放牧对内蒙古锡林河流域草地群落植物茎叶生物量资源分配的影响

以内蒙古锡林河流域沿水分梯度分布的灰脉苔草(Carex appendiculata)、贝加尔针茅(Stipa baicalensis)、羊草(Leymus chinensis)、大针茅(Stipa grandis)、小叶锦鸡儿(Caragana microphylla)和冷蒿(Artemisia frigida) 6个草地群落为对象, 研究了围封禁牧与放牧样地中144个共有植物种的高度、丛幅面积、茎、叶和株(丛)生物量、茎叶比等性状。结果表明: 1)在个体水平上, 放牧样地中植物的生殖枝高度、营养枝高度、丛幅面积、单株(丛)生物量、茎、叶生物量和茎叶比均显著低于围封禁牧样地, 植物在放牧干扰下表现出明显的小型化现象; 2)在群落水平上, 放牧亦显著降低了群落总生物量和茎、叶生物量; 3)过度放牧显著改变了物种的资源分配策略, 使生物量向叶的分配比例增加, 向茎的分配比例减少。资源优先向同化器官分配可能是植物对长期放牧干扰的一种重要适应对策; 4)轻度放牧对物种的资源分配没有显著影响, 单株(丛)生物量和群落茎、叶及总生物量均表现出增加趋势, 这与过度放牧的影响正好相反。过度放牧引起的植物个体小型化改变了生态系统中物种的资源分配策略, 进而对生态系统功能产生重要的影响。     

Population distributions of plant size and light environment of giant ragweed (Ambrosia trifida L.) at three densities

Summary Plots in a naturally occurring population of giant ragweed (Ambrosia trifida L.) near Ames, Iowa, USA were left unthinned (high density,=693 plants/m²) or were thinned in early June 1989 to create low and medium densities of 10 and 50 plants/m². Size and light environment of individual plants were measured at monthly intervals from June to September. By September, low density plants had 15 times greater biomass/plant and 30 times greater leaf area/plant than high density plants, although biomass and leaf area per unit land area decreased with decreasing density. Plants at high density allocated more biomass to stem growth, but plants at medium and low density had successively higher leaf area ratios, higher potential photosynthetic rates, higher allocation to leaves, and higher growth rates. Average light on leaves decreased with increasing density and also decreased over the growing season in the low and medium densities. The distribution of light environments of individual plants was non-normal and skewed to the left in most months, in contrast to the rightwards skew of distributions of plant size parameters. Inequality in the distributions, as measured by coefficient of variation and Gini coefficients, increased over most of the growing season. There was little effect of density on inequality of stem diameter, height, or estimated dry weight, but inequality in reproductive output greatly increased with density. There was greater inequality in number of staminate flowers produced than in number of pistillate flowers and seeds produced. Path analysis indicated that early plant size was the most important predictor of final plant size and reproductive output; photosynthesis, conductance, and light environment were also significantly correlated with size and reproduction but usually were of minor importance. Variation in growth rate apparently increased inequality in plant size at low density, whereas belowground competition and death of smaller plants may have limited increases in inequality at high density.     

An ecophysiological approach to modelling resource fluxes in competing plants

A conceptual model of resource acquisition and allocation within a generalized, individual plant growing vegetatively in competition with others is presented. The model considers C and N acquisition, synthesis of assimilates and their transport and partitioning, growth of new tissues, reserve formation and recycling, and losses due to root exudation and respiration. These processes are regulated by the relative size of the C and N substrate pools in shoot and roots, in relation to meristematic sink strength. Translocation and allocation patterns are represented according to the Minchin phloem transport model. The current model is used to consider the impact of competition on resource acquisition and allocation, first by considering a plant growing in isolation and its response to manipulation of light, CO2 and N supplies. Secondly, competitive plants are introduced and the direct effects on plant responses in terms of resource depletion are considered separately from indirect effects such as potential changes in the quality of resources available (e.g. light quality or soil N sources). In the past, many studies of plant competition have not established the importance of these indirect effects because they have not established all the processes involved in competition. This model can be used to interpret responses of whole plants to their neighbours in terms of the relative importance of both the direct and indirect effects of competition.     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.     

The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

火柴头（Commelina benghalensis）实生植株资源配置及繁殖代价

火柴头具有地上和地下生殖枝开花结实的特性,产生地上大、小种子和地下大、小种子4种不同类型的种子.对4种类型种子实生植株的研究表明,4种类型种子实生植株个体水平上对新种群的贡献具有差异,地上大种子表现为最大,地下小种子则最小;4种类型种子实生植株在资源的繁殖配置上存在着差异,大种子尤其地上大种子对有性繁殖的资源分配最大,而地下小种子最小,这种差异又决定了在繁殖投资和繁殖代价上的差异,小种子特别是地下小种子实生植株的繁殖投资最小,而大种子特别是地上大种子实生植株的繁殖投资最大;从繁殖代价来看,大种子实生植株的繁殖代价之间差异不显著,而大种子实生植株的繁殖代价显著小于小种子实生植株的,地上小种子实生植株的繁殖代价显著小于地下小种子实生植株的.     

Representation of vegetation dynamics in the modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space

• 1 Advances in dynamic ecosystem modelling have made a number of different approaches to vegetation dynamics possible. Here we compare two models representing contrasting degrees of abstraction of the processes governing dynamics in real vegetation.
• 2 Model (a) (GUESS) simulates explicitly growth and competition among individual plants. Differences in crown structure (height, depth, area and LAI) influence relative light uptake by neighbours. Assimilated carbon is allocated individually by each plant to its leaf, fine root and sapwood tissues. Carbon allocation and turnover of sapwood to heartwood in turn govern height and diameter growth.
• 3 Model (b) (LPJ) incorporates a ‘dynamic global vegetation model’ (DGVM) architecture, simulating growth of populations of plant functional types (PFTs) over a grid cell, integrating individual‐level processes over the proportional area (foliar projective cover, FPC) occupied by each PFT. Individual plants are not simulated, but are replaced by explicit parameterizations of their growth and interactions.
• 4 The models are identical in their representation of core physiological and biogeochemical processes. Both also use the same set of PFTs, corresponding to the major woody plant groups in Europe, plus a grass type.
• 5 When applied at a range of locations, broadly spanning climatic variation within Europe, both models successfully predicted PFT composition and succession within modern natural vegetation. However, the individual‐based model performed better in areas where deciduous and evergreen types coincide, and in areas subject to pronounced seasonal water deficits, which would tend to favour grasses over drought‐intolerant trees.
• 6 Differences in model performance could be traced to their treatment of individual‐level processes, in particular light competition and stress‐induced mortality.
• 7 Our results suggest that an explicit individual‐based approach to vegetation dynamics may be an advantage in modelling of ecosystem structure and function at the resolution required for regional‐ to continental‐scale studies.

     

Biomass Allocation and Light Partitioning Among Dominant and Subordinate Individuals inXanthium canadenseStands

Patterns of above-ground biomass allocation and light captureby plants growing in dense stands or in isolation were studiedin relation to their height. A canopy model was developed tocalculate light absorption by individual plants. This modelwas combined with data on canopy structure and patterns of biomassallocation for solitary plants and for plants of different heightsin dense mono-specific stands of the dicotyledonous annualXanthiumcanadenseMill. There were four stands, and stand height increasedwith age and nutrient availability. The allometric relationshipbetween height and mass differed considerably between plantsin stands and those growing in isolation and also between plantsof different heights within stands. The proportion of shootmass in leaf laminae (LMR) decreased with increasing plant height,but solitary plants had a higher LMR than competing plants ofthe same height. Thus, in contrast to previous assumptions,LMR of competing plants is not strictly determined by biomechanicalconstraints but results from a plastic shift in biomass allocationin response to competition. Average leaf area per unit leafmass (SLA) decreased with increasing photosynthetic photon fluxdensity (PPFD) independent of nutrient availability. Consequently,taller, more dominant plants in stands had a lower leaf arearatio (LAR: LAR=LMRxSLA) than shorter, more subordinate plants.Dominant plants absorbed more light both per unit leaf area(     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.     

The Roles of Spatial Pattern and Size Variation in Shaping Height Inequality of Plant Population

Game-theoretic models predict that there is an ESS height for the plant population to which all individual plants should converge. To attain this conclusion, the neighborhood factors were assumed to be equal for all the individual plants, and the spatial pattern and size variation of population were left without consideration, which is clearly not right for the scenario of plant competition. We constructed a spatially-explicit, individual-based model to explore the impacts of spatial structure and size variation on individual plant’s height and population’s height hierarchies under the light competition. The monomorphic equilibrium of height that all the individual plants will converge to only exists for a population growing in a strictly uniform spatial pattern with no size variation. When the spatial pattern of the population is non-uniform or there’s size variation among individual plants, the critical heights that individual plants will finally reach are different from each other, and the height inequality at the end of population growth will increase when the population’s spatial pattern’s degree of deviation from uniform and population’s size variation increase. Our results argue strongly for the importance of spatial pattern and neighborhood effects in generating the diversity of population’s height growth pattern.     

The relationship between endophyte transition and plant species coexistence

The survival possibilities of terrestrial plant species are determined by their competitive abilities. One factor that affects competitive ability is the community of microorganisms that lives in association with the plants. Microorganisms affect the competitive dominance among plants by means of their metabolites. In this paper, we study the multiple plant species coexistence mediated by interactions with endophytes (fungi). The population dynamics are described by a revised lottery competition model for multiple plant species, each of which is divided into two classes: plants with endophytes (denoted EP) and plants without endophytes (NEP). The model includes the transition of seeds from EP to NEP. We show multiple species of plants cannot coexist in a steady state if this transition is density independent, but can coexist in a steady state if this transition is an increasing function of population density.     

The relationship between endophyte transition and plant species coexistence

The survival possibilities of terrestrial plant species are determined by their competitive abilities. One factor that affects competitive ability is the community of microorganisms that lives in association with the plants. Microorganisms affect the competitive dominance among plants by means of their metabolites. In this paper, we study the multiple plant species coexistence mediated by interactions with endophytes (fungi). The population dynamics are described by a revised lottery competition model for multiple plant species, each of which is divided into two classes: plants with endophytes (denoted EP) and plants without endophytes (NEP). The model includes the transition of seeds from EP to NEP. We show multiple species of plants cannot coexist in a steady state if this transition is density independent, but can coexist in a steady state if this transition is an increasing function of population density.     

Shade avoidance in the clonal herb Trifolium fragiferum/: a field study with experimentally manipulated vegetation height

In herbaceous canopies light availability can show high degrees of spatial variability in a vertical and also in a horizontal direction. Stoloniferous plants are hence likely to encounter differences in light availability during their ontogenetic development. Different mechanisms, such as petiole elongation, plasticity in internode length and branching, and an enhanced allocation to sexual reproduction have been suggested to represent viable shade-avoidance mechanisms for clonal plants.In a field experiment we tested the response of the stoloniferous herb Trifolium fragiferum L. to experimentally manipulated vegetation heights. Naturally occurring clonal fragments were exposed to four different vegetation heights ranging from 0 cm (high light availability created by clipping the surrounding natural vegetation at ground level) to 20 cm (natural shading in closed canopy). The growth and development of individual clones was followed for two months. At the end of the experiment above-ground plant parts were harvested. Growth-related and morphological parameters (e.g., petiole and internode length) as well as patterns of meristem utilization (i.e., flowering, branching) were recorded.Neither primary stolon growth and biomass accumulation nor branching and flowering were significantly affected by treatments. However, increased vegetation height resulted in a reduced number of secondary ramets and also had strong positive effects on petiole length, leading to marked changes in the architecture of plants growing in canopies of different heights. In addition, the average weight of individual ramets on the primary stolon was markedly higher in plants exposed to taller vegetation as compared to shorter vegetation.The results of this study suggest the occurrence of a trade-off between clonal expansion (i.e., secondary ramet production) and the average size of clonal offspring. If grown under higher vegetation plants invested more into the size of individual ramets, especially into elongating petioles, and less into the growth and development of lateral branches. Placing leaf laminae higher up in the canopy results in an enhanced light interception which has apparently buffered negative effects of increased vegetation height on whole-clone biomass. Plants grown under shorter vegetation invested more into lateral spread by producing more, but smaller ramets.     

Mammalian Herbivores Alter the Population Growth and Spatial Establishment of an Early-Establishing Grassland Species

Plant-herbivore interactions influence the establishment context of plant species, as herbivores alter the community context in which individual species establish, and the spatial relationship between individuals and their source population as plants invade. This relationship can be described using an establishment kernel, which takes into account movement through seed dispersal, and subsequent establishment of adults. Mammalian herbivores are hypothesized to influence plant population growth and establishment through a combination of consumption of seeds and seedlings, and movement of seeds. While the movement abilities of plants are well known, we have very few empirical mechanistic tests of how biotic factors like mammalian herbivores influence this spread potential. As herbivores of all sizes are abundant on the landscape, we asked the question, how do mammalian herbivores influence the population growth, spatial establishment, and the community establishment context of an early-recruiting native prairie legume, Chamaecrista fasciculata? We planted C. fasciculata in source populations within a four-acre tallgrass prairie restoration in plots with and without herbivores, and monitored its establishment with respect to distance from the source populations. We found that herbivores decreased population growth, and decreased the mean and range establishment distance. Additionally, C. fasciculata established more often without herbivores, and when surrounded by weedy, annual species. Our results provide insight into how the interactions between plants and herbivores can alter the spatial dynamics of developing plant communities, which is vital for colonization and range spread with fragmentation and climate change. Mammalian herbivores have the potential to both slow rates of establishment, but also determine the types of plant communities that surround invading species. Therefore, it is essential to consider the herbivore community when attempting to restore functioning plant communities.     

Trade-offs between flowering time,plant height,and seed size within and across 11 communities of a QingHai-Tibetan flora

Flowering timing is of fundamental biological importance for its tight association with pre-flower growth states and subsequent reproduction success. Here, we selected plant height and seed size to represent plant growth and reproduction states, respectively, and analyzed their associations with flowering time in 11 communities together representing a QingHai-Tibetan flora. Trait associations were examined using Pearson correlation analyses (TIPs) and phylogenetically independent contrasts (PICs) within individual communities and meta-analyses across all communities. The results of TIPs-based and PICs-based analyses were generally congruent, although fewer contrasts were significant with PICs, probably because of low statistical power. Overall, flowering time was negatively correlated with seed size and plant height (i.e., plants with larger seeds and stature started flowering earlier) in various woody communities, but correlations were neutral or positive in herbaceous communities. The seed size–flowering time relationship was negative for woody and herbaceous perennials but not for annual herbs in most communities. The relationship between plant height and flowering time was negative for woody but positive for herbaceous plants. Moreover, the lack of difference in time–size relationships between anemophilous and entomophilous plants suggests that pollination type may only be a secondary force in controlling flowering phenology. Our studies demonstrate that environmental conditions, community structure, and plant life history strategies may affect community flowering time singly or in combination.     

Costs versus risks: Architectural changes with changing light quantity and quality in saplings of temperate rainforest trees of different shade tolerance

Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome‐mediated stem elongation in response to changes in red : far red ratio, while shade‐tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old‐growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade‐tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.     

Plants in a crowded stand regulate their height growth so as to maintain similar heights to neighbours even when they have potential advantages in height growth

Background and Aims

Although being tall is advantageous in light competition, plant height growth is often similar among dominant plants in crowded stands (height convergence). Previous theoretical studies have suggested that plants should not overtop neighbours because greater allocation to supporting tissues is necessary in taller plants, which in turn lowers leaf mass fraction and thus carbon gain. However, this model assumes that a competitor has the same potential of height growth as their neighbours, which does not necessarily account for the fact that height convergence occurs even among individuals with various biomass.

Methods

Stands of individually potted plants of Chenopodium album were established, where target plants were lifted to overtop neighbours or lowered to be overtopped. Lifted plants were expected to keep overtopping because they intercept more light without increased allocation to stems, or to regulate their height to similar levels of neighbours, saving biomass allocation to the supporting organ. Lowered plants were expected to be suppressed due to the low light availability or to increase height growth so as to have similar height to the neighbours.

Key Results

Lifted plants reduced height growth in spite of the fact that they received higher irradiance than others. Lowered plants, on the other hand, increased the rate of stem elongation despite the reduced irradiance. Consequently, lifted and lowered plants converged to the same height. In contrast to the expectation, lifted plants did not increase allocation to leaf mass despite the decreased stem length. Rather, they allocated more biomass to roots, which might contribute to improvement of mechanical stability or water status. It is suggested that decreased leaf mass fraction is not the sole cost of overtopping neighbours. Wind blowing, which may enhance transpiration and drag force, might constrain growth of overtopping plants.

Conclusions

The results show that plants in crowded stands regulate their height growth to maintain similar height to neighbours even when they have potential advantages in height growth. This might contribute to avoidance of stresses caused by wind blowing.     

Basal rosette or floating leaf canopy – an example of plasticity in a rare aquatic macrophyte

The rare aquatic macrophyte Luronium natans can be encountered with two growth forms: as a bottom-dwelling plant with a rosette of linear leaves, or as a nymphaeid plant with long-petioled oval floating leaves. The change of growth form corresponds to a change in size class (small and submerged vs. tall and canopy-forming). The present study compares through one growing season floating leaf production and patterns of biomass allocation in Luronium ramets from a natural, moderately nutrient-rich habitat and from nutrient-rich transplantation sites. We ask whether differences in gross floating leaf production result from differences in ramet vigour while allocation patterns remain stable, or whether Luronium is able to allocate biomass plastically, and thus to change its growth form with differences in habitat. The study shows that both leaf types were produced in all habitats since the mid-growing season (June), but that biomass allocation to them varied. Floating leaves were dominant at high nutrient levels, whereas at the moderate nutrient level most leaf biomass was found in the rosette. We suggest that Luronium modifies its biomass allocation in a pattern that corresponds to the outlines of Tilman's (1988) mechanistic model of optimal biomass allocation on a light:nutrient gradient. The demonstrated morphological plasticity may enable Luronium to maintain itself in a large range of habitats, but it raises new questions about the reasons for the species' rarity.     

Integration and scaling of UV-B radiation effects on plants: the relative sensitivity of growth forms and interspecies interactions

Aims The relative plant type sensitivity and selected community interactions under increased UV-B radiation where examined. Specifically, we investigated: (i) if there are differences among growth forms in regard to their sensitivity to UV-B radiation, (ii) if increased UV-B radiation influences the plant competitive balance in plant communities and (iii) the response mechanisms of the UV-B radiation-sensitive species that might increase their fitness.Methods To answer our research questions, we used a mechanistic model that, for the first time, integrated the effects of increased UV-B radiation from molecular level processes, whole plant growth and development, and community interactions.Important findings In the model simulations, species types exhibited different levels of sensitivity to increased UV-B radiation. Summer C₃ and C₄ annuals showed similar growth inhibition rates, while biennials and winter C₃ annuals were the most sensitive. Perennials exhibited inhibitions in growth only if increased UV-B radiation results in increases in metabolic rates. In communities, species sensitive to UV-B radiation may have a competitive disadvantage compared to resistant plant species. But, sensitive species may have a wide array of responses that can increase their fitness and reproductive success in the community, such as, increased secondary metabolites production, changes in timing of emergence and reproduction, and changes in seed size. While individual plants may exhibit significant inhibitions in growth and development, in communities, these inhibitions can be mitigated by small morphological and physiological adaptations. Infrequent or occasional increased UV-B radiation events should not have any lasting effect on the structure of the community, unless other environmental factors are perturbing the dynamic equilibrium.     

植物种群更新限制——从种子生产到幼树建成

更新限制是指种子由于各种原因,不能够萌发并生长成幼树。它作为解释生物多样性的理论,一直受到国内外群落生态学家关注。从种源限制、传播限制和建成限制3个角度,对更新限制机制研究进展进行了综述。从种源限制而言,时空因素是影响植物种群更新限制的重要因素,因为植物结实量存在明显时空变化,造成植物更新个体出现明显的时空规律。从传播限制而言,传播数量、距离和食果动物行为均限制植物种群更新。数量上,缺乏有限传播者势必减少传播数量,但如果种子拥有较高质量,则能逃脱数量限制;距离上,植物更新个体显示出明显的Janzen-Connell格局,但传播距离趋向稳定,形成植物种群的进化稳定对策;食果动物行为上,不同传播者对更新贡献存在差异,捕食者直接降低更新,融入两类动物行为的模型更能反映食果动物对更新的限制。从建成限制而言,环境因子制约植物生长。小尺度下,微生境的好坏对于植物幼苗建成至关重要;大尺度下,植物提供较好的广告效应则能摆脱生境限制。将传播者行为、捕食者行为与幼苗的空间分布格局、种子传播机理模型等结合,建立植物更新限制机理模型应是更新限制未来的研究热点。选择稀有种和古老种为主题的长期更新限制研究,为种群恢复提供指导,也是未来重要研究方向。