Leaf venation: structure, function, development, evolution, ecology and applications in the past, present and future

Plant Trait Networks: Improved Resolution of the Dimensionality of Adaptation

Functional traits are frequently used to evaluate plant adaptation across environments. Yet, traits tend to have multiple functions and interactions, which cannot be accounted for in traditional correlation analyses. Plant trait networks (PTNs) clarify complex relationships among traits, enable the calculation of metrics for the topology of trait coordination and the importance of given traits in PTNs, and how they shift across communities. Recent studies of PTNs provide new insights into some important topics, including trait dimensionality, trait spectra (including the leaf economic spectrum), stoichiometric principles, and the variation of phenotypic integration along gradients of resource availability. PTNs provide improved resolution of the multiple dimensions of plant adaptation across scales and responses to shifting resources, disturbance regimes, and global change.

Miocene Diversification in the Savannahs Precedes Tetraploid Rainforest Radiation in the African Tree Genus Afzelia (Detarioideae, Fabaceae)

The dating of diversification events, including transitions between biomes, is key to elucidate the processes that underlie the assembly and evolution of tropical biodiversity. Afzelia is a widespread genus of tropical trees, threatened by exploitation for its valuable timber, that presents an interesting system to investigate diversification events in Africa. Africa hosts diploid Afzelia species in the savannahs north and south of the Guineo-Congolian rainforest and autotetraploid species confined to the rainforest. Species delimitation and phylogenetic relationships among the diploid and tetraploid species remained unresolved in previous studies using small amounts of DNA sequence data. We used genotyping-by-sequencing in the five widespread Afzelia species in Africa, the savannah species A. africana and A. quanzensis and the rainforest species A. bipindensis, A. pachyloba, and A. bella. Maximum likelihood and coalescent approaches resolved all species as monophyletic and placed the savannah and rainforest taxa into two separate clades corresponding to contrasted ploidy levels. Our data are thus compatible with a single biome shift in Afzelia in Africa, although we were unable to conclude on its direction. SNAPP calibrated species trees show that the savannah diploids started to diversify early, at 12 (9.09-14.89) Ma, which contrasts with a recent and rapid diversification of the rainforest tetraploid clade, starting at 4.22 (3.12 - 5.36) Ma. This finding of older diversification in a tropical savannah clade vs. its sister rainforest clade is exceptional; it stands in opposition to the predominant observation of young ages for savannahs lineages in tropical regions during the relatively recent expansion of the savannah biome.

Differences in leaf physiological and morphological traits between Camellia japonica and Camellia reticulata

Plants of the genus Camellia are widely cultivated throughout the world as ornamentals because of their bright and large flowers. The widely cultivated varieties are mainly derived from the mutant lines and hybrid progenies of Camellia japonica Linn. and Camellia reticulata Lindl. While their geographical distributions and environmental adaptabilities are significantly different, no systematic comparison has been conducted between these two species. To investigate differences in how these plants have adapted to their environments, we measured photosynthesis and 20 leaf functional traits of C. japonica and C. reticulata grown under the same conditions. Compared with C. japonica, C. reticulata showed higher values for light saturation point, light-saturated photosynthetic rate, leaf dry mass per unit area and stomatal area, but lower values for apparent quantum efficiency, leaf size, stomatal density and leaf nitrogen content per unit mass. Stomatal area was positively correlated with light-saturated photosynthetic rate and light saturation point, but negatively correlated with stomatal density. The differences between C. reticulata and C. japonica were mainly reflected in their adaptations to light intensity and leaf morphological traits. C. reticulata is better adapted to high light intensity than C. japonica. This difference is related to the two species' differing life forms. Thus, leaf morphological traits have played an important role in the light adaptation of C. reticulata and C. japonica, and might be first noticed and selected during the breeding process. These findings will contribute to the cultivation of camellia plants.

Leaf size of woody dicots predicts ecosystem primary productivity

A key challenge in ecology is to understand the relationships between organismal traits and ecosystem processes. Here, with a novel dataset of leaf length and width for 10 480 woody dicots in China and 2374 in North America, we show that the variation in community mean leaf size is highly correlated with the variation in climate and ecosystem primary productivity, independent of plant life form. These relationships likely reflect how natural selection modifies leaf size across varying climates in conjunction with how climate influences canopy total leaf area. We find that the leaf size-primary productivity functions based on the Chinese dataset can predict productivity in North America and vice-versa. In addition to advancing understanding of the relationship between a climate-driven trait and ecosystem functioning, our findings suggest that leaf size can also be a promising tool in palaeoecology for scaling from fossil leaves to palaeo-primary productivity of woody ecosystems.

A Fast and Automatic Method for Leaf Vein Network Extraction and Vein Density Measurement Based on Object-Oriented Classification

Rapidly determining leaf vein network patterns and vein densities is biologically important and technically challenging. Current methods, however, are limited to vein contour extraction. Further image processing is difficult, and some leaf vein traits of interest therefore cannot be quantified. In this study, we proposed a novel method for the fast and accurate determination of leaf vein network patterns and vein density. Nine tree species with different leaf characteristics and vein types were applied to verify this method. To overcome the image processing difficulties at the microscopic scale, we adopted the remote object-oriented classification method applied comprehensively in the field of remote sensing research. The key to this approach is to determine the universally applicable leaf vein extraction threshold values (scale parameter, shape parameter, compactness parameter, brightness feature, spectral feature and geometric feature). Based on our analysis, the following recommended threshold values were determined: the scale parameter was 250, the shape parameter was 0.7, the compactness parameter was 0.3, the brightness feature value was 230∼280, the spectral feature value was 180∼230, and the geometric feature value was less than 2. With the optimal extraction parameters applied, the extraction precision was above 96.40% on average for the nine species studied. The leaf vein density calculation rate increased by more than 87.3% compared to that of the traditional methods. The results showed that this method is accurate, fast, flexible and complementary to existing technologies. It is an effective tool for the fast extraction of vein networks and the exploration of leaf vein characteristics, particularly for large-scale studies in plant vein physiology.

Variation within laminae: Semi-automated methods for quantifying leaf venation using phenoVein

PREMISE

Physiological processes may vary within leaf laminae; however, the accompanying heterogeneity in leaf venation is rarely investigated because its quantification can be time consuming. Here we introduce accelerated protocols using existing software to increase sample throughput and ask whether laminae venation varies among three crop types and four subspecies of Brassica rapa.

METHODS

FAA (formaldehyde, glacial acetic acid, and ethanol)-fixed samples were stored in ethanol. Without performing any additional clearing or staining, we tested two methods of image acquisition at three locations along the proximal-distal axis of the laminae and estimated the patterns of venation using the program phenoVein. We developed and made available an R script to handle the phenoVein output and then analyzed our data using linear mixed-effects models.

RESULTS

Beyond fixation and storage, staining and clearing are not necessary to estimate leaf venation using phenoVein if the images are acquired using a stereomicroscope. All estimates of venation required some manual adjustment. We found a significant effect of location within the laminae for all aspects of venation.

DISCUSSION

By removing the clearing and staining steps and utilizing the semi-automated program phenoVein, we quickly and cheaply acquired leaf venation data. Venation may be an important target for crop breeding efforts, particularly if intralaminar variation correlates with variation in physiological processes, which remains an open question.

Functional Divergence Drives Invasibility of Plant Communities at the Edges of a Resource Availability Gradient

Invasive Alien Species (IAS) are a serious threat to biodiversity, severely affecting natural habitats and species assemblages. However, no consistent empirical evidence emerged on which functional traits or trait combination may foster community invasibility. Novel insights on the functional features promoting community invasibility may arise from the use of mechanistic traits, like those associated with drought resistance, which have been seldom included in trait-based studies. Here, we tested for the functional strategies of native and invasive assemblage (i.e., environmental filtering hypothesis vs. niche divergence), and we assessed how the functional space determined by native species could influence community invasibility at the edges of a resource availability gradient. Our results showed that invasive species pools need to have a certain degree of differentiation in order to persist in highly invaded communities, suggesting that functional niche divergence may foster community invasibility. In addition, resident native communities more susceptible to invasion are those which, on average, have higher resource acquisition capacity, and lower drought resistance coupled with an apparently reduced water-use efficiency. We advocate the use of a mechanistic perspective in future research to comprehensively understand invasion dynamics, providing also new insights on the factors underlying community invasibility in different ecosystems.

Optimal Community Assembly Related to Leaf Economic- Hydraulic-Anatomical Traits

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.

Transportation networks inspired by leaf venation algorithms

Biological systems have adapted to environmental constraints and limited resource availability. In the present study, we evaluate the algorithm underlying leaf venation (LV) deployment using graph theory. We compare the traffic balance, travel and cost efficiency of simply-connected LV networks to those of the fan tree and of the spanning tree. We use a Pareto front to show that the total length of leaf venations (LVs) is close to optimal. Then we apply the LV algorithm to design transportation networks in the city of Atlanta. Results show that leaf-inspired models can perform similarly or better than computer-intensive optimization algorithms in terms of network cost and service performance, which could facilitate the design of engineering transportation networks.

Linking vein properties to leaf biomechanics across 58 woody species from a subtropical forest

Leaf venations have elements with relatively lower elasticity than other leaf tissue components, which are thought to contribute to leaf biomechanics. A better mechanistic understanding of relationships between vein traits and leaf mechanical properties is essential for ecologically relevant interpretation of leaf structural variations. We investigated 13 major (first to third order) and minor (>third order) vein traits, six leaf mechanical properties and other structural traits across 58 woody species from a subtropical forest to elucidate how vein traits contribute to leaf biomechanics. Across species, vein dry mass density (ρ_v ), total vein dry mass per leaf area (VMA) and minor vein diameter (VD_min ), but not the lower-order vein density (VLA_1•2 ), were positively correlated with leaf force to punch (F_p ) and force to tear (F_t ). Structural equation models showed that ρ_v and VD_min not only contribute to leaf mechanical properties directly (direct pathway), but also had impacts on leaf biomechanics by influencing leaf thickness and leaf dry mass per area (indirect pathway). Our study demonstrated that vein dry mass density and minor vein diameter are the key vein properties for leaf biomechanics. We also suggest that the mechanical characteristics of venations are potential factors influencing leaf mechanical resistance, structure and leaf economics spectrum.

Improving water use efficiency by changing hydraulic and stomatal characteristics in soybean exposed to drought: the involvement of nitric oxide

A variety of cellular responses is needed to ensure the plants survival during drought, but little is known about the signaling mechanisms involved in this process. Soybean cultivars (EMBRAPA 48 and BR 16, tolerant and sensitive to drought, respectively) were exposed to the following treatments: control conditions (plants in field capacity), drought (20% of available water in the soil), sodium nitroprusside (SNP) treatment (plants irrigated and treated with 100-µM SNP [SNP-nitric oxide (NO) donor molecule], and Drought + SNP (plants subjected to drought and SNP treatment). Plants remained in these conditions until the reproductive stage and were evaluated for physiological (photosynthetic pigments, chlorophyll a fluorescence and gas exchange rates), hydraulic (water potential, osmotic potential and leaf hydraulic conductivity) and morpho-anatomical traits (biomass, venation density and stomatal characterization). Exposure to water deficit considerably reduced water potential in both cultivars and resulted in decrease in photosynthesis and biomass accumulation. The addition of the NO donor attenuated these damaging effects of water deficit and increased the tolerance index of both cultivars. The results showed that NO was able to reduce plant's water loss, while maintaining their biomass production through alteration in stomatal characteristics, hydraulic conductivity and the biomass distribution pattern. These hydraulic and morpho-anatomical alterations allowed the plants to obtain, transport and lose less water to the atmosphere, even in water deficit conditions.

Phenotypic plasticity and genetic adaptation of functional traits influences intra-specific variation in hydraulic efficiency and safety

Understanding which hydraulic traits are under genetic control and/or are phenotypically plastic is essential in understanding how tree species will respond to rapid shifts in climate. We quantified hydraulic traits in Eucalyptus obliqua L'Her. across a precipitation gradient in the field to describe (i) trait variation in relation to long-term climate and (ii) the short-term (seasonal) ability of traits to adjust (i.e., phenotypic plasticity). Seedlings from each field population were raised under controlled conditions to assess (iii) which traits are under strong genetic control. In the field, drier populations had smaller leaves with anatomically thicker xylem vessel walls, a lower leaf hydraulic vulnerability and a lower water potential at turgor loss point, which likely confers higher hydraulic safety. Traits such as the water potential at turgor loss point and ratio of sapwood to leaf area (Huber value) showed significant adjustment from wet to dry conditions in the field, indicating phenotypic plasticity and importantly, the ability to increase hydraulic safety in the short term. In the nursery, seedlings from drier populations had smaller leaves and a lower leaf hydraulic vulnerability, suggesting that key traits associated with hydraulic safety are under strong genetic control. Overall, our study suggests a strong genetic control over traits associated with hydraulic safety, which may compromise the survival of wet-origin populations in drier future climates. However, phenotypic plasticity in physiological and morphological traits may confer sufficient hydraulic safety to facilitate genetic adaptation.

Plant Phylogeny and Growth Form as Drivers of the Altitudinal Variation in Woody Leaf Vein Traits

Variation in leaf veins along environmental gradients reflects an important adaptive strategy of plants to the external habitats, because of their crucial roles in maintaining leaf water status and photosynthetic capacity. However, most studies concentrate on a few species and their vein variation across horizontal spatial scale, we know little about how vein traits shift along the vertical scale, e.g., elevational gradient along a mountain, and how such patterns are shaped by plant types and environmental factors. Here, we aimed to investigate the variation in leaf vein traits (i.e., vein density, VD; vein thickness, VT; and vein volume per unit leaf area, VV) of 93 woody species distributed along an elevational gradient (1,374-3,375 m) in a temperate mountain in China. Our results showed that altitude-related trends differed between growth forms. Tree plants from higher altitudes had lower VD but higher VT and VV than those from lower altitude; however, the opposite tend was observed in VD of shrubs, and no significant altitudinal changes in their VT or VV. Plant phylogenetic information at the clade level rather than climate explained most of variation in three leaf vein traits (17.1-86.6% vs. <0.011-6.3% explained variance), supporting the phylogenetic conservatism hypothesis for leaf vein traits. Moreover, the phylogenetic effects on vein traits differed between trees and shrubs, with the vein traits of trees being relatively more conserved. Together, our study provides new picture of leaf vein variation along the altitude, and highlights the importance of taking plant phylogeny into consideration when discussing trait variation from an ecological to a biogeographic scale.

Genome duplication effects on functional traits and fitness are genetic context and species dependent: studies of synthetic polyploid Fragaria

PREMISE

Divergence in functional traits and adaptive responses to environmental change underlies the ecological advantage of polyploid plants in the wild. While established polyploids may benefit from combined outcomes of genome doubling, hybridization, and polyploidy-enabled adaptive evolution, whether genome doubling alone can drive ecological divergence or whether the outcome is genetically variable remains less clear.

METHODS

Using synthetic, colchicine-induced, autotetraploid (4x) plants derived from self-pollinated diploid (2x) seeds, and their colchicine-treated but unconverted diploid (2x.nc) full sibs from two diploid wild strawberry taxa (Fragaria vesca subsp. vesca and F. vesca subsp. bracteata), we examined the effects of genome doubling on functional traits, heat stress tolerance, and fitness components across taxa and maternal families (i.e., genetic families) within taxa.

RESULTS

Comparisons between 2x and 2x.nc plants indicated a negligible effect of colchicine treatment on functional traits. Genome doubling increased stomatal length and decreased stomatal density, specific leaf area, and leaf vein density, recapitulating patterns observed in wild polyploid Fragaria. Trichome density, heat stress tolerance, and relative growth rate were not significantly affected by genome doubling. Although clonal reproduction was reduced in response to genome doubling, this effect was strongly genetic-family dependent.

CONCLUSIONS

The results suggest that genome doubling during incipient speciation alone can generate ecological divergence and variation among genetic lineages. This response potentially allows for rapid short-term evolutionary adaptation and fuels genomic diversity and independent origins of polyploidy.

Natural genetic variation in photosynthesis: an untapped resource to increase crop yield potential?

Raising crop yield potential is a major goal to ensure food security for the growing global population. Photosynthesis is the primary determinant of crop productivity and any gain in photosynthetic CO2 assimilation per unit of leaf area (A) has the potential to increase yield. Significant intraspecific variation in A is known to exist in various autotrophic organs that represent an unexploited target for crop improvement. However, the large number of factors that influence photosynthetic rates often makes it difficult to measure or estimate A under dynamic field conditions (i.e. fluctuating light intensities or temperatures). This complexity often results in photosynthetic capacity, rather than realized photosynthetic rates being used to assess natural variation in photosynthesis. Here we review the work on natural variation in A, the different factors determining A and their interaction in yield formation. A series of drawbacks and perspectives are presented for the most common analyses generally used to estimate A. The different yield components and their determination based on different photosynthetic organs are discussed with a major focus on potential exploitation of various traits for crop improvement. To conclude, an example of different possibilities to increase yield in wheat through enhancing A is illustrated.

Covariance of Sun and Shade Leaf Traits Along a Tropical Forest Elevation Gradient

Foliar trait adaptation to sun and shade has been extensively studied in the context of photosynthetic performance of plants, focusing on nitrogen allocation, light capture and use via chlorophyll pigments and leaf morphology; however, less is known about the potential sun-shade dichotomy of other functionally important foliar traits. In this study, we measured 19 traits in paired sun and shade leaves along a 3,500-m elevation gradient in southern Peru to test whether the traits differ with canopy position, and to assess if relative differences vary with species composition and/or environmental filters. We found significant sun-shade differences in leaf mass per area (LMA), photosynthetic pigments (Chl ab and Car), and δ¹³C. Sun-shade offsets among these traits remained constant with elevation, soil substrates, and species compositional changes. However, other foliar traits related to structure and chemical defense, and those defining general metabolic processes, did not differ with canopy position. Our results suggest that whole-canopy function is captured in many traits of sun leaves; however, photosynthesis-related traits must be scaled based on canopy light extinction. These findings show that top-of-canopy measurements of foliar chemistry from spectral remote sensing approaches map directly to whole-canopy foliar traits including shaded leaves that cannot be directly observed from above.

Quantitative Estimation of Leaf Heat Transfer Coefficients by Active Thermography at Varying Boundary Layer Conditions

Quantifying heat and mass exchanges processes of plant leaves is crucial for detailed understanding of dynamic plant-environment interactions. The two main components of these processes, convective heat transfer, and transpiration, are inevitably coupled as both processes are restricted by the leaf boundary layer. To measure leaf heat capacity and leaf heat transfer coefficient, we thoroughly tested and applied an active thermography method that uses a transient heat pulse to compute τ, the time constant of leaf cooling after release of the pulse. We validated our approach in the laboratory on intact leaves of spring barley (Hordeum vulgare) and common bean (Phaseolus vulgaris), and measured τ-changes at different boundary layer conditions.By modeling the leaf heat transfer coefficient with dimensionless numbers, we could demonstrate that τ improves our ability to close the energy budget of plant leaves and that modeling of transpiration requires considerations of convection. Applying our approach to thermal images we obtained spatio-temporal maps of τ, providing observations of local differences in thermal responsiveness of leaf surfaces. We propose that active thermography is an informative methodology to measure leaf heat transfer and derive spatial maps of thermal responsiveness of leaves contributing to improve models of leaf heat transfer processes.

Biomimic Vein-Like Transparent Conducting Electrodes with Low Sheet Resistance and Metal Consumption

In this contribution, inspired by the excellent resource management and material transport function of leaf veins, the electrical transport function of metallized leaf veins is mimicked from the material transport function of the vein networks. By electroless copper plating on real leaf vein networks with copper thickness of only several hundred nanometre up to several micrometre, certain leaf veins can be converted to transparent conductive electrodes with an ultralow sheet resistance 100 times lower than that of state-of-the-art indium tin oxide thin films, combined with a broadband optical transmission of above 80% in the UV-VIS-IR range. Additionally, the resource efficiency of the vein-like electrode is characterized by the small amount of material needed to build up the networks and the low copper consumption during metallization. In particular, the high current density transport capability of the electrode of > 6000 A cm^-2 was demonstrated. These superior properties of the vein-like structures inspire the design of high-performance transparent conductive electrodes without using critical materials and may significantly reduce the Ag consumption down to < 10% of the current level for mass production of solar cells and will contribute greatly to the electrode for high power density concentrator solar cells, high power density Li-ion batteries, and supercapacitors.

Leaf Venation and Morphology Help Explain Physiological Variation in Yucca brevifolia and Hesperoyucca whipplei Across Microhabitats in the Mojave Desert, CA

Different microclimates can have significant impact on the physiology of succulents that inhabit arid environments such as the Mojave Desert (California). We investigated variation in leaf physiology, morphology and anatomy of two dominant Mojave Desert monocots, Yucca brevifolia (Joshua tree) and Hesperoyucca whipplei, growing along a soil water availability gradient. Stomatal conductance (g _s) and leaf thickness were recorded in the field at three different sites (north-western slope, south-eastern slope, and alluvial fan) in March of 2019. We sampled leaves from three individuals per site per species and measured in the lab relative water content at the time of g _s measurements, saturated water content, cuticular conductance, leaf morphological traits (leaf area and length, leaf mass per area, % loss of thickness in the field and in dried leaves), and leaf venation. We found species varied in their g _s: while Y. brevifolia showed significantly higher g _s in the alluvial fan than in the slopes, H. whipplei was highest in the south-eastern slope. The differences in g _s did not relate to differences in leaf water content, but rather to variation in number of veins per mm² in H. whipplei and leaf width in Y. brevifolia. Our results indicate that H. whipplei displays a higher water conservation strategy than Y. brevifolia. We discuss these differences and trends with water availability in relation to species' plasticity in morphology and anatomy and the ecological consequences of differences in 3-dimensional venation architecture in these two species.

Polyurethane-based bionic material simulating the Vis-NIR spectrum and thermal infrared properties of vegetation

Poor stability, the toxicity of the used colorants and complex structure are the main problems for the current spectral simulation materials for vegetation. In this paper, a lightweight (0.052 g cm⁻³) and environmentally friendly bionic porous spectrum simulation material (BPSSM) was developed to simulate the Vis-NIR spectra of natural leaves. The porous structure of BPSSM was used to simulate the mesophyll tissue, which endows the BPSSM with a near-infrared plateau. Moreover, the relationship between pore structure (size, open porosity and volume density) and near-infrared plateau in the spectrum was also studied. The chlorophyll of leaves was simulated by vat dyes or organic pigments, and the green apex and red edge characteristics in the visible region were further adjusted by the chlorophyllin sodium copper salt. The water absorption of BPSSM with 100–120% water contents are consistent with the natural leaves spectral curve channel. Finally, the spectral correlation coefficients (r_m) between BPSSM and different natural leaves are up to 0.984, suggesting that the BPSSM is universally applicable for the simulation of different leaves. Interestingly, the average radiant temperature difference between BPSSM and natural leaves is 0.25 °C within 24 hours, indicating it has similar thermal infrared properties to natural leaves. Moreover, the BPSSM can be combined with textiles to obtain a composite fabric, and its breaking strength and photostability were explored.

Simulation of near-infrared and thermal infrared characteristics of leaves.

Leaf vascular architecture in temperate dicotyledons: correlations and link to functional traits

Using 227 dicotyledonous species in temperate region, we found the relationships among densities of different-order veins, creating diversity of leaf vascular architectures. Dicotyledonous angiosperms commonly possess a hierarchical leaf vascular system, wherein veins of different orders have different functions. Minor vein spacing determines leaf hydraulic efficiency, whereas the major veins provide mechanical support. However, there is limited information on the coordination between these vein orders across species, limiting our understanding of how diversity in vein architecture is arrayed. We aimed to examine the (1) relationships between vein densities at two spatial scales (lower- vs. higher-order veins and among minor veins) and (2) relationships of vein densities with plant functional traits. We studied ten traits related to vein densities and three functional traits (leaf dry mass per area [LMA], leaf longevity [LL], and adult plant height [H_adult]) for 227 phylogenetically diverse plant species that occur in temperate regions and examined the vein-vein and vein-functional traits relationships across species. The densities of lower- and higher-order veins were positively correlated across species. The minor vein density was positively correlated with the densities of both areoles and free-ending veins, and vascular networks with higher minor vein density tended to have a lower ratio of free-ending veins to areoles across species. Neither densities of lower- nor higher-order veins were related to LMA and LL. On the other hand, the densities of veins and areoles tended to be positively correlated with H_adult. These results suggest that densities of different-order veins are developmentally coordinated across dicotyledonous angiosperms and form the independent axis in resource use strategies based on the leaf economics spectrum.

Specific responses of sap flux and leaf functional traits to simulated canopy and understory nitrogen additions in a deciduous broadleaf forest

To investigate the effects of atmospheric nitrogen (N) deposition on water use characteristics and leaf traits of trees, we performed canopy (C50) and understory (U50) N additions as NH4NO3 of 50 kg N ha-1 year-1 in a deciduous broadleaf forest of central China. We measured xylem sap flux, crown area:sapwood area ratio (Ca:As), specific leaf area (SLA), mass-based leaf nitrogen content (Nmass) and leaf carbon isotope ratio (δ13C) of Liquidambar formosana Hance, Quercus acutissima Carruth. and Quercus variabilis Blume. Functional traits under different N addition treatments and their responses among tree species were compared and the relationship between xylem sap flux and leaf functional traits under N additions were explored. Results showed that under U50 sap-flux density of xylem significantly decreased for three tree species. But the effect of C50 on sap flux was species-specific. The decrease of sap-flux density with N additions might be caused by the increased Ca/As. δ13C remained constant among different N addition treatments. The responses of SLA and Nmass to N additions were species- and N addition approaches-specific. The correlation of xylem sap flux with leaf traits was not found. Our findings indicate that the effects of canopy N addition on xylem sap flux and leaf functional traits were species-specific and it is necessary to employ canopy N addition for exploring the real responses of forest ecosystems to climate changes in the future researches.

Epidermal patterning and stomatal development in Gnetales

BACKGROUND AND AIMS

The gymnosperm order Gnetales, which has contentious phylogenetic affinities, includes three extant genera (Ephedra, Gnetum, Welwitschia) that are morphologically highly divergent and have contrasting ecological preferences: Gnetum occupies mesic tropical habitats, whereas Ephedra and Welwitschia occur in arid environments. Leaves are highly reduced in Ephedra, petiolate with a broad lamina in Gnetum and persistent and strap-like in Welwitschia. We investigate stomatal development and prepatterning stages in Gnetales, to evaluate the substantial differences among the three genera and compare them with other seed plants.

METHODS

Photosynthetic organs of representative species were examined using light microscopy, scanning electron microscopy and transmission electron microscopy.

KEY RESULTS

Stomata of all three genera possess lateral subsidiary cells (LSCs). LSCs of Ephedra are perigene cells derived from cell files adjacent to the stomatal meristemoids. In contrast, LSCs of Gnetum and Welwitschia are mesogene cells derived from the stomatal meristemoids; each meristemoid undergoes two mitoses to form a 'developmental triad', of which the central cell is the guard mother cell and the lateral pair are LSCs. Epidermal prepatterning in Gnetum undergoes a 'quartet' phase, in contrast with the linear development of Welwitschia. Quartet prepatterning in Gnetum resembles that of some angiosperms but they differ in later development.

CONCLUSIONS

Several factors underpin the profound and heritable differences observed among the three genera of Gnetales. Stomatal development in Ephedra differs significantly from that of Gnetum and Welwitschia, more closely resembling that of other extant gymnosperms. Differences in epidermal prepatterning broadly reflect differences in growth habit between the three genera.

Varieties of the highly dispersible and hypervariable tree, Metrosideros polymorpha, differ in response to mechanical stress and light across a sharp ecotone

PREMISE

The drivers of isolation between sympatric populations of long-lived and highly dispersible conspecific plants are not well understood. In the Hawaiian Islands, the landscape-dominant tree, Metrosideros polymorpha, displays extraordinary phenotypic differences among sympatric varieties despite high dispersibility of its pollen and seeds, thereby presenting a unique opportunity to investigate how disruptive selection alone can maintain incipient forms. Stenophyllous M. polymorpha var. newellii is a recently evolved tree endemic to the waterways of eastern Hawai'i Island that shows striking neutral genetic differentiation from its ancestor, wet-forest M. polymorpha var. glaberrima, despite sympatry of these forms. We looked for evidence for, and drivers of, differential local adaptation of these varieties across the range of M. polymorpha var. newellii.

METHODS

For paired populations of these varieties, we compared seedling performance under contrasting light conditions and a strong water current characteristic of the riparian zone. We also conducted a reciprocal transplant experiment and contrasted adult leaf anatomy.

RESULTS

Results suggest that the riparian zone is harsh and that selection involving the mechanical stress of rushing water, and secondarily, light, led to significant reciprocal immigrant inviability in adjacent forest and riparian environments. The strongest adaptive divergence between varieties was seen in leaves and seedlings from the site with the sharpest ecotone, coincident with the strongest genetic isolation of M. polymorpha var. newellii observed previously.

CONCLUSIONS

These findings suggest that disruptive selection across a sharp ecotone contributes to the maintenance of an incipient riparian ecotype from within a continuous population of a long-lived and highly dispersible tree species.

Potassium mediates coordination of leaf photosynthesis and hydraulic conductance by modifications of leaf anatomy

Typical symptoms of potassium deficiency, characterized as chlorosis or withered necrosis, occur concomitantly with downregulated photosynthesis and impaired leaf water transport. However, the prominent limitations and mechanisms underlying the concerted decreases of leaf photosynthesis and hydraulic conductance are poorly understood. Monocots and dicots were investigated based on responses of photosynthesis and hydraulic conductance and their components and the correlated anatomical determinants to potassium deficiency. We found a conserved pattern in which leaf photosynthesis and hydraulic conductance concurrently decreased under potassium starvation. However, monocots and dicots showed two different hydraulic-redesign strategies: Dicots tended to show a decreased minor vein density, whereas monocots reduced the size of the bundle sheath and its extensions, rather than the minor vein density; both of these strategies may restrain xylem and outside-xylem hydraulic conductance. Additionally, potassium-deprived leaves developed with fewer mesophyll cell-to-cell connections, leading to a reduced area being available for liquid-phase flow. Further quantitative analysis revealed that mesophyll conductance to CO₂ and outside-xylem hydraulic resistance were the major contributors to photosynthetic limitation and increased hydraulic resistance, at more than 50% and 60%, respectively. These results emphasize the importance of potassium in the coordinated regulation of leaf photosynthesis and hydraulic conductance through modifications of leaf anatomy.

Umbrella leaves-Biomechanics of transition zone from lamina to petiole of peltate leaves

In this study we aim to show how the peltate leaves of Colocasia fallax Schott and Tropaeolum majus L., despite their compact design, achieve a rigid connection between petiole and lamina. We have combined various microscopy techniques and computed tomography (CT) scanning for the analysis of the basic structure of the plant's stabilization system. Mechanical tests yielded key mechanical parameters and allowed us to assess the mode of failure. The results of the tests were further processed in a finite element method (FEM) analysis. We were able to show that both plants are able to endure high loads irrespective of the different composition of the supporting structure. C. fallax forms many separate branched strands, whereas T. majus forms fewer strands of greater diameter interconnected in the centre of the transition area, forming a bundle of irregular orientation. This results in different ways to dissipate loads on the lamina. In C. fallax we observed the outer strands of the strengthening tissue under high stress while the inner bundle carries little load. In T. majus the load is distributed more evenly through the juncture in the middle of the transition area. Potential applications include the construction of biomimetical flying roofs.

Effects of major vein blockage and aquaporin inhibition on leaf hydraulics and stomatal conductance

The density and architecture of leaf veins determine the network and efficiency of water transport within laminae and resultant leaf gas exchange and vary widely among plant species. Leaf hydraulic conductance ( Kleaf) can be regulated by vein architecture in conjunction with the water channel protein aquaporin. However, our understanding of how leaf veins and aquaporins affect leaf hydraulics and stomatal conductance ( gs) remains poor. By inducing blockage of the major veins and inhibition of aquaporin activity using HgCl2, we examined the effects of major veins and aquaporins on Kleaf and gs in species with different venation types. A vine species, with thick first-order veins and low vein density, displayed a rapidly declined gs with high leaf water potential in response to vein blockage and a greatly reduced Kleaf and gs in response to aquaporin inhibition, suggesting that leaf aquaporins are involved in isohydric/anisohydric stomatal behaviour. Across species, the decline in Kleaf and gs due to aquaporin inhibition increased linearly with decreasing major vein density, possibly indicating that a trade-off function between vein architecture (apoplastic pathway) and aquaporin activity (cell-to-cell pathway) affects leaf hydraulics.

Automatic hierarchy classification in venation networks using directional morphological filtering for hierarchical structure traits extraction

The extraction of vein traits from venation networks is of great significance to the development of a variety of research fields, such as evolutionary biology. However, traditional studies normally target to the extraction of reticulate structure traits (ReSTs), which is not sufficient enough to distinguish the difference between vein orders. For hierarchical structure traits (HiSTs), only a few tools have made attempts with human assistance, and obviously are not practical for large-scale traits extraction. Thus, there is a necessity to develop the method of automated vein hierarchy classification, raising a new challenge yet to be addressed. We propose a novel vein hierarchy classification method based on directional morphological filtering to automatically classify vein orders. Different from traditional methods, our method classify vein orders from highly dense venation networks for the extraction of traits with ecological significance. To the best of our knowledge, this is the first attempt to automatically classify vein hierarchy. To evaluate the performance of our method, we prepare a soybean transmission image dataset (STID) composed of 1200 soybean leaf images and the vein orders of these leaves are manually coarsely annotated by experts as ground truth. We apply our method to classify vein orders of each leaf in the dataset. Compared with ground truth, the proposed method achieves great performance, while the average deviation on major vein is less than 5 pixels and the average completeness on second-order veins reaches 54.28%.

An integrative bioinspired venation network with ultra-contrasting wettability for large-scale strongly self-driven and efficient water collection

Collection of water from the atmosphere is a potential route to alleviate the global water shortage. However, it is still difficult to find a strategy to collect sufficient water on a large surface and transport it all off the surface without additional energy input. Inspired by redbud leaves, herein, we proposed a new water-collecting configuration. This configuration utilizes an ultra-contrasting wettability venation network with hierarchical micro-nano structures as the skeleton and integrates the strategies evolved by cacti and beetles. This venation network was fabricated by the technology based on ultra-fast lasers. We achieved a near-unity efficiency in collecting and centralizing the condensed water on the entire surface with a large area. Remarkable water collection and centralization capability were obtained. The venation networks manifested the notable enhancements of ∼166%, ∼352% and ∼644% in water collection efficiency when compared with conventional superhydrophobic surfaces at the tilt angles of 90°, 60° and 30°, respectively. This configuration can work continuously at all tilt angles, even against gravity at a negative tilt angle of 90°. In addition, the venation network can maintain excellent water collecting capability even under very arid conditions. The principle and fabrication technology of this venation network make it possible to scale up a practical network device for mass water collection and may be useful for water desalination, heat transfer, microfluidics, lab-on-a-chip, distillation and many other applications.

Leaf structural and hydraulic adjustment with respect to air humidity and canopy position in silver birch (Betula pendula)

Climate change scenarios predict an increase in air temperature and precipitation in northern temperate regions of Europe by the end of the century. Increasing atmospheric humidity inevitably resulting from more frequent rainfall events reduces water flux through vegetation, influencing plants' structure and functioning. We investigated the extent to which artificially elevated air humidity affects the anatomical structure of the vascular system and hydraulic conductance of leaves in Betula pendula. A field experiment was carried out at the Free Air Humidity Manipulation (FAHM) site with a mean increase in relative air humidity (RH) by 7% over the ambient level across the growing period. Leaf hydraulic properties were determined with a high-pressure flow meter; changes in leaf anatomical structure were studied by means of conventional light microscopy and digital image processing techniques. Leaf development under elevated RH reduced leaf-blade hydraulic conductance and petiole conductivity and had a weak effect on leaf vascular traits (vessel diameters decreased), but had no significant influence on stomatal traits or tissue proportions in laminae. Both hydraulic traits and relevant anatomical characteristics demonstrated pronounced trends with respect to leaf location in the canopy-they increased from crown base to top. Stomatal traits were positively correlated with several petiole and leaf midrib vascular traits. The reduction in leaf hydraulic conductance in response to increasing air humidity is primarily attributable to reduced vessel size, while higher hydraulic efficiency of upper-crown foliage is associated with vertical trends in the size of vascular bundles, vessel number and vein density. Although we observed co-ordinated adjustment of vascular and hydraulic traits, the reduced leaf hydraulic efficiency could lead to an imbalance between hydraulic supply and transpiration demand under the extreme environmental conditions likely to become more frequent in light of global climate change.

Two sides to every leaf: water and CO2 transport in hypostomatous and amphistomatous leaves

Leaves with stomata on both upper and lower surfaces, termed amphistomatous, are relatively rare compared with hypostomatous leaves with stomata only on the lower surface. Amphistomaty occurs predominantly in fast-growing herbaceous annuals and in slow-growing perennial shrubs and trees. In this paper, we present the current understanding and hypotheses on the costs and benefits of amphistomaty related to water and CO₂ transport in contrasting leaf morphologies. First, there is no evidence that amphistomatous species achieve higher stomatal densities on a projected leaf area basis than hypostomatous species, but two-sided gas exchange is less limited by boundary layer effects. Second, amphistomaty may provide a specific advantage in thick leaves by shortening the pathway for CO₂ transport between the atmosphere and the chloroplasts. In thin leaves of fast-growing herbaceous annuals, in which both the adaxial and abaxial pathways are already short, amphistomaty enhances leaf-atmosphere gas-exchange capacity. Third, amphistomaty may help to optimise the leaf-interior water status for CO₂ transport by reducing temperature gradients and so preventing the condensation of water that could limit CO₂ diffusion. Fourth, a potential cost of amphistomaty is the need for additional investments in leaf water transport tissue to balance the water loss through the adaxial surface.

Modelling water fluxes in plants: from tissues to biosphere

Contents Summary 1207 I. Introduction 1207 II. A brief history of modelling plant water fluxes 1208 III. Main components of plant water transport models 1208 IV. Stand-scale water fluxes and coupling to climate and soil 1213 V. Water fluxes in terrestrial biosphere models and feedbacks to community dynamics 1215 VI. Outstanding challenges in modelling water fluxes in the soil-plant-atmosphere continuum 1217 Acknowledgements 1218 References 1218 SUMMARY: Models of plant water fluxes have evolved from studies focussed on understanding the detailed structure and functioning of specific components of the soil-plant-atmosphere (SPA) continuum to architectures often incorporated inside eco-hydrological and terrestrial biosphere (TB) model schemes. We review here the historical evolution of this field, examine the basic structure of a simplified individual-based model of plant water transport, highlight selected applications for specific ecological problems and conclude by examining outstanding issues requiring further improvements in modelling vegetation water fluxes. We particularly emphasise issues related to the scaling from tissue-level traits to individual-based predictions of water transport, the representation of nonlinear and hysteretic behaviour in soil-xylem hydraulics and the need to incorporate knowledge of hydraulics within broader frameworks of plant ecological strategies and their consequences for predicting community demography and dynamics.

Hydraulic and Photosynthetic Traits Vary with Successional Status of Woody Plants on the Loess Plateau

Research highlights: Water transport and CO2 diffusion are two important processes that determine the CO2 assimilation efficiency in leaves. The integration of leaf economic and hydraulic traits will help to present a more comprehensive view of the succession of woody plants in arid regions. However, studies on hydraulic traits of plants from different successional stages are still rare compared to that on economic traits in arid regions. Materials and methods: We selected 31 species from shrub stage, pioneer tree stage and late successional stage on the Loess Plateau, and measured five economic traits and five hydraulic traits of these species. Results: We found species from the pioneer tree stage exhibited "fast-growing" characteristics with high maximum net photosynthesis rate (Pmax) and vein density (VD). Species from the late successional stage exhibited "slow-growing" characteristics with low Pmax and VD. Economic traits showed no significant differences among the three stages except for Pmax. Hydraulic traits, such as VD, leaf area to sapwood area ratio and vessel frequency, exhibited significant differences among different stages. Conclusions: Hydraulics may play an important role in the succession of woody plants in arid regions. Hydraulic traits and Pmax, should be combined to investigate succession of woody plants in future studies. The "fast-growing" characteristics of pioneer trees and "slow-growing" characteristics of late successional trees may induce the succession of woody plants.

Life history is a key factor explaining functional trait diversity among subtropical grasses, and its influence differs between C3 and C4 species

Life history and photosynthetic type both affect the economics of leaf physiological function. Annual plants have lower tissue densities and resource-use efficiencies than perennials, while C4 photosynthesis, facilitated in grasses by specific changes in leaf anatomy, improves photosynthetic efficiency and water-use efficiency, especially in hot climates. This study aimed to determine whether C4 photosynthesis affects differences in functional traits between annual and perennial species. We measured 26 traits and characterised niche descriptors for 42 grasses from subtropical China. Differences in the majority of traits were explained by life history. The ranges of annual species (particularly C4 annuals) extended to regions with greater temperature seasonality and lower precipitation, and annuals had less-negative turgor-loss points, higher specific leaf areas, and lower water-use efficiencies, stomatal conductances, and leaf areas per stem area than perennials. Photosynthetic type largely affected leaf physiology as expected, but interacted with life history in determining specific traits. Leaf hydraulic conductance was intermediate in perennials, highest in C4-annuals, and lowest in C3-annuals. Densities of stomata and stem vessels were similar across C3-perennials and C4 species, but stomatal densities were lower and stem vessel densities higher in C3-annuals. Phylogenetic principal component analysis confirmed that in this subtropical environment life history is the predominant axis separating species, and annuals and perennials were more different within C3 than C4 grasses. The interplay between life history and photosynthetic type may be an overlooked factor in shaping the physiological ecology of grasses.

Evolutionary potential varies across populations and traits in the neotropical oak Quercus oleoides

Heritable variation in polygenic (quantitative) traits is critical for adaptive evolution and is especially important in this era of rapid climate change. In this study, we examined the levels of quantitative genetic variation of populations of the tropical tree Quercus oleoides Cham. and Schlect. for a suite of traits related to resource use and drought resistance. We tested whether quantitative genetic variation differed across traits, populations and watering treatments. We also tested potential evolutionary factors that might have shaped such a pattern: selection by climate and genetic drift. We measured 15 functional traits on 1322 1-year-old seedlings of 84 maternal half-sib families originating from five populations growing under two watering treatments in a greenhouse. We estimated the additive genetic variance, coefficient of additive genetic variation and narrow-sense heritability for each combination of traits, populations and treatments. In addition, we genotyped a total of 119 individuals (with at least 20 individuals per population) using nuclear microsatellites to estimate genetic diversity and population genetic structure. Our results showed that gas exchange traits and growth exhibited strikingly high quantitative genetic variation compared with traits related to leaf morphology, anatomy and photochemistry. Quantitative genetic variation differed between populations even at geographical scales as small as a few kilometers. Climate was associated with quantitative genetic variation, but only weakly. Genetic structure and diversity in neutral markers did not relate to coefficient of additive genetic variation. Our study demonstrates that quantitative genetic variation is not homogeneous across traits and populations of Q. oleoides. More importantly, our findings suggest that predictions about potential responses of species to climate change need to consider population-specific evolutionary characteristics.

Functional trait divergence and trait plasticity confer polyploid advantage in heterogeneous environments

Polyploidy, or whole-genome duplication often with hybridization, is common in eukaryotes and is thought to drive ecological and evolutionary success, especially in plants. The mechanisms of polyploid success in ecologically relevant contexts, however, remain largely unknown. We conducted an extensive test of functional trait divergence and plasticity in conferring polyploid fitness advantage in heterogeneous environments, by growing clonal replicates of a worldwide genotype collection of six allopolyploid and five diploid wild strawberry (Fragaria) taxa in three climatically different common gardens. Among leaf functional traits, we detected divergence in trait means but not plasticities between polyploids and diploids, suggesting that increased genomic redundancy in polyploids does not necessarily translate into greater trait plasticity in response to environmental change. Across the heterogeneous garden environments, however, polyploids exhibited fitness advantage, which was conferred by both trait means and adaptive trait plasticities, supporting a 'jack-and-master' hypothesis for polyploids. Our findings elucidate essential ecological mechanisms underlying polyploid adaptation to heterogeneous environments, and provide an important insight into the prevalence and persistence of polyploid plants.

A research agenda for seed-trait functional ecology

Trait-based approaches have improved our understanding of plant evolution, community assembly and ecosystem functioning. A major challenge for the upcoming decades is to understand the functions and evolution of early life-history traits, across levels of organization and ecological strategies. Although a variety of seed traits are critical for dispersal, persistence, germination timing and seedling establishment, only seed mass has been considered systematically. Here we suggest broadening the range of morphological, physiological and biochemical seed traits to add new understanding on plant niches, population dynamics and community assembly. The diversity of seed traits and functions provides an important challenge that will require international collaboration in three areas of research. First, we present a conceptual framework for a seed ecological spectrum that builds upon current understanding of plant niches. We then lay the foundation for a seed-trait functional network, the establishment of which will underpin and facilitate trait-based inferences. Finally, we anticipate novel insights and challenges associated with incorporating diverse seed traits into predictive evolutionary ecology, community ecology and applied ecology. If the community invests in standardized seed-trait collection and the implementation of rigorous databases, major strides can be made at this exciting frontier of functional ecology.

Increasing atmospheric CO2 and canopy temperature induces anatomical and physiological changes in leaves of the C4 forage species Panicum maximum

Changes in leaf anatomy and ultrastructure are associated with physiological performance in the context of plant adaptations to climate change. In this study, we investigated the isolated and combined effects of elevated atmospheric CO₂ concentration ([CO₂]) up to 600 μmol mol^-1 (eC) and elevated temperature (eT) to 2°C more than the ambient canopy temperature on the ultrastructure, leaf anatomy, and physiology of Panicum maximum Jacq. grown under field conditions using combined free-air carbon dioxide enrichment (FACE) and temperature free-air controlled enhancement (T-FACE) systems. Plants grown under eC showed reduced stomatal density, stomatal index, stomatal conductance (g_s), and leaf transpiration rate (E), increased soil-water content (SWC) conservation and adaxial epidermis thickness were also observed. The net photosynthesis rate (A) and intrinsic water-use efficiency (iWUE) were enhanced by 25% and 71%, respectively, with a concomitant increase in the size of starch grains in bundle sheath cells. Under air warming, we observed an increase in the thickness of the adaxial cuticle and a decrease in the leaf thickness, size of vascular bundles and bulliform cells, and starch content. Under eCeT, air warming offset the eC effects on SWC and E, and no interactions between [CO₂] and temperature for leaf anatomy were observed. Elevated [CO₂] exerted more effects on external characteristics, such as the epidermis anatomy and leaf gas exchange, while air warming affected mainly the leaf structure. We conclude that differential anatomical and physiological adjustments contributed to the acclimation of P. maximum growing under elevated [CO₂] and air warming, improving the leaf biomass production under these conditions.

Limits of multifunctionality in tunable networks

Nature is rife with networks that are functionally optimized to propagate inputs to perform specific tasks. Whether via genetic evolution or dynamic adaptation, many networks create functionality by locally tuning interactions between nodes. Here we explore this behavior in two contexts: strain propagation in mechanical networks and pressure redistribution in flow networks. By adding and removing links, we are able to optimize both types of networks to perform specific functions. We define a single function as a tuned response of a single "target" link when another, predetermined part of the network is activated. Using network structures generated via such optimization, we investigate how many simultaneous functions such networks can be programed to fulfill. We find that both flow and mechanical networks display qualitatively similar phase transitions in the number of targets that can be tuned, along with the same robust finite-size scaling behavior. We discuss how these properties can be understood in the context of constraint-satisfaction problems.

Quantification of Leaf Phloem Anatomical Features with Microscopy

Measurements of vein density and foliar minor vein phloem cell numbers, minor vein phloem cell sizes, and transfer cell wall ingrowths provide quantitative proxies for the leaf's capacities to load and export photosynthates. While overall infrastructural capacity for sugar loading and sugar export correlated positively and closely with photosynthetic capacity, the specific targets of the adjustment of minor vein organization varied with phloem-loading mechanism, plant life-cycle characteristics, and environmental growth conditions. Among apoplastic loaders, for which sugar loading into the phloem depends on cell membrane-spanning transport proteins, variation in minor vein density, phloem cell number, and level of cell wall ingrowth (when present) were consistently associated with photosynthetic capacity. Among active symplastic loaders, for which sugar loading into the phloem depends on cytosolic enzymes, variation in vein density and phloem cell size were consistently associated with photosynthetic capacity. All of these anatomical features were also subject to acclimatory adjustment depending on species and environmental conditions, with increased levels of these features supporting higher rates of photosynthesis. We present a procedure for the preparation of leaf tissue for minor vein analysis, using both light and transmission electron microscopy, that facilitates quantification of not only phloem features but also xylem features that provide proxies for foliar water import capacity.

Extended differentiation of veins and stomata is essential for the expansion of large leaves in Rheum rhabarbarum

PREMISE OF THE STUDY

The densities of veins and stomata govern leaf water supply and gas exchange. They are coordinated to avoid overproduction of either veins or stomata. In many species, where leaf area is greater at low light, this coordination is primarily achieved through differential cell expansion, resulting in lower stomatal and vein density in larger leaves. This mechanism would, however, create highly inefficient leaves in species in which leaf area is greater at high light. Here we investigate the role of cell expansion and differentiation as regulators of vein and stomatal density in Rheum rhabarbarum, which produces large leaves under high light.

METHODS

Rheum rhabarbarum plants were grown under full sunlight and 7% of full sunlight. Leaf area, stomatal density, and vein density were measured from leaves harvested at different intervals.

KEY RESULTS

Leaves of R. rhabarbarum expanded at high light were six times larger than leaves expanded at low light, yet vein and stomatal densities were similar. In high light-expanded leaves, minor veins were continuously initiated as the leaves expanded, while an extended period of stomatal initiation, compared to leaves expanded at low light, occurred early in leaf development.

CONCLUSIONS

We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism.

Near-infrared fluorescence imaging for vascular visualization and fungal detection in plants

We found that heptamethine dye IR-820 showed distinct emission peaks in both the NIR-Ia and NIR-Ib windows. IR-820 yielded images of vascular structures in the NIR-Ib window with unprecedented details. NIR-Ib fluorescence imaging was useful not only for studying plant transpiration, but also for detecting and differentiating fungal pathogens.

Optimal Noise-Canceling Networks

Natural and artificial networks, from the cerebral cortex to large-scale power grids, face the challenge of converting noisy inputs into robust signals. The input fluctuations often exhibit complex yet statistically reproducible correlations that reflect underlying internal or environmental processes such as synaptic noise or atmospheric turbulence. This raises the practically and biophysically relevant question of whether and how noise filtering can be hard wired directly into a network's architecture. By considering generic phase oscillator arrays under cost constraints, we explore here analytically and numerically the design, efficiency, and topology of noise-canceling networks. Specifically, we find that when the input fluctuations become more correlated in space or time, optimal network architectures become sparser and more hierarchically organized, resembling the vasculature in plants or animals. More broadly, our results provide concrete guiding principles for designing more robust and efficient power grids and sensor networks.

The arrangement of lateral veins along the midvein of leaves is not related to leaf phyllotaxis

Positions of leaves along a stem usually adhere to a genetically determined, species-specific pattern known as a leaf phyllotaxis. We investigated whether the arrangement of lateral secondary veins along primary midveins adhered to a species-specific pattern that resembled an alternate or opposite phyllotaxis. We analyzed the venation of temperate dicotyledonous species from different taxonomic groups and chose 18 woody and 12 herbaceous species that have reticulated leaf venation. The arrangement of the lateral veins was neither alternate nor opposite for any of the species. Lateral vein arrangements were instead mixtures of symmetric and asymmetric patterns. Our results show that lateral vein arrangements are related neither to stem-level leaf phyllotaxis (alternate vs. opposite) nor to life form (woody vs. herbaceous). Our results are therefore generally consistent with the canalization hypothesis that the locations of lateral veins are not completely specified genetically prior to leaf formation.

Early Miocene CO2 estimates from a Neotropical fossil leaf assemblage exceed 400 ppm

PREMISE OF THE STUDY

The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO₂ records for this interval suggest paradoxically low concentrations (<450 ppm) that are difficult to reconcile with a warmer-than-present global climate.

METHODS

In this study, we use a leaf gas-exchange model to estimate CO₂ concentrations using stomatal characteristics of fossil leaves from a late early Miocene Neotropical assemblage from Panama that we date to 18.01 ± 0.17 Ma via ²³⁸ U/²⁰⁶ Pb zircon geochronology. We first validated the model for Neotropical environments by estimating CO₂ from canopy leaves of 21 extant species in a natural Panamanian forest and from leaves of seven Neotropical species in greenhouse experiments at 400 and 700 ppm.

KEY RESULTS

The results showed that the most probable combined CO₂ estimate from the natural forests and 400 ppm experiments is 475 ppm, and for the 700 ppm experiments is 665 ppm. CO₂ estimates from the five fossil species exhibit bimodality, with two species most consistent with a low mode (528 ppm) and three with a high mode (912 ppm).

CONCLUSIONS

Despite uncertainties, it is very likely (at >95% confidence) that CO₂ during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO₂ concentration at this time, more in keeping with a CO₂ -forced greenhouse climate.