中国东部南北样带暖温带区栎属树种叶片形态性状对气候条件的响应

植物叶片的形态性状能够有效地反映生存环境的变化, 并且影响植物的基本行为和功能。该研究通过获取植物标本提供的叶片形态信息, 结合相关分析和标准化主轴分析, 探讨了南北样带暖温带区栎属(Quercus)树种叶片形态性状对气候条件的响应及适应策略。结果表明: 在南北样带暖温带区, 随着气候条件的变化, 栎属树种的叶片形态性状发生显著的变化。随着年平均气温的降低和年日照时数的增加, 栎属树种叶面积增加, 以利于吸收更多的光照辐射, 并增加叶片的边界层阻力, 减少叶片热量的散失; 而叶片分裂程度的增加不仅可以降低热量的散失, 也可以提高叶片液流的波动以增强叶片的生理活动; 叶脉密度随温度的升高、光照强度和降水量的增加而增加, 以响应叶片蒸腾作用的增强, 提高水分的运输能力和叶片的支撑能力。此外, 为适应南北样带暖温带区气候条件的变化, 栎属树种的叶片形成了一系列的形态性状组合, 随着叶面积的增加, 叶柄长度和叶片分裂程度逐渐增加, 而叶脉密度降低; 随着叶片倾向于向长条状发展, 叶柄长度和叶脉密度也随之增加。     

Estimation of temperature and precipitation from morphological characters of dicotyledonous leaves

The utility of regression and correspondence models for deducing climate from leaf physiognomy was evaluated by the comparative application of different predictive models to the same three leaf assemblages. Mean annual temperature (MAT), mean annual precipitation (MAP), and growing season precipitation (GSP) were estimated from the morphological characteristics of samples of living leaves from two extant forests and an assemblage of fossil leaves. The extant forests are located near Gainesville, Florida, and in the Florida Keys; the fossils were collected from the Eocene Clarno Nut Beds, Oregon. Simple linear regression (SLR), multiple linear regression (MLR), and canonical correspondence analysis (CCA) were used to estimate temperature and precipitation. The SLR models used only the percentage of species having entire leaf margins as a predictor for MAT and leaf size as a predictor for MAP. The MLR models used from two to six leaf characters as predictors, and the CCA used 31 characters. In comparisons between actual and predicted values for the extant forests, errors in prediction of MAT were 0.6°-5.7°C, and errors in prediction of precipitation were 6-89 cm (=6-66%). At the Gainesville site, seven models underestimated MAT and only one overestimated it, whereas at the Keys site, all eight models overestimated MAT. Precipitation was overestimated by all four models at Gainesville, and by three of them at the Keys. The MAT estimates from the Clarno leaf assemblage ranged from 14.3° to 18.8°C, and the precipitation estimates from 227 to 363 cm for MAP and from 195 to 295 cm for GSP.     

区域尺度上栓皮栎叶性状变异及其与气候因子的关系

叶片在长期进化过程中对环境变化敏感且对气候变化的响应表现出表型可塑性。栓皮栎(Quercus varaibilis)是亚洲大陆地理分布最广泛的树种之一,横跨温带和亚热带地区。本文在中国中东部区域内,选取了25个天然栓皮栎林种群,测量了其叶柄长度、叶片长度、叶片宽度、叶片面积、叶片干重等,并计算了比叶面积和叶形指数(叶片长宽比)等叶性状特征,探讨了区域尺度上叶片性状变异与气候因子关系的格局。结果表明,栓皮栎叶片性状在种群间和种群内均存在显著的变异;叶片宽度与年均温度呈显著的负相关,叶片宽度和叶片面积与纬度均呈显著正相关,说明叶宽及叶片面积相对于其他指标对气候因子的影响变化更敏感,并且在这一区域尺度上温度影响着叶片大小的变异格局。本研究结果为在全球气候变化背景下了解区域尺度上栓皮栎对环境变化的适应与响应机制提供了基础。     

Paleotemperature proxies from leaf fossils reinterpreted in light of evolutionary history

Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of untoothed-leaf species (NT). This uniformitarian approach should provide accurate paleoclimate reconstructions under the core assumption that leaf-trait variation principally results from adaptive environmental convergence, and because variation is thus largely independent of phylogeny it should be constant through geologic time. Although much research acknowledges and investigates possible pitfalls in paleoclimate estimation based on leaf physiognomy, the core assumption has never been explicitly tested in a phylogenetic comparative framework. Combining an extant dataset of 21 leaf traits and temperature with a phylogenetic hypothesis for 569 species-site pairs at 17 sites, we found varying amounts of non-random phylogenetic signal in all traits. Phylogenetic vs. standard regressions generally support prevailing ideas that leaf-traits are adaptively responding to temperature, but wider confidence intervals, and shifts in slope and intercept, indicate an overall reduced ability to predict climate precisely due to the non-random phylogenetic signal. Notably, the modern-day relation of proportion of untoothed taxa with mean annual temperature (NT-MAT), central in paleotemperature inference, was greatly modified and reduced, indicating that the modern correlation primarily results from biogeographic history. Importantly, some tooth traits, such as number of teeth, had similar or steeper slopes after taking phylogeny into account, suggesting that leaf teeth display a pattern of exaptive evolution in higher latitudes. This study shows that the assumption of convergence required for precise, quantitative temperature estimates using present-day leaf traits is not supported by empirical evidence, and thus we have very low confidence in previously published, numerical paleotemperature estimates. However, interpreting qualitative changes in paleotemperature remains warranted, given certain conditions such as stratigraphically closely-spaced samples with floristic continuity.     

Leaf age and season influence the relationships between leaf nitrogen, leaf mass per area and photosynthesis in maple and oak trees

Abstract. Seasonal changes in photosynthesis, leaf nitrogen (N) contents and leaf mass per area (LMA) were observed over three growing seasons in open-grown sun-lit leaves of red maple ( Acer rubrum ), sugar maple ( A. sacchamm ) and northern pin oak ( Quereus ellipsoidalis ) trees in southern Wisconsin. Net photosynthesis and leaf N were highly linearly correlated on both mass and area bases within all species from late spring until leaf senescence in fall. Very early in the growing season leaves had high N concentrations, but low photosynthetic rates per unit leaf N, suggesting that leaves were not fully functionally developed at that time. Leaf N per unit area and LMA had nonparallel seasonal patterns, resulting in differing relationships between leaf N/area and LMA in the "early versus late growing season. As a result of differences in seasonal patterns between leaf N/area and LMA, net photosynthesis/area was higher for a given LMA in the spring than fall, and the overall relationships between these two parameters were poor.     

Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications

? Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. ? Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. ? We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. ? Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.     

The scaling of leaf area and mass: the cost of light interception increases with leaf size

For leaves, the light-capturing surface area per unit dry mass investment (specific leaf area, SLA) is a key trait from physiological, ecological and biophysical perspectives. To address whether SLA declines with leaf size, as hypothesized due to increasing costs of support in larger leaves, we compiled data on intraspecific variation in leaf dry mass (LM) and leaf surface area (LA) for 6334 leaves of 157 species. We used the power function LM=alpha LAbeta to test whether, within each species, large leaves deploy less surface area per unit dry mass than small leaves. Comparing scaling exponents (beta) showed that more species had a statistically significant decrease in SLA as leaf size increased (61) than the opposite (7) and the average beta was significantly greater than 1 (betamean=1.10, 95% CI 1.08-1.13). However, scaling exponents varied markedly from the few species that decreased to the many that increased SLA disproportionately fast as leaf size increased. This variation was unrelated to growth form, ecosystem of origin or climate. The average within-species tendency found here (allometric decrease of SLA with leaf size, averaging 13%) is in accord with concurrent findings on global-scale trends among species, although the substantial scatter around the central tendency suggests that the leaf size dependency does not obligately shape SLA. Nonetheless, the generally greater mass per unit leaf area of larger than smaller leaves directly translates into a greater cost to build and maintain a unit of leaf area, which, all else being equal, should constrain the maximum leaf size displayed.     

Oviposition site preference and larval mortality in a leaf-mining moth

Abstract. 1. The univoltine leaf-mining moth, Lithocolletis quercus Ams., is endemic to Israel, where it spends its 10.5 month larval period feeding only in the leaves of Quercus calliprinos Webb.
2. We compared patterns of egg deposition and sources of larval mortality to test whether oviposition patterns and site preferences confer an enhanced likelihood of larval survival.
3. Dominant sources of larval mortality were premature leaf abscission and death from unknown causes, whereas predation, parasitism and intraspecific interference accounted for relatively little larval mortality.
4. Eggs, and thus mines, were aggregated among leaves of host trees even though premature leaf abscission was positively correlated with density of mines per leaf. Interference competition among larvae was the only other density-dependent mortality factor.
5. Oviposition patterns within leaves mitigated the probability of death from larval interference, and probably also from early leaf abscission.
6. Despite these density-dependent mortality factors, overall probability of larval survival to pupation was independent of initial density of mines on a leaf.
7. The long larval period allows synchrony between oviposition flights and times of predictable resource availability.     

青藏高原东缘主要针叶树种叶片碳氮磷化学计量分布格局及其驱动因素

理解植物叶片化学计量特征及其驱动因素对认识植物种群分布规律及预测植物对环境变化响应具有重要意义。该研究采集了青藏高原东缘针叶林84个样点共29种主要针叶树种叶片, 探讨该区域常绿针叶树种叶片碳(C)、氮(N)、磷(P)化学计量特征和分布格局及其驱动因素。结果表明: (1)在科和属水平上, 不同针叶树种叶片C、N含量和C:N差异显著; 叶片N:P < 14, 表明该区域针叶树种主要受N限制。(2)叶片N、P含量在环境梯度上表现出一致的分布规律: 均呈现出随纬度和海拔增加而显著降低, 随年平均气温(MAT)和年降水量(MAP)增加而显著增加的趋势; 而叶片C含量与纬度、海拔、MAT和MAP均未表现出显著相关性。(3)叶片C:N、C:P呈现出与N、P含量变化相反的分布格局: 均随纬度和海拔增加而显著增加, 随MAT和MAP增加而显著降低; 而叶片N:P与海拔、MAT和MAP均无显著相关性。(4)进一步分析表明, 叶片C、N、P含量及其化学计量比的主要驱动因素不尽相同。具体而言: 土壤特性是叶片C含量和N:P变异的主要驱动因子, 而叶片N、P含量和C:N、C:P的变异主要由气候因素决定。总之, 该区域针叶树种叶片化学计量沿环境梯度的变异规律有力地支持了温度生物地球化学假说, 在一定程度上丰富了对环境变化下植物叶片化学计量分布格局及其驱动机制的认识。     

Environmental signals from leaves--a physiognomic analysis of European vegetation

Leaf physiognomic traits vary predictably along climatic and environmental gradients. The relationships between leaf physiognomy and climate have been investigated on different continents, but so far an investigation based on European vegetation has been missing. A grid data set (0.5 degrees x 0.5 degrees latitude/longitude) has been compiled in order to determine spatial patterns of leaf physiognomy across Europe. Based on distribution maps of native European hardwoods, synthetic chorologic flora lists were compiled for all grid cells. Every synthetic chorologic flora was characterised by 25 leaf physiognomic traits and correlated with 16 climatic parameters. Clear spatial patterns of leaf physiognomy have been observed, which are statistically significant related to certain, temperature-related climate parameters. Transfer functions for several climatic parameters have been established, based on the observed relationships. The study provides evidence that synthetically generated floras represent a powerful tool for analysing spatial patterns of leaf physiognomy and their relationships to climate. The transfer functions from the European data set indicate slightly different relationships of leaf physiognomy and environment compared with results obtained from other continents.     

Leaf Shape Responds to Temperature but Not CO2 in Acer rubrum

The degree of leaf dissection and the presence of leaf teeth, along with tooth size and abundance, inversely correlate with mean annual temperature (MAT) across many plant communities. These relationships form the core of several methods for reconstructing MAT from fossils, yet the direct selection of temperature on tooth morphology has not been demonstrated experimentally. It is also not known if atmospheric CO₂ concentration affects leaf shape, limiting confidence in ancient climate reconstructions because CO₂ has varied widely on geologic timescales. Here I report the results of growing Acer rubrum (red maple) in growth cabinets at contrasting temperature and CO₂ conditions. The CO₂ treatment imparted no significant differences in leaf size and shape, while plants grown at cooler temperatures tended to have more teeth and more highly dissected leaves. These results provide direct evidence for the selection of temperature on leaf shape in one species, and support a key link in many leaf-climate methods. More broadly, these results increase confidence for using leaf shape in fossils to reconstruct paleoclimate.     

Correlations of climate and plant ecology to leaf size and shape: potential proxies for the fossil record

The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.     

Is there more insect folivory in warmer temperate climates? A latitudinal comparison of insect folivory in eastern North America

1.  It is generally believed that warmer climate forests suffer more herbivory, as a proportion of leaf area, than cooler climate forests. However, standardized studies using the same methodology have rarely been performed.
2.  We carried out a study on scattered forest-edge populations of four widespread tree species ( Quercus alba , Acer rubrum , Fagus grandifolia and Liquidambar styraciflua ) spanning 17° of latitude in North America.
3.  We sampled early summer sun leaves (12 weeks after bud break) at each latitude in 2 years. Total insect folivory damage was estimated from the percentage area damaged in fresh leaves on forest edges, using a scanner-linked software.
4.  The percentage area damage per leaf of all four species in both years shows a significant latitudinal trend, with less damage in lower latitude areas of eastern North America. This is contrary to what would generally be expected according to current ecological thinking. Among the four studied species, only A. rubrum showed a significant difference between the 2 years.
5.   Synthesis . The observation of an inverse latitudinal trend may have wider implications for the study of community functioning, suggesting that strength of 'biotic' interaction between plants and herbivores might actually be no less important, or in fact more important, in cool temperate climates compared with warm temperate climates.     

Spatiotemporal variation in leaf size and shape in response to climate

叶片的形态变异是研究植物响应气候变化的重要指标之一。叶片大小与形状影响着植物与外界环境的碳、水等物质交换和能量交换。然而,叶片大小与形状如何响应气候变化仍缺乏研究。此外,大多研究忽略了叶大小与形状在时间和空间上的种内变异,而只关注种间变异。我们收集了中国98年(1910-2008年)7个代表性双子叶植物的植物标本馆标本6000多份,并测量了它们叶片的叶长和宽度。我们探索了叶片大小(叶长、叶宽和长×宽乘积)的地理模式和时间趋势,(即研究了降水量和温度随时间和空间的变化对叶片大小和形状变化的影响。在控制了标本采集时间的影响后,全部物种的平均叶大小沿着纬度梯度的增加而减小,但这一关系在不同物种间存在差异。叶大小和形状的空间变异与温度和降水正相关。当控制了采集地点的影响后,全部物种的平均叶大小随着时间有变大的趋势。大多数物种叶大小的时间变化与降水正相关,而叶形状的时间变化则与温度正相关。我们的研究指出叶大小和形状在时空上的种内变异显著受气候的影响,同时说明植物标本可以为研究植物形态对气候变化的响应提供素材。     

Differences between tree species in hydraulic press calibration of leaf water potential are correlated with specific leaf area

Abstract To determine the usefulness of the J-14 Hydraulic Press (Campbell Scientific, Inc., Logan, Utah, U.S.A.) in estimating leaf water potential, we calibrated the J-14 Press against a Scholander-type pressure chamber for leaves of various tree species. The species tested were: Acer saccharum, Acer negundo, Acer rubrum. Populus tremuloides, Populus grandidentata, Quercus rubra, and Brassaia actinophylla (Schefflera). The regression calibrations were linear with standard errors about the regression less than 0.1 MPa. The regression equations for the four genera were significantly different, with the y- intercept increasing and the slope decreasing in order of decreasing specific leaf area (SLA). There were no significant differences between species of the calibration lines within the genera Acer and Populus. These data may indicate that leaves with lower SLA resist mechanical compression by the hydraulic press, causing the J-14 Press to be less sensitive to differences of leaf water potential. Therefore the J-14 Press is only a relative measure of leaf water status and does not measure leaf water potential.     

Plastic leaf morphology in three species of Quercus: The more exposed leaves are smaller,more lobated and denser

Phenotypic plasticity and developmental instability in leaf traits are common in oak species but the role of environmental factors is not well understood. To decipher possible correlations between different leaf traits and effects of the position of leaves within the tree canopy, we quantified the plasticity of three leaf traits of 30 trees of Quercus alba L., Quercus palustris Muench and Quercus velutina Lam. We hypothesized that trees could modify the shape of their leaves for better adaptation to the variable microclimate within the canopy. Our results demonstrated that the south and north outer leaves were significantly smaller, more lobed and denser than those situated in the inner canopy. The order of leaves on the branch accounted for the plasticity of leaf traits in Q. alba only. Plasticity of lobing in Q. alba and Q. velutina depended on the height of the trees. We detected fluctuating asymmetry (FA) in all three species, but the source of variation depended on branch position in Q. velutina only. FA was more pronounced in north-facing leaves. Plasticity of the leaf traits ranged from small to medium. Plasticity of leaf area and leaf mass per area (LMA) depended on the branch position. However, the plasticity of lobation was not affected by the location of a branch within the tree canopy. Quercus alba and Q. palustris had similar plastic responses but the plasticity of Q. velutina was significantly smaller. We concluded that individual plants detect and cope with environmental stress through vegetative organ modification.     

A climatic and taxonomic comparison between leaf litter and standing vegetation from a Florida swamp woodland

One method to determine past climate has been the use of leaf morphological characteristics of fossil leaves quantified using modern climate and canopy leaf characteristics. Fossil assemblages are composed of abscised leaves, and climate may be more accurately determined by using leaves from leaf litter instead of the canopy. To better understand whether taphonomic processes make a difference in this relationship, a north-central Florida woodland was sampled to determine the morphologically based climate estimates from these leaves. Leaves from woody, dicotyledonous plants were collected and identified, then compared using presence/absence data and analyzed using several linear regression equations and the CLAMP data set. Although the majority of standing vegetation was reflected in leaf litter, some inconsistencies were observed, which may reflect plant community structure or sampling technique. Mean annual temperature (MAT) and growing season precipitation (GSP) were estimated from leaf litter morphological characters and living leaves. Overall, values for MAT estimated from litter and living leaves were cooler than actual MATs, although several accurate and high estimates were obtained depending on the predictive method used. Estimated GSP values were higher than actual GSPs. Statistically, no difference was observed between MAT and GSP estimates derived from leaf litter vs. estimates derived from living leaves, with one exception.     

Variability in leaf optical properties among 26 species from a broad range of habitats

Leaves from 26 species with growth forms from annual herbs to trees were collected from open, intermediate, and shaded understory habitats in Mississippi and Kansas, USA. Leaf optical properties including reflectance, transmittance, and absorptance in visible and near infrared (NIR) wavelengths were measured along with leaf thickness and specific leaf mass (SLM). These leaf properties and internal light scattering have been reported to vary with light availability in studies that have focused on a limited number of species. Our objective was to determine whether these patterns in leaf optics and light availability were consistent when a greater number of species were evaluated. Leaf thickness and SLM varied by tenfold among species sampled, but within-habitat variance was high. Although there was a strong trend toward thicker leaves in open habitats, only SLM was significantly greater in open vs. understory habitats. In contrast, leaf optical properties were strikingly similar among habitats. Reflectance and reflectance/transmittance in the NIR were used to estimate internal light scattering and there were strong relationships (r1 > 0.65) between these optical properties and leaf thickness. We concluded that leaf thickness, which did not vary consistently among habitats, was the best predictor of NIR reflectance and internal light scattering. However, because carbon allocation to leaves was lower in understory species (low SLM) yet gross optical properties were similar among all habitats, the energy investment by shade leaves required to achieve optical equivalence with sun leaves was lower. Differences in leaf longevity and growth form within a habitat may help explain the lack of consistent patterns in leaf optics as the number of species sampled increases.     

Evolution of leaf form correlates with tropical-temperate transitions in Viburnum (Adoxaceae)

Strong latitudinal patterns in leaf form are well documented in floristic comparisons and palaeobotanical studies. However, there is little agreement about their functional significance; in fact, it is still unknown to what degree these patterns were generated by repeated evolutionary adaptation. We analysed leaf form in the woody angiosperm clade Viburnum (Adoxaceae) and document evolutionarily correlated shifts in leafing habit, leaf margin morphology, leaf shape and climate. Multiple independent shifts between tropical and temperate forest habitats have repeatedly been accompanied by a change between evergreen, elliptical leaves with entire margins and deciduous, more rounded leaves with toothed or lobed margins. These consistent shifts in Viburnum support repeated evolutionary adaptation as a major determinant of the global correlation between leaf form and mean annual temperature. Our results provide a new theoretical grounding for the inference of past climates using fossil leaf assemblages.