Reconstitution d'un « paysage de l'époque houillère » revue à la lumière des découvertes récentes sur les cuticules végétales fossiles

To date, plants with a climbing or scrambling growth habit are widely represented in equatorial forest ecosystems, with a warm and humid climate, with a variety of different species. Although it has been speculated repeatedly that several Late Carboniferous seed ferns applied the same growth strategies as modern vines and /or lianas, only few examples have been substantiated in sufficient details. Most Paleozoic seed ferns are reconstructed as free-growing erect trees. However, these last years, new discoveries about the growth habits of fossil plants have been highlighted on the basis of cuticular material. In this way, different types of climbing organs of seed ferns, reported on pteridosperm cuticles collected from the Stephanian basin of the Blanzy-Montceau (central France), have revolutionized the stereotype of “free-growing erect trees” that we had about these plants. These discoveries demonstrate the potential of cuticular analysis for the reconstruction of growth habits of fossil plants. Moreover they exemplify that climbing and scrambling became common life strategies among Late Carboniferous seed ferns. The increasing proportion of climbing seed ferns in the Stephanian, interpreted as an expression of changing structures of Late Paleozoic coal swamp forests, lead to modify the “classical” reconstructions of the Late Carboniferous landscapes.     

The callistophytales (Pteridospermopsida): Reproductively sophisticated paleozoic gymnosperms

The Callistophytales nov. order is proposed for a small family of Pennsylvanian and possibly Permian pteridosperms. Plants conform to two species of Callistophyton and their reproductive organs. The small, eustelic sporophytes have a scrambling, shrub-like habit, profuse branching, adventitious roots and pinnately compound fern-like leaves with sphenopterid pinnules. Reproductive organs are borne on the abaxial surface of the pinnules, and consist of cardiocarpalean ovules and synangiate pollen organs with saccate pollen. Gametophyte development and reproductive biology conform closely to those of extant gymnosperms in the Coniferales. Anatomically preserved reproductive organs of the major groups of Paleozoic gymnosperms are compared, and a closer than currently recognized relationship of Paleozoic seed plants is proposed.     

Remains of secretory cavities in pinnules of Stephanian pteridosperms from Blanzy-Montceau (Central France): a comparative study

Remains of secretory cavities, so-called resin or secretion bodies, in pinnules of Stephanian pteridosperms from the Blanzy-Montceau Basin (Central France) are examined from cuticles of four species: Dicksonites leptophylla, D. pluckenetii, Pseudomanopteris paleaui , and P. ribeyronii . The distribution of the secretion bodies in pinnules may be (1) simple and in consistent patterns, (2) random, but topographically unequal, or (3) completely random. Differences in the morphology of the bodies may be related to different modes of development of the secretory cavities, i.e. schizogenous or (schizo-) lysigenous development. The value of using these features in fossil plant taxonomy is discussed. Finally, some comments on possible ecological functions of the secretion of lipophilic substances in pteridosperm pinnules are suggested. The secretion of lipophilic substances is abundant among taxa with a vine-like life-form, and this may be related to special demands on protection of climbing or scrambling plants.     

Developmental plasticity and biomechanics of treelets and lianas in Manihot aff. quinquepartita (Euphorbiaceae): a branch-angle climber of French Guiana

Background and Aims

Most tropical lianas have specialized organs of attachment such as twining stems, hooks or tendrils but some do not. Many climbers also have an early self-supporting phase of growth and in some species this can produce treelet-sized individuals. This study focuses on how a liana can climb without specialized attachment organs and how biomechanical properties of the stem are modulated between self-supporting treelets and canopy-climbing lianas.

Methods

Biomechanics and stem development were investigated in self-supporting to climbing individuals of Manihot aff. quinquepartita (Euphorbiaceae) from tropical rain forest at Saül, central French Guiana. Bending tests were carried out close to the site of growth. Mechanical properties, including Young''s elastic modulus, were observed with reference to habit type and changes in stem anatomy during development.

Key Results

This liana species can show a remarkably long phase of self-supporting growth as treelets with stiff, juvenile wood characterizing the branches and main stem. During the early phase of climbing, stiff but unstable stem segments are loosely held in a vertical position to host plants via petiole bases. The stiffest stems – those having the highest values of Young''s modulus measured in bending – belonged to young, leaning and climbing stems. Only when climbing stems are securely anchored into the surrounding vegetation by a system of wide-angled branches, does the plant develop highly flexible stem properties. As in many specialized lianas, the change in stiffness is linked to the development of wood with numerous large vessels and thin-walled fibres.

Conclusions

Some angiosperms can develop highly effective climbing behaviour and specialized flexible stems without highly specialized organs of attachment. This is linked to a high degree of developmental plasticity in early stages of growth. Young individuals in either open or closed marginal forest conditions can grow as substantial treelets or as leaning/climbing plants, depending on the availability of host supports. The species of liana studied differs both in terms of development and biomechanics from many other lianas that climb via twining, tendrils or other specialized attachment organs.Key words: Biomechanics, bending, developmental plasticity, French Guiana, liana, Manihot aff. quinquepartita (Euphorbiaceae), treelet, branch angle climber, Young''s modulus     

Evolutionary,genetic, environmental and hormonal-induced plasticity in the fate of organs arising from axillary meristems in Passiflora spp.

Tendrils can be found in different plant species. In legumes such as pea, tendrils are modified leaves produced by the vegetative meristem but in the grape vine, a same meristem is used to either form a tendril or an inflorescence. Passiflora species originated in ecosystems in which there is dense vegetation and competition for light. Thus climbing on other plants in order to reach regions with higher light using tendrils is an adaptive advantage. In Passiflora species, after a juvenile phase, every leaf has a subtending vegetative meristem, and a separate meristem that forms both flowers and a tendril. Thus, flowers are formed once a tendril is formed yet whether or not this flower will reach bloom depends on the environment. For example, in Passiflora edulis flowers do not develop under shaded conditions, so that tendrils are needed to bring the plant to positions were flowers can develop. This separate meristem generally forms a single tendril in different Passiflora species yet the number and position of flowers formed from the same meristem diverges among species. Here we display the variation among species as well as variation within a single species, P. edulis. We also show that the number of flowers within a specific genotype can be modulated by applying Cytokinins. Finally, this separate meristem is capable of transforming into a leaf-producing meristem under specific environmental conditions. Thus, behind what appears to be a species-specific rigid program regarding the fate of this meristem, our study helps to reveal a plasticity normally restrained by genetic, hormonal and environmental constraints.     

Dioecy and its correlates in the flowering plants

Considerable effort has been spent documenting correlations between dioecy and various ecological and morphological traits for the purpose of testing hypotheses about conditions that favor dioecy. The data analyzed in these studies, with few exceptions, come from local floras, within which it was possible to contrast the subsets of dioecious and nondioecious taxa with regard to the traits in question. However, if there is a strong phylogenetic component to the presence or absence of dioecy, regional sampling may result in spurious associations. Here, we report results of a categorical multivariate analysis of the strengths of various associations of dioecy with other traits over all flowering plants. Families were scored for presence of absence of monoecy or dioecy, systematic position, numbers of species and genera, growth forms, modes of pollination and dispersal, geographic distribution, and trophic status. Seven percent of angiosperm genera (959 of 13,500) contain at least some dioecious species, and ≈6% of angiosperm species (14,620 of 240,000) are dioecious. The most consistent associations in the data set relate the presence of dioecy to monoecy, wind or water pollination, and climbing growth. At both the family and the genus level, insect pollination is underrepresented among dioecious plants. At the family level, a positive correlation between dioecy and woody growth results primarily from the association between dioecy and climbing growth (whether woody or herbaceous) because neither the tree nor the shrub growth forms alone are consistently correlated with a family's tendency to include dioecious members. Dioecy appears to have evolved most frequently via monoecy, perhaps through divergent adjustments of floral sex ratios between individual plants. Monoecy itself is related to abiotic pollination and climbing growth as revealed by multivariate analysis. Dioecy and monoecy are concentrated in the less advanced superorders of Thorne (1992) and subclasses of Cronquist (1988). The frequency of dioecy found in a local flora therefore reflects the level of dioecy in its particular pool of families as much as, or more than, local selective factors. The positive associations of dioecy with abiotic pollination and monoecy are related to floral developmental and morphological attributes, as is the negative association with bird and bat pollination; the positive association of dioecy with climbing growth is tentatively explained in terms of differential selection for optimal resource allocation to sexual function. If rapid upward growth is at a premium in climbers and if fruit set at least temporarily inhibits growth or requires the production of thicker, more slowly growing stems to support heavy fruits, it might be advantageous to postpone femaleness. If the effect is strong, this may favor male plants.     

Gelatinous fibers are widespread in coiling tendrils and twining vines

Although the coiling of tendrils and the twining of vines has been investigated since Darwin's time, a full understanding of the mechanism(s) of this coiling and twining ability has not yet been obtained. In a previous study (Planta 225: 485-498), gelatinous (G) fibers in tendrils of redvine occurred concomitantly with the ability to coil, strongly indicating their role in the coiling process. In this study, tendrils and twining vines of a number of species were examined using microscopic and immunocytochemical techniques to determine if a similar presence and distribution of these fibers exists in other plant species. Tendrils that coiled in many different directions had a cylinder of cortical G fibers, similar to redvine. However, tendrils that coiled only in a single direction had gelatinous fibers only along the inner surface of the coil. In tendrils with adhesive tips, the gelatinous fibers occurred in the central/core region of the tendril. Coiling occurred later in development in these tendrils, after the adhesive pad had attached. In twining stems, G fibers were not observed during the rapid circumnutation stage, but were found at later stages when the vine's position was fixed, generally one or two nodes below the node still circumnutating. The number and extent of fiber development correlated roughly with the amount of torsion required for the vine to ascend a support. In contrast, species that use adventitious roots for climbing or were trailing/scrambling-type vines did not have G fibers. These data strongly support the concept that coiling and twining in vines is caused by the presence of G fibers.     

川西亚高山冷杉林枯枝落叶层的群落学作用

冷杉林每年凋落物量(干重)0.5—4.0吨／公顷,枯枝落叶层(Ao层)干重总量每公顷40吨左右。本文通过观测和实验,探讨了冷杉林Ao层物质循环格式及其在生态系统中的养分和水分循环的特殊重要作用,以及对群落中的植物分布、生长发育的影响。     

Functional strategies and distribution of climbing plant communities in different vegetation patches in a subtropical dry forest,central Argentina

Aims In the context of global change, the impacts of forest structure alteration on climbing plants in extra-tropical ecosystems are poorly understood. It also remains little explored, the functional strategies among climbing plant species and its relationship with the local-scale distribution of climbing plant communities. Here, we aimed at three goals: (i) we studied how climbing plant community composition responds to the modification of the original forest structure in a subtropical dry forest; (ii) we characterized climbing plant species according to functional traits related to the acquisition and use of resources; and (iii) we examined whether functional strategies at the community level are also responding to vegetation structure change, a much less addressed topic in the ecology of climbing plants.     

氮磷添加对树木生长和森林生产力影响的研究进展

人为活动所导致的氮、磷输入和大气氮、磷沉降使生态系统中的氮、磷可利用性大幅提高, 对陆地生态系统的碳循环过程产生了显著影响。树木生长和森林生产力在全球碳循环中发挥着重要作用, 它决定着陆地碳固存的大小和方向。目前, 在全球范围内开展了很多氮、磷添加调控树木生长和森林生产力的野外控制实验, 但是研究结果并不一致, 受到多种生物、环境和实验处理条件等因素的影响。该文从野外氮添加和磷添加实验的文献数量、实验数量及其全球空间分布三个方面概述了氮、磷添加对树木生长和森林生产力影响的研究现状, 并总结了氮、磷添加实验中树木生长和森林生产力的评估方法, 包括相对生长速率和绝对增长量。基于相关的研究结果, 阐述了氮、磷添加影响树木生长和森林生产力的调控因素及其潜在影响机制, 包括气候、树木径级与林龄、植物功能性状(共生菌根类型、树木固氮属性和保守性与获得性性状)、植物和微生物相互作用关系、区域养分沉降速率和实验处理条件等。最后, 基于当前的研究进行了系统总结, 并指出今后需要加强的几个方面的研究, 以期为后续研究提供参考: 树木生长响应氮、磷添加的生理学机制, 树木各部分生长对氮、磷添加响应的权衡与分配, 植物功能性状在调节与预测树木生长响应氮、磷添加中的作用, 树木之间的竞争关系如何调控氮、磷添加对树木生长的影响, 以及开展长期的和联网的氮、磷添加对树木生长和森林生产力影响的野外控制实验。     

Cuticles of Mariopteris occidentalis White nov. emend. from the Middle Pennsylvanian of Oklahoma (USA), and a new type of climber hook for mariopteroid pteridosperms

Cuticles of Mariopteris occidentalis are described from the Desmoinesian (Middle Pennsylvanian) of Oklahoma (USA). This species, like other mariopteroids, had a vine- to liana-like growth habit and climbed with specialized climber hooks. However, M. occidentalis is different from other mariopteroids in having small recurved hooks on the abaxial surfaces of the pinna axes. The diagnosis for M. occidentalis White 1899 is emended based on additional macroscopical observations and data on the epidermal anatomy; a lectotype is designated. M. occidentalis is compared with Pseudomariopteris cordato-ovata from the Stephanian and Autunian of Europe and North America, a taxon which is considered very similar and may be related. Although the two taxa indeed display similarities, significant evidence for a closer relationship could not be found. Finally, some features, e.g. marginal water pits and the stomatal structure, are considered with regard to their palaeoautecological significance where they are interpreted as adaptations to special physiological requirements of a vine- to liana-like life form.     

森林生态系统硅素循环研究进展

硅是植物生长发育的有益元素,其在生态系统内的迁移转化是维持生态系统结构与功能的决定性因素之一。近年来,陆地生态系统硅循环特别森林生态系统硅循环在全球生物地球化学循环中的重要性,受到越来越多的关注。该文总结了国内外森林生态系统硅循环研究的成果,在综述了硅在森林生态系统中的存在形态、分布、循环过程的基础上,总结了森林生态系统硅循环的特点、作用及其影响因素,并指出典型森林生态系统类型中硅循环规律的研究、森林生态系统与其它生态系统硅循环的比较研究、森林生态系统硅循环对全球气候变化的影响和响应研究和人类干扰对森林生态系统硅循环的影响的研究将是今后开展森林生态系统硅循环研究的重点。     

A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems

Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth and forest productivity, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and forest productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and forest productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.     

Tropical Vine Growth and the Effects on Forest Succession: A Review of the Ecology and Management of Tropical Climbing Plants

The climbing habit has evolved independently in many plant taxa, offering vines the ability to compete with non-climbing vegetation for resources such as light, nutrients, and water. This review examines the structural and functional characteristics that allow climbing plants to (1) achieve widespread dispersal, (2) transport large amounts of water throughout vessels, (3) maintain high photosynthesis levels through a large leaf area to biomass ratio, (4) achieve rapid vertical and horizontal expansion by fast growth rates and various climbing mechanisms and (5) survive and recover from disturbances. Due to the competitive effects of vines on trees, management of vine growth is used to preserve tropical timber plantations, combat invasive weeds, and promote rainforest recovery. In order to sustainably manage the vines into the future, it is necessary to understand the mechanisms by which they can alter tropical forest succession and the impacts of various management techniques.     

Physiological studies on pea tendrils. XII. Effects of temperature on contact coiling and uncoiling

When excised tendrils of pea ( Pisum sativum L. cv. Alaska 2B) are mechanically perturbed and allowed to coil at different constant temperatures, the greatest amount of coiling occurs between 27°C and 33°C. Coiling of tendrils continues for about 2 h after mechanical perturbation at which time uncoiling usually begins. The temperature at which the rate of uncoiling is greatest appears to be influenced, at least in part, by the temperature at which the tendrils coiled. For example, when tendrils coil at 20°C their rate of uncoiling at 20°C is less than if they had coiled at 23°C. Estimated activation energies for the uncoiling process are greater than for coiling, with 35 J/mol × s and 97 J/mol × s for uncoiling in the temperature ranges 18°C to 23°C and 10°C to 18°C, respectively. The estimated activation energy for coiling is 5.4 J/mol × s. It is suggested that the process of tendril uncoiling, as well as tendril coiling, might be an active, energy requiring process.
When mechanically perturbed tendrils are placed in the cold (5°C) they do not coil. But this interruption of the coiling process with a cold (5°C) treatment, either immediately after mechanical perturbation or after coiling has begun, does not prevent coiling from continuing after tendrils are again given a more suitable temperature. It is concluded that the cessation of coiling during the cold period may be due to a slowdown in metabolism. It is suggested that there may be a factor which is responsible for the motor response and which is retained during the cold treatment.     

Diversity of Mechanical Architectures in Climbing Plants: An Evolutionary Perspective

Mechanical architectures of a wide range of climbing plants are reviewed from a wide phylogenetic range and evolutionary contingencies. They include an herbaceous lycopod (Lycopodiaceae) - a woody tropical liana (Apocynaceae), temperate climbers, herbs and shrubs (Ranunculacae), and two representative climbing palms (Arecoideae, Calamoideae). Trends in mechanical properties during development are reviewed and interpreted via changes in anatomical development of the stem and type of connection to host supports. The results indicate that there are some biomechanical features common to diverse climbing plants including (1) phases of relatively rigid stem growth where the climbing stem has to span between supports and (2) a mechanism to achieve greater compliancy towards the base or at points where the slender climbing stem is at risk from excessive mechanical stress. Evolutionary contingencies such as basal plesiomorphic constraint, complexification, simplification and developmental loss can drastically influence ways in which different plants have evolved different biomechanical climbing architectures. Two key developmental features controlling the biomechanics of the climbing stem are (1) the presence/absence of secondary growth and (2) the number, complexity and coordination of development of primary or secondary tissues with varying mechanical properties. Recent research has suggested that evolution of specialized climbing architectures can canalize subsequent evolution of alternative growth forms. The results suggest that the origin and type of climbing architecture can be heavily influenced by ancestral growth forms and architectures. Despite the extremely complex patterns of plant growth form evolution involving escapes to and from more specialized or simpler bauplans, selective pressure towards non-self-supporting growth forms is a remarkably persistent and iterative feature of growth form evolution in land plants.     

溪流粗木质残体的生态学研究进展

粗木质残体（CWD）是森林或溪流生态系统中残存的超过一定直径大小的站杆、倒木、枝桠及根系等死木质物的总称,溪流CWD对于溪流生态系统的稳定,水生生物多样性,河槽形态及其变化过程有着重要的作用。对溪流CWD的产生和分类,溪流CWD对于溪流生态系统的稳定,水生生物多样性,河槽形态及其变化过程有着重要的作用。对溪流CWD的产生和分类,溪流CWD贮量,分布和动态,以及溪流CWD的功能和管理分别进行了总结,并指出应尽快在国内开展溪流CWD的研究和管理。     

Allelopathy in Northern Temperate and Boreal Semi-Natural Woodland

Allelopathy has been widely investigated in forest ecosystems around the world. This ecological process takes part in the vegetation dynamics and partially explains the success or failure of seedling establishment and survival. Therefore, allelopathy could be a common cause of natural regeneration failure, due to adverse impact of understory species directly on trees species (inhibition of germination and seedlings primary growth). This problem has been investigated mainly in coniferous forests, but it also occurs in deciduous forests. Furthermore, allelopathy can involve forest soil microorganisms. They can act as allelochemical mediators, where they are able to inactivate these compounds by means of metabolization, as they are able to produce biologically active compounds using inactive molecules as a substrate. Special attention is given to mycorrhizal fungi and mycor-rhizae, because, in theory, they are able to protect seedlings against allelopathy. Applied aspects of allelopathy in forest ecosystems are also presented, with two main goals: (1) how to reduce the adverse impact of such interactions (chemical and mechanical control of allelochemicals plant producer, afforestation with selected mycorrhiza), but also (2) how to use allelopathy as a tool for forest management. Suggestions to improve the study of allelopathy in forest ecosystems and prospects for future investigations conclude this review.     

The need for a canopy perspective to understand the importance of phenotypic plasticity for promoting species coexistence and light-use complementarity in forest ecosystems

Because of their overwhelming size over other organisms, trees define the structural and energetic properties of forest ecosystems. From grasslands to forests, leaf area index, which determines the amount of light energy intercepted for photosynthesis, increases with increasing canopy height across the various terrestrial ecosystems of the world. In vertically well-developed forests, niche differentiation along the vertical gradient of light availability may promote species coexistence. In addition, spatial and temporal differentiation of photosynthetic traits among the coexisting tree species (functional diversity) may promote complementary use of light energy, resulting in higher biomass and productivity in multi-species forests. Trees have evolved retaining high phenotypic plasticity because the spatial/temporal distribution of resources in forest ecosystems is highly heterogeneous and trees modify their own environment as they increase nearly 1,000 times in size through ontogeny. High phenotypic plasticity may enable coexistence of tree species through divergence in resource-rich environments, as well as through convergence in resource-limited environments. We propose that the breadth of individual-level phenotypic plasticity, expressed at the metamer level (leaves and shoots), is an important factor that promotes species coexistence and resource-use complementarity in forest ecosystems. A cross-biome comparison of the link between plasticity of photosynthesis-related traits and stand productivity will provide a functional explanation for the relationship between species assemblages and productivity of forest ecosystems.     

Aspects of Gondwana paleobotany: gymnosperms of the Paleozoic—Mesozoic transition

During the late Paleozoic and early Mesozoic the Gondwana Supercontinent underwent dramatic geographic and climatic changes. Geologic and biologic factors concurrently played an important role modelling the vegetation of that time. The gymnospermic component of plant assemblages shows significant variations in composition and in the distribution of different taxa. Analysis of the assemblages shows that some plant groups dominated the scenario, such as the pteridosperms, glossopterids, corystosperms and, to a lesser degree, cordaites and conifers. Ginkgophytes, bennettites or cycads were less important in the Paleozoic but their numbers increased in the Triassic. Paleozoic assemblages were extensively dominated by glossopterids that became extinct in the earliest Mesozoic. Pteridosperms crossed the P—M barrier and became dominant during the Triassic, at a time when corystosperms evolved and radiated. Other groups became extinct in the Paleozoic, namely dicranophylls and cordaites. Conifers were represented by different families, restricted either to the Paleozoic or the Mesozoic. They were not conspicuous in the analysed assemblages. In some areas of Gondwana, taxa of the Euramerican alliance are present through a migrational mechanism that occurred during continental displacements which produced global climatic changes. Recent studies have shown that there are far more common elements between Euramerica and Gondwana than suspected up to now. These elements find their distribution especially in the western part of Gondwana (Africa—South America).