Inter- and intraspecific variation in grass phytolith shape and size: a geometric morphometrics perspective

Background and AimsThe relative contributions of inter- and intraspecific variation to phytolith shape and size have only been investigated in a limited number of studies. However, a detailed understanding of phytolith variation patterns among populations or even within a single plant specimen is of key importance for the correct taxonomic identification of grass taxa in fossil samples and for the reconstruction of vegetation and environmental conditions in the past. In this study, we used geometric morphometric analysis for the quantification of different sources of phytolith shape and size variation.MethodsWe used landmark-based geometric morphometric methods for the analysis of phytolith shapes in two extant grass species (Brachypodium pinnatum and B. sylvaticum). For each species, 1200 phytoliths were analysed from 12 leaves originating from six plants growing in three populations. Phytolith shape and size data were subjected to multivariate Procrustes analysis of variance (ANOVA), multivariate regression, principal component analysis and linear discriminant analysis.Key ResultsInterspecific variation largely outweighed intraspecific variation with respect to phytolith shape. Individual phytolith shapes were classified with 83 % accuracy into their respective species. Conversely, variation in phytolith shapes within species but among populations, possibly related to environmental heterogeneity, was comparatively low.ConclusionsOur results imply that phytolith shape relatively closely corresponds to the taxonomic identity of closely related grass species. Moreover, our methodological approach, applied here in phytolith analysis for the first time, enabled the quantification and separation of variation that is not related to species discrimination. Our findings strengthen the role of grass phytoliths in the reconstruction of past vegetation dynamics.     

Congener comparison of native (Zostera marina) and introduced (Z. japonica) eelgrass at multiple scales within a Pacific Northwest estuary

A congener comparison of native (Zostera marina) and introduced (Zostera japonica) eelgrasses was conducted in Willapa Bay, Washington, USA. Along intertidal transects, Z. japonica (0.1–1.5 m above mean lower low water [MLLW]) occurred above Z. marina (<0.6 m MLLW). Both species declined in shoot length at higher elevation, but Z. japonica was always shorter (20 vs. 100 cm) and occurred at higher shoot density (>3,800 vs. <360 m^?2 in Z. marina). Z. japonica exhibited greater seasonal variation in biomass, with increases supported by both sustained asexual reproduction (rhizome branching) and recruitment from seeds (30 vs. <5% in Z. marina). Z. japonica’s successful invasion appears related to small size and high reproductive output, allowing it to spread quickly in a variable and stressful intertidal environment where competitive effects are low. Based on interannual changes in abundance, the native eelgrass has also recently increased in Willapa Bay, and one hypothesis involves “engineering” of suitable habitat at higher tidal elevations by Z. japonica.     

Fossil plant evidence for Early and Middle Jurassic paleoenvironmental changes in Lanzhou area, Northwest China

Estimating the paleoclimate changes through CO₂ levels has become a promising area of geological research. This paper focuses on analysis of fossil Ginkgo in continuous sedimentary series in northwestern China using plant anatomy and organic geochemistry approaches. The CO₂ variation curve during Early and Middle Jurassic is reconstructed based on the stomatal ratio method, which is consistent with the estimated results of GEOCARB III. In comparison with the carbon isotopic composition measured from the fossil leaves of Ginkgo, we suggest that the stomata-based CO₂ concentrations for the Jurassic are generally consistent with the predictions of the geochemical model, ranging from 1000 to 1600 ppmv. Measurements of carbon isotope values demonstrate that the water use efficiency of the fossil Ginkgo in a “green house” world is higher than that of the living Ginkgo. Investigations of physiological responses of plants to the increasing CO₂ level at the present and in the future should help demonstrate this effect. The cause of the carbon isotopic shift at the boundary between Aalenian and Bajocian for the Yaojie Basin is unclear and therefore needs further investigation.     

Wood Anatomy Reveals High Theoretical Hydraulic Conductivity and Low Resistance to Vessel Implosion in a Cretaceous Fossil Forest from Northern Mexico

The Olmos Formation (upper Campanian), with over 60 angiosperm leaf morphotypes, is Mexico''s richest Cretaceous flora. Paleoclimate leaf physiognomy estimates indicate that the Olmos paleoforest grew under wet and warm conditions, similar to those present in modern tropical rainforests. Leaf surface area, tree size and climate reconstructions suggest that this was a highly productive system. Efficient carbon fixation requires hydraulic efficiency to meet the evaporative demands of the photosynthetic surface, but it comes at the expense of increased risk of drought-induced cavitation. Here we tested the hypothesis that the Olmos paleoforest had high hydraulic efficiency, but was prone to cavitation. We characterized the hydraulic properties of the Olmos paleoforest using theoretical conductivity (K_s), vessel composition (S) and vessel fraction (F), and measured drought resistance using vessel implosion resistance and the water potential at which there is 50% loss of hydraulic conductivity (P₅₀). We found that the Olmos paleoforest had high hydraulic efficiency, similar to that present in several extant tropical-wet or semi-deciduous forest communities. Remarkably, the fossil flora had the lowest , which, together with low median P₅₀ (−1.9 MPa), indicate that the Olmos paleoforest species were extremely vulnerable to drought-induced cavitation. Our findings support paleoclimate inferences from leaf physiognomy and paleoclimatic models suggesting it represented a highly productive wet tropical rainforest. Our results also indicate that the Olmos Formation plants had a large range of water conduction strategies, but more restricted variation in cavitation resistance. These straightforward methods for measuring hydraulic properties, used herein for the first time, can provide useful information on the ecological strategies of paleofloras and on temporal shifts in ecological function of fossil forests chronosequences.     

延河流域植物群落功能性状对环境梯度的响应

研究群落水平上的植物功能性状特征及其随环境梯度的变化规律,对认识不同环境梯度下植物群落的形成及其对环境的适应机制具有重要意义。以延河流域不同环境梯度下的稳定的自然植物群落为对象,测量了植物群落组成物种的叶厚度、比叶面积、叶组织密度、比根长、根组织密度、单位质量叶氮含量、单位质量根氮含量、种子质量、种子体积等9个性状,然后以物种重要值为基础加权平均得到各个性状在群落水平上的平均值(即群落性状值);以现有的环境因子栅格图为基础,利用ArcGIS提出各群落对应的环境因子值,同时测定各个群落的土壤水分,分析群落各性状值与环境因子的关系,并建立关系模型。结果表明:在群落水平上,9个植物功能性状分别与13个环境因子存在不同程度的相关性,同时这9个植物功能性状对8个环境因子梯度(土壤水分、年4-10月平均气温、年7-9月总降雨量、降雨季节变化、年平均降雨量、年平均蒸发量、坡度、坡向)的响应特征较好,不同植物功能性状间具有较好相关性。群落水平上植物功能性状及其组合随环境梯度的规律性变化,反映了延河流域植被群落构建过程中环境对功能性状的筛选效应。该研究结果对该区的植被恢复重建的物种选择及植被布局规划具有重要的实践意义。     

Morphologic and taxonomic relationships of the Psilotaceae relative to evolutionary lines in early land vascular plants

Examination of the fossil record shows that there is no direct evidence regarding the origins and early evolution of the Psilotaceae. Past comparisons betweenPsilotum orTmesipteris and certain fossil plants are reviewed. The major types of early land vascular plants are surveyed in order to demonstrate their basic characteristics and evolutionary trends and to point out the absence of any direct links with the Psilotaceae. Fossil plants of problematical affinities which appear to be important in the early diversification of ferns or plants closely related to ferns are discussed. The nature of stem-leaf relationships of some primitive, extant filicalean ferns and possibly the Psilotaceae is considered in terms of possible similar occurrences among fossil plants.     

Fossil Woods from Late Cretaceous of Heilongjiang Province,Northeast China,and Their Palaeoenviromental Implications

Three species of fossil coniferous woods, Cupressinoxylon jiayinense Wang R. F., Wang Y. F. et Chen Y. Z., Taxodioxylon cryptomeria Schonfeld and Protopiceoxylon amurense Du N. Z. from late Cretaceous of Heilongjiang Province,Northeast China, were described. Their wood structural characters showed their affinities to the extant Cupressus, Cryptomeria and Keteleeria respectively. The data from fossil woods, fossil foliage and pollen assemblage of late Cretaceous in the same region showed that the flora consists of conifers and broad-leaved trees and most elements were subtropic or warm-temperate, only a few of them were temperate vegetation. At the same time, the occurrence of fungi filaments in the wood of Cupressinoxylon fiayinense might suggest a type of humid and warm environment. All of these evidences indicated that a humid warm temperate or subtropic paleoclimate had existed in Heilongjiang Province during Late Cretaceous.     

Ecological distribution of Cenomanian terrestrial plants based on 13C/12C ratios

The Cenomanian lagoonal member of the `Argiles du Baugeois' (Anjou, France) yielded a rich and exceptionally well-preserved fossil leaf flora. Stable carbon isotope ratios of fossil plants were measured in order to investigate the presence of a palaeoenvironmental signal. The small intraspecies variations of δ<sup>13</sup>C values observed for most of the fossil leaves suggested that the isotopic signal had not been significantly altered. Hence, an isotopic approach was used as an attempt to assist in reconstructing the ecological distribution of the flora. The <sup>13</sup>C-enrichment of the fossil leaves suggested that the plants underwent water or salt stress. The occurrence of the conifer Frenelopsis suggested, at least locally, a saline environment such as a lagoon. According to their decreasing δ<sup>13</sup>C values, all the plants collected could have been distributed along a decreasing salinity transect from the lagoon to a flood plain. The predominant species, Eretmophyllum andegavense, a fossil ginkgo, exhibited a wide range of δ<sup>13</sup>C values. This could indicate that this taxon grew in a wide range of habitats with varying salinities. The origin of the organic matter appeared to be terrestrial with a major contribution from water-stressed plants such as Frenelopsis, as suggested by the similarity between δ<sup>13</sup>C values of the conifer and the sedimentary organic matter. δ<sup>13</sup>C values of the sediment indicated stable palaeoenvironmental conditions during the deposition of the `Argiles du Baugeois' member. Hence, while detailed palaeovegetation reconstructions are generally limited to the few deposits which present in-situ palaeoflora, the contribution of isotope geochemistry could allow reconstructions for a wider range of fossil plant deposits.     

Abundance and dispersion of the invasive Mediterranean annual, Centaurea melitensis in its native and non-native ranges

In general, invasive plants are assumed to behave more aggressively in their invasive ranges than in their native range, and studies of the mechanisms of invasion often assume these differences. However, comparisons of abundances between native and invasive ranges are rarely carried out. We compared density and dispersion of the invasive plant, Centaurea melitensis (Asteraceae) in its native range and two invasive ranges of similar mediterranean-climate type. The objective was to quantify the differences in its abundance among three distant regions. We surveyed six sites in the native range (Spain) and in each of two invaded ranges (California and central Chile) for population density, relative dominance and spatial distribution of Centaurea. Centaurea occurred at higher densities in invasive sites than in native ones, with a median of 100 plants per m² and 70 plants per m² in California and Chile, respectively, compared to only 4 plants per m² in Spain. Centaurea was more dominant in both invasive ranges than in the native range. Centaurea density and relative dominance were highly variable within regions. Plants in Spain were randomly dispersed, while those in both invasive ranges were more aggregated. Annual precipitation and mean annual temperature were the best predictors of Centaurea density. In California sites, density was negatively correlated with soil nutrients. The presence of at least one high-density population with near total dominance in Spain suggests that there might be ecological mechanisms for invasiveness in Centuarea that are not unique to invaded ranges.     

Molecular Variation of Satellite DNAβ Molecules Associated with Malvastrum yellow vein virus and Their Role in Pathogenicity

Previous studies have found that the diversity of begomovirus-associated DNAβ satellites is related to host and geographical origin. In this study, we have cloned and sequenced 20 different isolates of DNAβ molecules associated with Malvastrum yellow vein virus (MYVV) isolated from Malvastrum coromandelianum plants in different geographical locations of Yunnan Province, China. Analyses of their molecular variation indicate that the satellites are clustered together according to their geographical location but that they have only limited sequence diversity. Infectivity tests using infectious clones of MYVV and its associated DNAβ molecule indicate that MYVV DNAβ is indispensable for symptom induction in Nicotiana benthamiana, N. glutinosa, Petunia hybrida, and M. coromandelianum plants. Furthermore, we showed that MYVV interacts functionally with heterologous DNAβ molecules in N. benthamiana plants.     

Growth of tissue culture–regenerated salt marsh monocots in a simulated marsh field plot: Implication for wetland creation and restoration

Phenotypically and genetically variable salt marsh plants are needed for wetland creation and restoration efforts. Selected tissue culture regenerants of five salt marsh monocots, Spartina patens, Spartina alterniflora, Juncus gerardi, Juncus roemerianus, and Scirpus robustus, were planted in a simulated marsh field plot that was flood-irrigated with 10 ppt salt water to compare their phenotypic variation for potential use in wetland projects. Plant growth was evaluated after one growing season. Phenotypic variation among regenerants was found in S. alterniflora, S. patens and J. gerardi, indicating the occurrence of somaclonal variation. In S. alterniflora, significant differences occurred among regenerants in stem density. In J. gerardi, significant differences occurred in height and clone circumference. In S. patens, two of the nine regenerants exhibited higher biomass and stem density than some of the other regenerants. By using the random amplified polymorphic DNA (RAPD) technique, genome DNA variation in S. patens regenerants was detected. Genetic variation not only occurred among phenotypically different regenerants, but also among those phenotypically similar for the characteristics measured. Tissue culture–regenerated plants often have desirable genetic characteristics and adaptability as a result of somaclonal variation and may enable a species to perform its ecological functions in created or restored wetlands where ideal environments cannot be achieved. Thus, some previously unrestorable sites may be restorable or marginal marshes made more productive.     

闽楠叶形态与叶脉网络性状关系对城市生长环境的响应

植物叶形态与叶脉网络功能性状的协同变异与权衡关系,对深入理解植物叶脉网络功能性状对环境变异的生态适应,以及预测植物物种生活习性对城市化过程的响应具有重要意义。闽楠作为珍贵的常绿阔叶树种,正在城市绿化中逐步推广。针对不同生长环境中（行道与植物园混交林）的闽楠,开展了叶形态与叶脉网络功能性状关系对城市生长环境的响应研究。研究结果表明：闽楠叶性状值基本满足正态分布,各性状变异系数保持在10%-20%之间,群体内性状变异较为丰富,单因素方差分析表明两种环境对叶形态性状的影响比叶脉网络系统的影响更明显;两种生长环境下闽楠叶形态性状组与叶脉网络功能性状组都具有极显著相关性,行道和植物园混交林典型性相关系数分别为0.804和0.795,叶形态性状与叶脉直径呈显著正相关,形态性状、叶脉直径与初级脉密度呈显著负相关;闽楠在响应城市生长环境的过程中呈现出相应的经济权衡机制,行道环境中闽楠以较大的初级脉密度和较小叶面积来确保水分获取和光合之间的平衡,植物园闽楠则采用较低初级叶脉密度、较高叶面积和叶脉直径的叶形态和叶脉网络构建模式。在选择闽楠作为城市绿化树种时,可将叶片形态性状组与叶脉网络功能性状组的协同变化和权衡关系作为选种依据,以提高闽楠在城市环境中的成活率和适应性。     

A new species of Baiera from the Early Cretaceous Jehol Biota of southeastern Jilin,China

The Early Cretaceous Yingzuilazi Formation is exposed in the Baishan Basin, Baishan region of the southeastern Jilin Province, China. So far, no reports on fossil plants from this formation have been published. During recent field excursions, abundant faunal remains belonging to the Early Cretaceous Lycoptera–Ephemeropsis–Eosestheria assemblage of the Jehol Biota and numerous fossil plants were collected from the lacustrine beds of the lower part of this formation. A new species of Ginkgoales from this formation, Baiera baishanensis n. sp., is described based upon the leaf morphology and epidermal characters. This is the first report about fossil plants from the Yinzuilazi Formation, the easternmost distribution area of the Jehol Biota. The discovery of the new species extends significantly the stratigraphic and geographic distribution of Baiera in the Early Cretaceous Jehol Biota as well as the Eurasia. It also shows that Baiera was a common member of Ginkgophytes once lived in the Early Cretaceous deciduous forest of Northeast China. The new species also improves our knowledge on understanding the leaf morphology, epidermal features, and diversity of Baiera during the Early Cretaceous. Analysis of the epidermal characters of the new species and other associated plants reveals that the plants grew in a warm and humid climate in the temperate zone. The presence of some deciduous plants, including gingkgoaleans, czekanowskialeans, and some conifers, demonstrates a climate with seasonal fluctuations and precipitation.     

Photosynthetic responses to temperature of two tropical rainforest tree species from Costa Rica

Annual mean temperature increases will cause alterations in many ecosystem processes, which affect plants given their physiological sensitivity to temperature. That is closely related with plant growing conditions, genotype and plasticity. We studied the photosynthetic responses to instantaneous temperature changes and functional leaf traits in two tropical tree species associated with different successional positions, Zygia longifolia (early successional) and Dipteryx oleifera (late successional), in the northern lowlands of Costa Rica. We found that D. oleifera had thicker leaves and lower stomatal density, but similar specific leaf area to Z. longifolia. Maximum photosynthetic rate (A _max) and maximum RuBP saturate rate of carboxylation were higher in Z. longifolia than in D. oleifera. At 37 °C, only Z. longifolia reduced A _max and water use efficiency (WUE). But D. panamensis presented more severe effects on the quantum yield, respiration and light compensation points. The temperature response curves showed a similar optimum temperature near 27 °C for both species. On the other hand, the low and high temperature compensation points were different, with D. oleifera showing a narrower range than Z. longifolia. As a whole, we found two different strategies to avoid temperature stress: one reducing WUE (Z. longifolia), and the other one increasing metabolic rates (D. oleifera). However, the ability to withstand stressful situations may, in a larger context, negatively affect ecosystem water and carbon fluxes. Also, functional plasticity in response to temperature changes may relatively affect the ecosystem by causing long-term variations in their representation within the complex diversity mosaic of their forest habitats.     

Occurrence of an in situ fern grove in the Aptian Douiret Formation, Tataouine area, South-Tunisia

A level with fern stumps was discovered in the Aptian Douiret Formation, South-Tunisia. These stumps are preserved as external moulds or casts, without any preservation of anatomical structures. These stumps are considered to be affiliated with the numerous fossil plants assigned to the fern genera Alstaettia and Piazopteris that are widely distributed in coeval strata from the same region, either as leaf imprints or as permineralized remains. The record of in situ fossil forests for the Southern Hemisphere reveals that their systematic components are different, i.e. mainly corystosperms and/or conifers, and rarely under tidal influence. The way this fern grove settled in a margino-littoral environment is discussed.     

Environmental Heterogeneity and Population Differentiation in Plasticity to Drought in <Emphasis Type="Italic">Convolvulus Chilensis</Emphasis> (Convolvulaceae)

Plant populations may show differentiation in phenotypic plasticity, and theory predicts that greater levels of environmental heterogeneity should select for higher magnitudes of phenotypic plasticity. We evaluated phenotypic responses to reduced soil moisture in plants of Convolvulus chilensis grown in a greenhouse from seeds collected in three natural populations that differ in environmental heterogeneity (precipitation regime). Among several morphological and ecophysiological traits evaluated, only four traits showed differentiation among populations in plasticity to soil moisture: leaf area, leaf shape, leaf area ratio (LAR), and foliar trichome density. In all of these traits plasticity to drought was greatest in plants from the population with the highest interannual variation in precipitation. We further tested the adaptive nature of these plastic responses by evaluating the relationship between phenotypic traits and total biomass, as a proxy for plant fitness, in the low water environment. Foliar trichome density appears to be the only trait that shows adaptive patterns of plasticity to drought. Plants from populations showing plasticity had higher trichome density when growing in soils with reduced moisture, and foliar trichome density was positively associated with total biomass. Co-ordinating editor: F. Stuefer     

Patterns of Plant Biomass Allocation in Temperate Grasslands across a 2500-km Transect in Northern China

Plant biomass allocation between below- and above-ground parts can actively adapt to the ambient growth conditions and is a key parameter for estimating terrestrial ecosystem carbon (C) stocks. To investigate how climatic variations affect patterns of plant biomass allocation, we sampled 548 plants belonging to four dominant genera (Stipa spp., Cleistogenes spp., Agropyron spp., and Leymus spp.) along a large-scale (2500 km) climatic gradient across the temperate grasslands from west to east in northern China. Our results showed that Leymus spp. had the lowest root/shoot ratios among the each genus. Root/shoot ratios of each genera were positively correlated with mean annual temperature (MAT), and negatively correlated with mean annual precipitation (MAP) across the transect. Temperature contributed more to the variation of root/shoot ratios than precipitation for Cleistogenes spp. (C4 plants), whereas precipitation exerted a stronger influence than temperature on their variations for the other three genera (C3 plants). From east to west, investment of C into the belowground parts increased as precipitation decreased while temperature increased. Such changes in biomass allocation patterns in response to climatic factors may alter the competition regimes among co-existing plants, resulting in changes in community composition, structure and ecosystem functions. Our results suggested that future climate change would have great impact on C allocation and storage, as well as C turnover in the grassland ecosystems in northern China.     

Natural variation for drought-response traits in the Mimulus guttatus species complex

Soil moisture is a key factor affecting plant abundance and distribution, both across and within species. In response to water limitation, plants have evolved numerous morphological, physiological, and phenological adaptations. In both well-watered and water-limited conditions, we identified considerable natural variation in drought-related whole-plant and leaf-level traits among closely related members of the Mimulus guttatus species complex that occupy a diversity of habitats in the field. The self-fertilizing Mimulus nasutus and serpentine-endemic Mimulus nudatus demonstrated the overall greatest tolerance to soil water limitation, exhibiting the smallest reduction in seed set relative to well-watered conditions. This may be due in part to early flowering, faster fruit development, and low stomatal density. In contrast, flowering of coastal M. guttatus was so delayed that it precluded any seed production in water-limited conditions. This range of phenotypic responses to soil water deficit in Mimulus, coupled with developing genomic resources, holds considerable promise for identifying genomic variation responsible for adaptive responses to soil water availability.     

Fossil leaves of Buxus (Buxaceae) from the Upper Pliocene of Yunnan,SW China

A new species, Buxus pliosinica H.S. Huang, T. Su et Z.K. Zhou n. sp. (Buxaceae) is designated based on leaf architecture and cuticular features of five compressed fossil leaves from the Upper Pliocene Sanying Formation of Yunnan, SW China. Leaves of B. pliosinica are elliptic and small, with entire margin, retuse tip, intramarginal vein, and exmedially ramified tertiary veins. The leaves are hypostomatic with anomocytic stomatal apparatuses and giant stomata. Based on comparisons of leaf morphological and cuticular features, B. sempervirens Linnaeus is considered as the nearest living relative of B. pliosinica. Morphologically, these species share similar elliptic shape and size, cuneate base, retuse tip, similar ranges of petiole length, angles of 2° vein to midvein, and distance from the intramarginal vein to the margin. In terms of cuticular features, they are similar in type of stomatal apparatus, maximum length of giant stomata and range of stomatal length, but differ in the presence of indumentum. This discovery represents the first fossil record of Buxus from the SE margin of the Tibetan Plateau, and confirms the existence of Buxus in this region by the late Pliocene. Meanwhile, the newly described fossil species contributes to our understanding of the evolution of extant Buxus.