Leaf Dry Mass Per Area Research Articles

Leaf traits divergence and correlations of woody plants among the three plant functional types on the eastern Qinghai-Tibetan Plateau, China.

Leaf traits are important indicators of plant life history and may vary according to plant functional type (PFT) and environmental conditions. In this study, we sampled woody plants from three PFTs (e.g., needle-leaved evergreens, NE; broad-leaved evergreens, BE; broad-leaved deciduous, BD) on the eastern Qinghai-Tibetan Plateau, and 110 species were collected across 50 sites. Here, the divergence and correlations of leaf traits in three PFTs and relationships between leaf traits and environment were studied. The results showed significant differences in leaf traits among three PFTs, with NE plants showed higher values than BE plants and BD plants for leaf thickness (LT), leaf dry matter content (LDMC), leaf dry mass per area (LMA), carbon: nitrogen ratio (C/N), and nitrogen content per unit area (Narea), except for nitrogen content per unit mass (Nmass). Although the correlations between leaf traits were similar across three PFTs, NE plants differed from BE plants and BD plants in the relationship between C/N and Narea. Compared with the mean annual precipitation (MAP), the mean annual temperature (MAT) was the main environmental factor that caused the difference in leaf traits among three PFTs. NE plants had a more conservative approach to survival compared to BE plants and BD plants. This study shed light on the regional-scale variation in leaf traits and the relationships among leaf traits, PFT, and environment. These findings have important implications for the development of regional-scale dynamic vegetation models and for understanding how plants respond and adapt to environmental change.

No Consistent Shift in Leaf Dry Mass per Area Across the Cretaceous-Paleogene Boundary.

The Chicxulub bolide impact has been linked to a mass extinction of plants at the Cretaceous—Paleogene boundary (KPB; ∼66 Ma), but how this extinction affected plant ecological strategies remains understudied. Previous work in the Williston Basin, North Dakota, indicates that plants pursuing strategies with a slow return-on-investment of nutrients abruptly vanished after the KPB, consistent with a hypothesis of selection against evergreen species during the globally cold and dark impact winter that followed the bolide impact. To test whether this was a widespread pattern we studied 1,303 fossil leaves from KPB-spanning sediments in the Denver Basin, Colorado. We used the relationship between petiole width and leaf mass to estimate leaf dry mass per area (LMA), a leaf functional trait negatively correlated with rate of return-on-investment. We found no evidence for a shift in this leaf-economic trait across the KPB: LMA remained consistent in both its median and overall distribution from approximately 67 to 65 Ma. However, we did find spatio-temporal patterns in LMA, where fossil localities with low LMA occurred more frequently near the western margin of the basin. These western margin localities are proximal to the Colorado Front Range of the Rocky Mountains, where an orographically driven high precipitation regime is thought to have developed during the early Paleocene. Among these western Denver Basin localities, LMA and estimated mean annual precipitation were inversely correlated, a pattern consistent with observations of both fossil and extant plants. In the Denver Basin, local environmental conditions over time appeared to play a larger role in determining viable leaf-economic strategies than any potential global signal associated with the Chicxulub bolide impact.

Effects of Water Availability on the Relationships Between Hydraulic and Economic Traits in the Quercus wutaishanica Forests.

Water availability is a key environmental factor affecting plant species distribution, and the relationships between hydraulic and economic traits are important for understanding the species’ distribution patterns. However, in the same community type but within different soil water availabilities, the relationships in congeneric species remain ambiguous. In northwest China, Quercus wutaishanica forests in the Qinling Mountains (QM, humid region) and Loess Plateau (LP, drought region) have different species composition owing to contrasting soil water availability, but with common species occurring in two regions. We analyzed eight hydraulic traits [stomatal density (SD), vein density (VD), wood specific gravity (WSGbranch), lower leaf area: sapwood area (Al: As), stomatal length (SL), turgor loss point (ΨTlp), maximum vessel diameter (Vdmax) and height (Height)] and five economic traits [leaf dry matter content (LDMC), leaf tissue density (TD), leaf dry mass per area (LMA), Leaf thickness (LT) and maximum net photosynthetic rate (Pmax)] of congeneric species (including common species and endemic species) in Q. wutaishanica forests of QM and LP. We explored whether the congeneric species have different economic and hydraulic traits across regions. And whether the relationship between hydraulic and economic traits was determined by soil water availability, and whether it was related to species distribution and congeneric endemic species composition of the same community. We found that LP species tended to have higher SD, VD, WSGbranch, Al: As, SL, ΨTlp and Vdmax than QM species. There was a significant trade-off between hydraulic efficiency and safety across congeneric species. Also, the relationships between hydraulic and economic traits were closer in LP than in QM. These results suggested that relationships between hydraulic and economic traits, hydraulic efficiency and safety played the role in constraining species distribution across regions. Interestingly, some relationships between traits changed (from significant correlation to non-correlation) in common species across two regions (from LP to QM), but not in endemic species. The change of these seven pairs of relationships might be a reason for common species’ wide occurrence in the two Q. wutaishanica forests with different soil water availability. In drought or humid conditions, congeneric species developed different types of adaptation mechanisms. The study helps to understand the environmental adaptive strategies of plant species, and the results improve our understanding of the role of both hydraulic and economic traits during community assembly.

The response of mesophyll conductance to ozone-induced oxidative stress is genotype-dependent in poplar

The CO2 diffusion conductance within the leaf mesophyll (gm) is considered a major limiting factor of photosynthesis. However, the effects of the major secondary air pollutant ozone (O3) on gm have been poorly investigated. Eight genotypes of the economically important tree species Populus × canadensis Moench were exposed to 120 ppb O3 for 21 d. gm showed a genotype-dependent response to O3-induced oxidative stress and was a major limiting factor of net assimilation rate (Anet), ahead of stomatal conductance to CO2 (gsc) and of the maximum carboxylation capacity of the Rubisco enzyme (Vcmax) in half of the tested genotypes. Increased leaf dry mass per area (LMA) and decreased chlorophyll content were linked to the observed gm decrease, but this relationship did not entirely explain the different genotypic gm responses. Moreover, the oxidative stress defence metabolites ascorbate and glutathione were not related to O3 tolerance of gm. However, malondialdehyde probably mitigated the observed gm decrease in some genotypes due to its oxidative stress signalling function. The large variation of gm suggests different regulation mechanisms amongst poplar genotypes under oxidative stress.

Coordination of leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought

BackgroundLeaf hydraulic and economics traits are critical for balancing plant water and CO2 exchange, and their relationship has been widely studied. Leaf anatomical traits determine the efficiency of CO2 diffusion within mesophyll structure. However, it remains unclear whether leaf anatomical traits are associated with leaf hydraulic and economics traits acclimation to long-term drought.ResultsTo address this knowledge gap, eight hydraulic traits, including stomatal and venation structures, four economics traits, including leaf dry mass per area (LMA) and the ratio between palisade and spongy mesophyll thickness (PT/ST), and four anatomical traits related to CO2 diffusion were measured in tomato seedlings under the long-term drought conditions. Redundancy analysis indicated that the long-term drought decreased stomatal conductance (gs) mainly due to a synchronized reduction in hydraulic structure such as leaf hydraulic conductance (Kleaf) and major vein width. Simultaneously, stomatal aperture on the adaxial surface and minor vein density (VDminor) also contributed a lot to this reduction. The decreases in mesophyll thickness (Tmes) and chlorophyll surface area exposed to leaf intercellular air spaces (Sc/S) were primarily responsible for the decline of mesophyll conductance (gm) thereby affecting photosynthesis. Drought increased leaf density (LD) thus limited CO2 diffusion. In addition, LMA may not be important in regulating gm in tomato under drought. Principal component analysis revealed that main anatomical traits such as Tmes and Sc/S were positively correlated to Kleaf, VDminor and leaf thickness (LT), while negatively associated with PT/ST.ConclusionsThese findings indicated that leaf anatomy plays an important role in maintaining the balance between water supply and CO2 diffusion responses to drought. There was a strong coordination between leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.

Quantifying Leaf Trait Covariations and Their Relationships with Plant Adaptation Strategies along an Aridity Gradient.

Simple SummaryPlants usually adopt different strategies to adapt to their surrounding environments. Accurately quantifying plant strategies is of great interest in trait-based ecology, in particular to understand the responses of ecological structures and processes. In the last two decades, these strategies have been described qualitatively; however, the use of quantitative methods is still lacking. In this study, we used a plant functional trait approach to discuss plant strategies along an aridity gradient. We found that eight functional traits divided into four dimensions represent four adaptation strategies: energy balance, resource acquisition, resource investment and water use efficiency. We also concluded that climate and soil together with family (vegetation succession) were the main driving forces of trait covariations. Our study provided a new perspective to understand plant functional responses to aridity gradients, which is helpful for ecological management and vegetation restoration programs in arid regions.A trait-based approach is an effective way to quantify plant adaptation strategies in response to changing environments. Single trait variations have been well depicted before; however, multi-trait covariations and their roles in shaping plant adaptation strategies along aridity gradients remain unclear. The purpose of this study was to reveal multi-trait covariation characteristics, their controls and their relevance to plant adaptation strategies. Using eight relevant plant functional traits and multivariate statistical approaches, we found the following: (1) the eight studied traits show evident covariation characteristics and could be grouped into four functional dimensions linked to plant strategies, namely energy balance, resource acquisition, resource investment and water use efficiency; (2) leaf area (LA) together with traits related to the leaf economic spectrum, including leaf nitrogen content per area (Narea), leaf nitrogen per mass (Nmass) and leaf dry mass per area (LMA), covaried along the aridity gradient (represented by the moisture index, MI) and dominated the trait–environmental change axis; (3) together, climate, soil and family can explain 50.4% of trait covariations; thus, vegetation succession along the aridity gradient cannot be neglected in trait covariations. Our findings provide novel perspectives toward a better understanding of plant adaptations to arid conditions and serve as a reference for vegetation restoration and management programs in arid regions.

Southeastern Rear Edge Populations of Quercus suber L. Showed Two Alternative Strategies to Cope with Water Stress

Climate change models predict an increase in aridity, especially in the regions under Mediterranean-type climates such as the Mediterranean Basin. However, there is a lack of ecophysiological studies supporting the selection of the more drought-adapted ecotypes for reforestation programs. In this study, we analyzed the anatomical and functional adaptations of 18-month-old seedlings to drought on 16 Quercus suber L. populations from the southeastern rear edge of the species distribution in northern Tunisia growing in a common garden, in order to identify the most appropriate material to use in reforestations. The results evidenced that populations from more xeric habitats displayed the highest leaf dry mass per area (LMA) and lowest leaf area (LA) values, together with the largest increase in the bulk modulus of elasticity (Δε) in response to drought (i.e., elastic adjustment). On the other hand, some populations with intermediate values of aridity, LMA and LA displayed the sharpest increase in proline concentration (ΔPro), with a concomitant increase in osmotic potential at full turgor (Δπo) (i.e., osmotic adjustment). Therefore, two different strategies seem to drive the within-species variation of the studied Q. suber populations in response to water scarcity: (i) a water saver strategy for improving water stress tolerance through the maximization of the elastic adjustment; and (ii) a water spender strategy for maintaining water absorption and photosynthetic activity under moderate water stress through the maximization of the osmotic adjustment. We concluded that the higher elastic adjustment, together with reduced LA and increased LMA, implied a better performance under drought stress in the populations of Q. suber from more xeric habitats, which can be considered the most drought-adapted ecotypes and, consequently, the most appropriate for reforestation programs under an eventual increase in aridity.

Leaf-economic strategies across the Eocene-Oligocene transition correlate with dry season precipitation and paleoelevation.

The Eocene-Oligocene transition (EOT; 34-33 Ma) was marked by global cooling and increased seasonality and aridity, leading to a shift in North American floras from subtropical forests to deciduous hardwood forests similar to today. This shift is well documented taxonomically and biogeographically, but its ecological nature is less known. Using the relationship between petiole cross-sectional area and leaf mass, we estimated leaf dry mass per area (LMA), a functional trait tied to plant resource investment and expenditure, at 22 western North American sites spanning the EOT to determine how the broad restructuring of vegetation during this time was reflected in leaf economics. There was no overall shift in LMA between pre-EOT and post-EOT floras; instead, changes in LMA across sites were mostly driven by a negative correlation with dry-season precipitation and a positive correlation with paleoelevation. These patterns held for both whole sites and subsets of sites containing taxa with similar biogeographical histories (taxa that persisted in the highlands across the EOT or that migrated to the lowlands) and are consistent with most observations in extant floras. Our data provide a geological context for understanding environmentally paced changes in leaf-economic strategies, particularly linking leaf economic strategies to dry-season precipitation and paleoelevation.

Responses of leaf traits to low temperature in an evergreen oak at its upper limit

AbstractLow temperature is a major driver of the upper distributional limits of subtropical evergreen broadleaved forests in East Asia. The eco‐physiology of evergreen broadleaved trees at the upper limits could respond to both lower winter temperature and lower averaged annual temperature that covary with elevation. To analyze these responses, we assessed the variations in leaf chemical traits of Cyclobalanopsis gracilis with seasonality and along elevation in the ecotone from subtropical to temperate climate, and analyzed the relationships between traits of mature leaves and temperature. The study showed that the mass‐based nonstructural carbohydrate (NSC) content reached the highest level across elevations during winter; however, the winter NSC content did not differ between elevations. For mature leaves, leaf dry mass per area (LMA) tended to be higher approaching the upper limit. The leaf carbon to phosphorus ratio (C/P) showed an increasing trend with decreasing temperature, as did leaf carbon to nitrogen ratio (C/N) to some extent. The mass‐based P content showed a decreasing trend approaching the upper limit, whereas area‐based P content showed no significant variation. Our main results indicate that leaf NSC content is highest at all elevations in winter, and individuals at high elevations have high LMA and high nutrient use efficiency. The results suggest that for C. gracilis, an increasing leaf NSC results in a baseline protection to cope with cold in winter, which, at higher elevations is supplemented with increasing LMA and nutrient use efficiency to cope with associated low‐temperature stress.

Gas exchange characteristics and their influencing factors for halophytic plant communities on west coast of Bohai Sea.

Water–salt stress and nutrient limitation may affect leaf economic spectrum of halophytes and confuse our understanding on plant physiological principles in a changing world. In this study, three halophytic plant communities of Phragmites australis, Suaeda salsa, and Tamarix chinensis, were selected in two sites (sites 1 and 2) on the west coast of Bohai Sea. The net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), leaf vapor pressure deficit (VPDleaf) and their influencing factors were studied to test the possible carbon assimilation strategies of the halophytes. P. australis had higher Pn, Tr, and Gs than S. salsa and T. chinensis in both sites. Similar trends were found for leaf P and photosynthetic N and P efficiency (PNUE and PPUE, respectively) in one or both sites. By contrast, the leaf dry mass per area (LMA) increased in the order of P. australis < S. salsa < T. chinensis in both sites. For identical species in different sites, Pn, leaf P, and PNUE were lower but Tr, VPDleaf, leaf N, leaf N:P, and PPUE were higher in site 1 than in site 2 for one or more halophytes. Although soil physicochemical properties in different sites explained several variations among the halophytes, two-way ANOVA indicated that the species can explain most of the leaf traits compared with the site. LMA also had significant nonlinear relationships with Pn, Tr, Gs, and VPDleaf. PNUE and PPUE showed positive correlation with Pn in both sites, but they decreased in the power-law function with increasing LMA. Overall, the redundancy analysis showed that the gas exchange capacity of the halophytic plant communities was significantly affected by PPUE (60.0% of explanation), PNUE (57.1%), LMA (35.0%), leaf P (22.0%), and soil N (15.8%).

Oviposition by herbivorous insects induces changes in optical and mechanical properties of Prunus avium leaves

This study of animal–plant interaction focused on the impact of oviposition by an insect on the leaves of Prunus avium (cherries). We examined whether the oviposition by Caliroa cerasi affects leaf mechanical and spectral traits in P. avium. Three cultivars of P. avium were studied. Infested leaves had from 1 to 18 eggs and exhibited higher leaf dry mass per area (LMA) than leaves without eggs. Leaf dry weight and LMA were positively correlated with egg number per leaf. Infested leaves tended to have higher number of trichomes. Leaf thickness and material and structural resistance tended to increase in infested leaves. The reflectance across all wavelengths (500–700 nm) in leaves with larger number of eggs was higher compared to leaves without eggs. Photosynthetic performance was reduced and oxidative activity was increased in leaves with eggs. Extrafloral nectaries increased with increasing the number of eggs per leaf and thus play an important role in defense against herbivores by providing nectar rewards that attract their depredators. These responses to oviposition may be beneficial for the plants in terms of resistance to feeding larvae.

Cell wall properties in Oryza sativa influence mesophyll CO2 conductance.

Diffusion of CO2 from the leaf intercellular air space to the site of carboxylation (gm ) is a potential trait for increasing net rates of CO2 assimilation (Anet ), photosynthetic efficiency, and crop productivity. Leaf anatomy plays a key role in this process; however, there are few investigations into how cell wall properties impact gm and Anet . Online carbon isotope discrimination was used to determine gm and Anet in Oryza sativa wild-type (WT) plants and mutants with disruptions in cell wall mixed-linkage glucan (MLG) production (CslF6 knockouts) under high- and low-light growth conditions. Cell wall thickness (Tcw ), surface area of chloroplast exposed to intercellular air spaces (Sc ), leaf dry mass per area (LMA), effective porosity, and other leaf anatomical traits were also analyzed. The gm of CslF6 mutants decreased by 83% relative to the WT, with c.28% of the reduction in gm explained by Sc . Although Anet /LMA and Anet /Chl partially explained differences in Anet between genotypes, the change in cell wall properties influenced the diffusivity and availability of CO2 . The data presented here indicate that the loss of MLG in CslF6 plants had an impact on gm and demonstrate the importance of cell wall effective porosity and liquid path length on gm .

Hyperspectral reflectance as a tool to measure biochemical and physiological traits in wheat.

Improving photosynthesis to raise wheat yield potential has emerged as a major target for wheat physiologists. Photosynthesis-related traits, such as nitrogen per unit leaf area (Narea) and leaf dry mass per area (LMA), require laborious, destructive, laboratory-based methods, while physiological traits underpinning photosynthetic capacity, such as maximum Rubisco activity normalized to 25 °C (Vcmax25) and electron transport rate (J), require time-consuming gas exchange measurements. The aim of this study was to assess whether hyperspectral reflectance (350-2500 nm) can be used to rapidly estimate these traits on intact wheat leaves. Predictive models were constructed using gas exchange and hyperspectral reflectance data from 76 genotypes grown in glasshouses with different nitrogen levels and/or in the field under yield potential conditions. Models were developed using half of the observed data with the remainder used for validation, yielding correlation coefficients (R2 values) of 0.62 for Vcmax25, 0.7 for J, 0.81 for SPAD, 0.89 for LMA, and 0.93 for Narea, with bias <0.7%. The models were tested on elite lines and landraces that had not been used to create the models. The bias varied between -2.3% and -5.5% while relative error of prediction was similar for SPAD but slightly greater for LMA and Narea.

The physiological responses of various pomegranate cultivars to drought stress and recovery in order to screen for drought tolerance

In order to screen pomegranate cultivars for drought tolerance, few rapid, less expensive and reliable methods were used. Two-year-old pomegranate (Punica granatum L.) plants of various commercial cultivars namely ‘Rabab-e-Neyriz’ (‘Rabab’), ‘Shishe-cap-e-Ferdows’ (‘Shishecap’), ‘Malas-e-Saveh’ (‘M-Saveh’), ‘Malas-e-Yazdi’ (‘M-Yazdi’), and ‘Ghojagh-e-Qom’ (‘Ghojagh’) were grown in large containers filled with a mixture of leaf mould, sand, and soil (1:1:1, by volume) in greenhouse. The plants were subjected to 14-day drought stress by withholding irrigation, followed by re-watering for 7 days. Midday stem water potential (Ψstem), leaf relative water content (RWC), membrane stability index (MSI), leaf dry mass per area (LMA), rapid test for drought tolerance (DTI), gas exchange parameters including net photosynthesis (An), leaf scale transpiration (Tr), and stomatal conductance (gs), and intrinsic water use efficiency (IWUE) were determined in well-watered and drought-stressed plants. All cultivars showed an ability to tolerate drought stress, but ‘Ghojagh’ exhibited more tolerance, with a higher RWC and Ψstem and a greater osmotic adjustment. ‘Ghojagh’ also revealed higher cell membrane stability and IWUE and a lower reduction in net CO2 assimilation rate. This study found that ‘M-Yazdi’ was more vulnerable to severe water stress, and displayed the lowest degree of cell membrane stability as compared to the other examined cultivars and showed no recovery for RWC at the end of recovery period.

Convergent elevation trends in canopy chemical traits of tropical forests.

The functional biogeography of tropical forests is expressed in foliar chemicals that are key physiologically based predictors of plant adaptation to changing environmental conditions including climate. However, understanding the degree to which environmental filters sort the canopy chemical characteristics of forest canopies remains a challenge. Here, we report on the elevation and soil-type dependence of forest canopy chemistry among 75 compositionally and environmentally distinct forests in nine regions, with a total of 7819 individual trees representing 3246 species collected, identified and assayed for foliar traits. We assessed whether there are consistent relationships between canopy chemical traits and both elevation and soil type, and evaluated the general role of phylogeny in mediating patterns of canopy traits within and across communities. Chemical trait variation and partitioning suggested a general model based on four interconnected findings. First, geographic variation at the soil-Order level, expressing broad changes in fertility, underpins major shifts in foliar phosphorus (P) and calcium (Ca). Second, elevation-dependent shifts in average community leaf dry mass per area (LMA), chlorophyll, and carbon allocation (including nonstructural carbohydrates) are most strongly correlated with changes in foliar Ca. Third, chemical diversity within communities is driven by differences between species rather than by plasticity within species. Finally, elevation- and soil-dependent changes in N, LMA and leaf carbon allocation are mediated by canopy compositional turnover, whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. Our findings have broad implications for understanding the global ecology of humid tropical forests, and their functional responses to changing climate.

Functional convergence and phylogenetic divergence during secondary succession of subtropical wet forests in Puerto Rico

AbstractQuestionUnderstanding how the relative importance of different community assembly processes changes during secondary succession of diverse systems remains elusive. Functional and phylogenetic approaches that place species along continuous axes of niche differentiation and evolutionary relatedness, however, are deepening our understanding of the mechanisms that drive successional dynamics. We ask whether successional shifts in the functional and phylogenetic composition of post‐agricultural tropical forests provide evidence for niche partitioning or competitive dominance hierarchies as drivers of successional change.LocationSubtropical wet forests, Puerto Rico.MethodsWe combined data on four functional traits [leaf dry mass per area (LMA), wood density (WD), maximum height (Hmax), seed dry mass] and a well‐resolved molecular phylogeny to characterize taxonomic, functional and phylogenetic composition of sapling and adult tree communities along a regionally replicated chronosequence. We used a null model approach to assess how functional and phylogenetic diversity change with forest age.ResultsCorresponding increases of community‐weighted mean LMA, Hmax and seed mass with forest age reflected a shift in dominance of species with acquisitive resource‐use strategies and small seeds towards species with more conservative resource use and larger seeds. A negative relationship between forest age and local diversity of Hmax and seed mass suggested increased importance of competitive hierarchies for light capture and shade‐tolerant regeneration in older forests. In contrast, the colonization of palms in older forest plots led to a positive relationship between forest age and local phylogenetic diversity, suggesting functional convergence of distantly related lineages on traits that confer competitive dominance under low resource conditions.ConclusionsWe linked both functional and phylogenetic dimensions of community diversity with successional trajectories of post‐agricultural tropical forests. Contrasting patterns of these dimensions of diversity shed light on the underlying community assembly processes. We argue that integrating traits and phylogeny with specific hypotheses about physiological and historical mechanisms is essential for advancing our understanding of the drivers of community change during succession.

A quantitative analysis of phenotypic variations of Metrosideros polymorpha within and across populations along environmental gradients on Mauna Loa, Hawaii.

Metrosideros polymorpha, a dominant tree species in the Hawaiian Islands, shows an extreme phenotypic polymorphism both across gradients of climatic/edaphic conditions and within populations, making it a potentially useful model species for evolutionary study. In order to understand how the phenotypic diversity is maintained within populations as well as across populations, we examined the diversities of several leaf and stem functional traits across five elevations and two soil substrates on the volcanic mountain of Mauna Loa, on the island of Hawaii. Leaf dry mass per area (LMA), a key leaf functional trait, was particularly focused on and analyzed in relation to its underlying components-namely, tissue LMA and trichome LMA (LMA = tissue LMA + trichome LMA). Across populations, tissue LMA increased linearly with elevation while trichome LMA showed unimodal patterns with elevation, which were better correlated with temperature and rainfall, respectively. Substantial phenotypic variations were also found within populations. Interestingly, the variations of tissue LMA were often negatively correlated to trichome LMA within populations, which contrasts with the cross-populations pattern, where a strong positive correlation between tissue LMA and trichome LMA was found. This suggests that phenotypic variations within populations were substantially influenced by local ecological processes. Soil depth (an indicator of local water availability) and tree size (an indicator of colonized timing) modestly explained the within-population variations, implying other local environmental factors and/or random processes are also important in local phenotypic diversity. This study provides an insight about how phenotypic diversity of plant species is maintained from local to landscape levels.

Morphological and anatomical determinants of mesophyll conductance in wild relatives of tomato (Solanum sect. Lycopersicon, sect. Lycopersicoides; Solanaceae)

Natural selection on photosynthetic performance is a primary factor determining leaf phenotypes. The complex CO2 diffusion path from substomatal cavities to the chloroplasts - the mesophyll conductance (g(m)) - limits photosynthetic rate in many species and hence shapes variation in leaf morphology and anatomy. Among sclerophyllous and succulent taxa, structural investment in leaves, measured as the leaf dry mass per area (LMA), has been implicated in decreased gm . However, in herbaceous taxa with high g(m), it is less certain how LMA impacts CO2 diffusion and whether it significantly affects photosynthetic performance. We addressed these questions in the context of understanding the ecophysiological significance of leaf trait variation in wild tomatoes, a closely related group of herbaceous perennials. Although g(m) was high in wild tomatoes, variation in g(m) significantly affected photosynthesis. Even in these tender-leaved herbaceous species, greater LMA led to reduced g(m). This relationship between g(m) and LMA is partially mediated by cell packing and leaf thickness, although amphistomy (equal distribution of stomata on both sides of the leaf) mitigates the effect of leaf thickness. Understanding the costs of increased LMA will inform future work on the adaptive significance of leaf trait variation across ecological gradients in wild tomatoes and other systems.

How do leaf veins influence the worldwide leaf economic spectrum? Review and synthesis

Leaf vein traits are implicated in the determination of gas exchange rates and plant performance. These traits are increasingly considered as causal factors affecting the 'leaf economic spectrum' (LES), which includes the light-saturated rate of photosynthesis, dark respiration, foliar nitrogen concentration, leaf dry mass per area (LMA) and leaf longevity. This article reviews the support for two contrasting hypotheses regarding a key vein trait, vein length per unit leaf area (VLA). Recently, Blonder et al. (2011, 2013) proposed that vein traits, including VLA, can be described as the 'origin' of the LES by structurally determining LMA and leaf thickness, and thereby vein traits would predict LES traits according to specific equations. Careful re-examination of leaf anatomy, published datasets, and a newly compiled global database for diverse species did not support the 'vein origin' hypothesis, and moreover showed that the apparent power of those equations to predict LES traits arose from circularity. This review provides a 'flux trait network' hypothesis for the effects of vein traits on the LES and on plant performance, based on a synthesis of the previous literature. According to this hypothesis, VLA, while virtually independent of LMA, strongly influences hydraulic conductance, and thus stomatal conductance and photosynthetic rate. We also review (i) the specific physiological roles of VLA; (ii) the role of leaf major veins in influencing LES traits; and (iii) the role of VLA in determining photosynthetic rate per leaf dry mass and plant relative growth rate. A clear understanding of leaf vein traits provides a new perspective on plant function independently of the LES and can enhance the ability to explain and predict whole plant performance under dynamic conditions, with applications towards breeding improved crop varieties.

长白山林线树种岳桦幼树叶功能型性状随海拔梯度的变化

通过研究沿不同海拔岳桦幼树叶功能型性状,揭示其对环境的响应机制。结果表明:①随海拔升高,岳桦叶面积(LA)逐渐降低,比叶重(LMA)增加,但LMA较高的可塑性指数表明其适应更依赖叶片的薄厚变化;②岳桦叶绿素含量随海拔升高而显著下降,但类胡萝卜素Car和Car/Chl显著升高,Chlb和Car/Chl表现出较高的可塑性指数,更倾向于吸收蓝紫光和保护光合器官;③岳桦叶氮含量(N_area和N_mass)在海拔1800-1900m间最低,在低海拔和高海拔均表现较高,但Chl/N_mass却随海拔升高而显著增加,N_mass 比N_area具有较高的可塑性指数,对光能的吸收更依赖N_mass对Chl的贡献,高海拔主要将更多的氮投资于光合器官的保护(1900m以上),低海拔则更倾向于光合生产(1800m以下);④随海拔升高,MDA增加,但随之抗氧化物质DS、Pro和APX活性增加,负责对活性氧的抵御和清除,但APX活性最大的可塑性指数表明活性氧的清除更依赖于酶促系统,但在海拔1900m以上,APX活性差异不显著,生理抗性逐渐下降,限制岳桦继续向高海拔生长;⑤抗氧化物质可塑性指数最高,叶绿素和叶形态次之,叶氮最低,表明随海拔升高,岳桦林以保护自身的生存为最主要的适应策略机制,然后以增加吸收光能的Chlb及LMA指标为主要生长策略。;This study focuses on the leaf functional traits of <em>Betula ermanii</em> saplings along the altitude gradient of Changbai Mountain, a Natural Nature Reserve of China, and tries to reveal its environmental response mechanism. The main results are as follows: (1)As altitude increased, the leaf area (LA) of <em>B.ermanii</em> dropped significantly, while leaf dry mass per area (LMA) increased. But it also indicated that it more resorted to leaf thickness changing in the procedure of adaption due to a higher LMA plasticity index. (2)The content of Chlorophyll (Chla, Chlb andChla+b) of <em>B.ermanii</em> reduced as altitude climbing up, while carotenoids (Car) and the ratio of Car to Chla+b(Car/Chl) was just the opposite. A higher Chlb and Car/Chl plasticity index of <em>B.ermanii</em> suggested that it tended to assimilate ultraviolet-blue light and protect photosynthetic organs. (3)The content of Leaf nitrogen (N_area and N_mass) of <em>B.ermanii</em> was the least at altitude 1800-1900m, but was higher at the low and high altitude. However Chl/N_mass increased with height ascending. And absorption of light energy more relied on the contribution of nitrogen to Chl for a higher<em> N</em>_mass plasticity value in order to allocate more nitrogen into chemical defense in higher latitude(1900m above), and photosynthesis in lower latitude(1800m below). (4)With altitude increased, when the growth of<em> B.ermanii</em> was limited by the peroxide (such as MDA), antioxidant DS, Pro and APX activity adaptively increased, which was responsible for resisting and clearing reactive oxygen. The highest APX plasticity index of <em>B.ermanii</em> showed it more relied on enzymatic system to accomplish this process, But APX activity had no significant difference above 1900m, which meant that the physiological resistance decreased gradually, and a higher elevation may limit its distribution.(5)With elevation climbed up, <em>B. ermanii</em> took its own survival as the main policy mechanism due to the highest average plasticity index, and then took Chlb and LMA to absorb light energy as the main growth strategy with a higher plasticity index.