multiple evolutions of three different leaf habits (deciduous, brevideciduous and evergreen). The best fitting evolutionary models indicated that deciduous oak species are evolving towards higher NSC concentrations than their brevideciduous and evergreen relatives. Notably, this was observed for starch (the primary storage molecule) in the stem (a long-term C storage organ). Overall, our work provides insight into the evolutionary drivers of NSC storage and suggests that a deciduous strategy may confer an advantage against stress associated with a changing world. Future work should examine additional clades to further corroborate this idea.

Effects of arbuscular mycorrhizal fungi on the nitrogen distribution in endangered Torreya jackii under nitrogen limitation

Arbuscular mycorrhizal fungi regulated the distribution of nitrogen in the leaves, thereby facilitating the adaptation of the endangered plant Torreya jackii to a low-nitrogen environment. Rhizophagus irregularis was inoculated into sterilized soil to investigate its impact on the distribution ratio of leaf nitrogen in cell wall proteins, cell membrane proteins, water-soluble proteins, and photosynthetic systems which includes the carboxylation system (P_C), energy metabolism (P_B), and light-harvesting system in the endangered species Torreya jackii. The results showed that R. irregularis reduced the specific leaf weight and the distribution ratio of nitrogen in cell wall proteins in the leaves of T. jackii, whereas it enhanced the distribution ratio of nitrogen in cell membrane proteins and water-soluble proteins. R. irregularis enabled more nitrogen uptake for growth by decreasing the distribution of nitrogen to the structural substances. At low-nitrogen levels, inoculation with R. irregularis improved the plant height (18.78 ~ 36.04%), shoot dry weight (50.53 ~ 64.33%), total dry weight (42.86 ~ 52.82%), maximal net photosynthetic rate (P_max) (16.83 ~ 20.11%), photosynthetic nitrogen use efficiency (PNUE) (40.01 ~ 43.14%), P_C (33.56 ~ 38.59%) and P_B (29.08 ~ 34.02%). However, it did not substantially affect the leaf nitrogen content per unit area or the leaf nitrogen content per unit mass. Moreover, P_max exhibited a significant positive correlation with P_C and P_B, and all three parameters showed a significant positive correlation with the PNUE, thereby revealing that R. irregularis increased the photosynthetic capacity and PNUE of T. jackii through boosting P_C and P_B.