Rethinking plant community theory

Plant communities have traditionally been viewed as either a random collection of individuals or as organismal entities. For most ecologists however, neither perspective provides a modern comprehensive view of plant communities, but we have yet to formalize the view that we currently hold. Here, we assert that an explicit re-consideration of formal community theory must incorporate interactions that have recently been prominent in plant ecology, namely facilitation and indirect effects among competitors. These interactions do not suppport the traditional individualistic perspective. We believe that rejecting strict individualistic theory will allow ecologists to better explain variation occurring at different spatial scales, synthesize more general predictive theories of community dynamics, and develop models for community-level responses to global change. Here, we introduce the concept of the integrated community (IC) which proposes that natural plant communities range from highly individualistic to highly interdependent depending on synergism among: (i) stochastic processes, (ii) the abiotic tolerances of species, (iii) positive and negative interactions among plants, and (iv) indirect interactions within and between trophic levels. All of these processes are well accepted by plant ecologists, but no single theory has sought to integrate these different processes into our concept of communities.     

植物群落动态的模型分析

植物群落的动态是植物群落学的中心问题之一,包括更新、波动、演替、进化等主要内容。空间格局对种群和群落的动态起着至关重要的作用,种群空间格局和群落空间结构是群落中各种过程相互作用的产物。模型是描述群落动态、认识植物群落组建和维持机理的有效工具。本文阐述和比较了描述群落动态的四种具有代表性的经验模型,即镶嵌循环模型、随意游走模型、同资源种团比例模型、空间抢先占有模型及其机理。四种经验模型的空间性及缺陷分别是:(1)“镶嵌循环模型”考虑到了相邻斑块之间的植被空间结合在群落动态中的作用,而另外三种模型没有考虑到这一点;(2)在一定程度上,四种植物群落动态模型对各自针对的植物群落可能是适合的,但要作为描述群落动态发展的一般性模型还需要不断完善和发展;因为四种模型均没有考虑到自然干扰和人类干扰对植物群落动态的影响。作者对将来植物群落动态的研究及实践意义做出以下展望:(1)在不同空间尺度上,更加有效地评价控制群落动态变化的各种过程的相对重要性,并进一步将它们之间的复杂相互作用整合到群落动态模型中;(2)充分认识植物群落中存在的各种自然环境条件和生物群体的结构配置对植物群落动态发展的重要性;(3)重视植物群落动态发展中自然干扰过程和人类干扰过程的整合以     

Nonmanipulative determination of plant community dynamics

Knowledge of the strengths of interactions between species in plant communities is of fundamental importance to our understanding of how communities are structured, although they are notoriously difficult to quantify. Techniques have recently been developed that allow the detailed enumeration of the strength of interactions between plant species within unmanipulated multispecies communities. Nonlinear regression analysis is used to fit competition models to long-term census data using natural variations in plant densities in lieu of manipulation. The models generated have been used to infer the intensity and importance of interactions as well as to analyse the effects of spatial and temporal variability. Theoretical work has begun to look at how different techniques for measuring competition perform in a range of systems, highlighting the importance of spatial scale. The lessons learned from applying these methods will enable improved estimation of the strength of competition in natural communities.     

Long-term ant-species-dependent dynamics of a myrmecochorous plant community

Myrmecochory or seed dispersal by ants is a widely spread phenomenon, and myrmecochorous plants constitute a large portion of species in many ecosystems. Since the ant species complex in the ecosystem is continuously changing in time and space, the long-term effects of such ant–plant interactions on the plant community remained unclear. The manifold information obtained in numerous previous studies from one ecosystem in the deciduous forests of Central Ukraine allowed us to simulate the possible scenarios for plant survival and distribution in the ecosystem after a reduction in the number or local extinction of one of the ant species. The results of the virtual long-term experiment show that the abundance and spatial distribution of myrmecochorous plants strongly depends on both the abundance of ants and their species composition in the ecosystem. The positive role of ant species diversity for maintaining myrmecochorous plant species diversity is shown. Competition between plant species for seed dispersers is influenced by the ant community in such a way that the disappearance of one ant species may lead to the reduction or even local extinction of a particular plant population.     

大青沟森林植物群落物种多样性研究

大青沟森林植物种类非常丰富,约占内蒙古自治区植物种数的三分之一,生物资源十分丰富。本文分别用Simpson指数、Shannon-Wienner指数和均匀度指数计测生态优势度、不同植物群落的物种多样性、群落物种多度的均匀度。结果表明：由于大青沟森林植物群落属于隐域性植被,从沟底到沟沿,小气候的差异较为明显,存在着生境梯度,但由于乔、灌、草综合作用的影响,各群落类型及生境梯度上的物种多样性的差异不十分明显。这可能是特殊森林群落类型长期适应隐域性生境条件的结果,它为我们改造周边环境提供了有益的启示。     

植物群落功能多样性计算方法

以性状为基础的功能多样性指数在预测生态系统功能中起到越来越重要的作用.本文对近年来陆续出现的植物群落功能多样性指数进行综述.依据物种多样性指数的组成,功能多样性指数分为功能丰富度、功能均匀度和功能离散度指数.介绍了这3类指数的计算方法,有助于更好、更准确地理解“生物多样性-环境-生态系统功能”的关系.     

城市植物群落的减噪效果分析

在上海市区选取23个有代表性的城市植物群落进行减噪效益的测定。结果表明,植物群落对噪声的减弱效果和群落的结构组成有关。针叶树林和常绿阔叶树林的减噪效果最好,噪声衰减值均大于10dB;植物群落对噪声的减弱效果明显优于空旷地;建群种相同、林下层次多、植物种类丰富的群落对噪声的衰减效果优于林下无植被的群落;以落叶植物为优势种的群落在生长期对噪声的衰减值比落叶期高4～5dB。     

植物根际微生物群落构建的研究进展

植物根际是指植物根系与土壤的交界面,是根系自身生命活动和代谢对土壤影响最直接、最强烈的区域,其物理、化学和生物性质不同于土体土壤。在这个区域里,与植物发生相互作用的大量微生物,被称为根际微生物。根际微生物在植物的生长发育和植物病虫害的生物防治等方面都具有十分重要的意义。本文总结了根际微生物群落构建的研究现状,介绍了根际微生物的经典和最新的研究方法,包括根箱法、同位素技术以及高通量测序、菌群定量分析、高通量分离培养等方法在根际微生物研究中的应用,讨论了植物根系分泌物(碳水化物、氨基酸、黄酮类、酚类、激素及其信号物质)和土壤物理化学性质对根际微生物群落的影响,概述了根际微生物-植物的互作机制,以及根际微生物群落对植物的促生作用、提高植物抗逆性和抑制作用,并对根际微生物群落研究中存在的问题和未来发展方向进行了展望。     

Survivorship patterns in an annual plant community

Summary Age-specific survivorship was studied in a number of plant species which occur in a distinct, predominantly annual plant community of Texas, in association with the activities of pocket gophers. Of eleven species analyzed in detail, all functioned as annuals. Contrary to theoretical expectations, the species had low rates of juvenile mortality, and did not exhibit the demographic specializations of weedy or colonizing species. It is suggested that the annual habit in this case may be adaptive in sites with continual disturbance, such as that due to pocket gopher activity.     

Symbiotic bacteria as a determinant of plant community structure and plant productivity in dune grassland

Symbiotic interactions are thought to play a key role in ecosystems. Empirical evidence for the impact of symbiotic bacteria on plant communities is, however, extremely scarce because of experimental constraints. Here, in three complementary experiments, we show that nitrogen-fixing rhizobia bacteria act as a determinant of plant community structure and diversity. Grassland microcosms inoculated with a mixture of rhizobia had a higher above-ground plant productivity (+35%), contained more nitrogen (+85%) and had significant higher community evenness (+34%) than control microcosms without rhizobia. Moreover, three of the four studied legume species required rhizobia to successfully coexist with other plant species. In contrast, the growth and survival of three grass and five forb species were not affected by the presence or absence of rhizobia. Finally, our results also showed that the legume species largely relied on symbiotically fixed nitrogen, both in the field and in the microcosms. This indicates that results in the microcosms are indicative for processes occurring in the field. It is concluded that symbiotic interactions between plants and prokaryotes can contribute to plant productivity, plant community structure and acquisition of limiting resources in legume-rich grassland communities.     

Medium-term fertilization of grassland plant communities masks plant species-linked effects on soil microbial community structure

According to the singular hypothesis of plant diversity, different plant species are expected to make unique contributions to ecosystem functioning. Hence, individual species would support distinct microbial communities. It was hypothesized that microbial community dynamics in the respective rhizospheres of, two floristically divergent species, Agrostis capillaris and Prunella vulgaris that were dominant in a temperate, upland grassland in northern Greece, would support distinct microbial communities, in agreement to the singular hypothesis. Phospholipid lipid fatty acid (PLFA) profiles of the rhizosphere soil microbial community were obtained from the grassland which had been subjected to factorial nitrogen (N) and phosphorus (P) fertilization over five plant growth seasons. The soil cores analyzed were centered on stands of the two co-occurring target plant species, sampled from five blocks in all four factorial N and P fertilization combinations. Distinct PLFA clustering patterns following principle component analysis of PLFA concentrations revealed that, in the absence of P fertilization, soils under the two plant species supported divergent microbial communities. In the P fertilized plots, however, no such distinction could be observed. Results reveal that nutrient fertilization may mask the ability of plant species to shape their own rhizosphere microbial community.     

神头二电厂灰场植物群落分析研究

火电厂贮灰场常位于电厂附近平原地带,占地面积大,贮留时间长,以山西省神头二电厂马邑贮灰场为例,采用等级聚合分类分析。群落多样性与环境因子的方差分析和相关分析等方法。系统研究了灰场环境对植物群落类型,分布,多样性的影响。结果表明：灰场区植物分为4个群落,以强耐盐碱的碱蓬群落为优势群落,群落分布和多样性受灰场的影响较小,但随着土壤盐渍化程度的加重,植物群落多样性,均匀性呈下降趋势。     

Functional correlates of allelopathic potential in a successional plant community

Allelopathy, plant–plant interactions mediated through chemical production, is an active area of ecological research. Despite this widespread interest, we still lack community scale information on the prevalence of this interaction and the types of species that may be expected to be allelopathic. To address this research need, the allelopathic potential of 65 plant species from all stages of succession in the Piedmont region of New Jersey, USA, was determined with laboratory bioassays. The strength of each species’ allelopathic activity was then related to life form, origin, and fundamental plant traits. The vast majority of species tested exhibited significant allelopathic effects in the bioassays, with many of these having fairly strong effects. Overall, the allelopathic potential of species decreased with life span, roughly following the successional transitions from short-lived to long-lived herbs and to woody species. Herbaceous species on average were more allelopathic than woody species, but there was no difference between native and non-native species once life form was accounted for. In a principal components analysis, allelopathy was associated with other plant traits, but these relationships differed between woody and herbaceous species. Allelopathic potential was positively associated with plant height in herbaceous species, but negatively associated with height, leaf mass, and seed mass in woody species. These results indicate that allelopathy may be a quite common ecological strategy in plants and is equally common in both native and non-native species. The linkage of allelopathy with other plant functional traits suggests that allelopathy can and should be integrated into the broader suite of plant strategies that are studied.     

Jasmonate-mediated induced plant resistance affects a community of herbivores

1. The negative effect of induced plant resistance on the preference and performance of herbivores is a well‐documented ecological phenomenon that is thought to be important for both plants and herbivores. This study links the well‐developed mechanistic understanding of the biochemistry of induced plant resistance in the tomato system with an examination of how these mechanisms affect the community of herbivores in the field. 2. Several proteins that are induced in tomato foliage following herbivore damage have been linked causally to reductions in herbivore performance under laboratory conditions. Application of jasmonic acid, a natural elicitor of these defensive proteins, to tomato foliage stimulates induced responses to herbivory. 3. Jasmonic acid was sprayed on plants in three doses to generate plants with varying levels of induced responses, which were measured as increases in the activities of proteinase inhibitors and polyphenol oxidase. 4. Field experiments conducted over 3 years indicated that induction of these defensive proteins is associated with decreases in the abundance of all four naturally abundant herbivores, including insects in three feeding guilds, caterpillars, flea beetles, aphids, and thrips. Induced resistance killed early instars of noctuid caterpillars. Adult flea beetles strongly preferred control plants over induced plants, and this effect on host plant preference probably contributed to differences in the natural abundance of flea beetles. 5. The general nature of the effects observed in this study suggests that induced resistance will suppress many members of the herbivore community. By linking plant biochemistry, insect preference, performance, and abundance, tools can be developed to manipulate plant resistance sensibly and to predict its outcome under field conditions.     

Abundance-age-area relationships in an insular plant community

Two processes are thought to generate positive relationships between species richness and island area. The areaper se hypothesis states that larger islands maintain larger populations, which are less susceptible to extinction. The habitat hypothesis states that larger islands contain more habitats, and therefore a greater number of habitat specialists. However, the importance of each mechanism is debated. I tested the areaper se and habitat hypotheses by comparing relationships between plant abundance, age and island area in five shrub species on islands off the coast of British Columbia, Canada. Results showed that two shrub species increased in both abundance and age with island area. The remaining three species showed no differences in abundance and age with island area. Conifer abundances increased with island area, which generated differences in habitat availability. Smaller islands were dominated by open habitat, while larger islands contained both open and forested habitats. Changes in habitat availability with island area could explain patterns in plant abundance and age. The two species that increased in abundance with island area were commonly found in conifer forest on the mainland, and their distributions were consistent with the distribution forest habitat. Positive relationships between plant age and island area in these two species may result from lower survivorship in the open habitat, which dominated small islands. The three species that showed no relationship between abundance and island area are commonly found in open habitat on the mainland, and their island distributions paralleled the availability of open habitat on islands. Similar plant ages on different sized islands may result from their occurrence in open habitat on both large and small islands. Overall results support the habitat hypothesis and indicate that species distributions result from the interaction between habitat affinities and changes in habitat availability with island area.     

Litter controls plant community composition in a northern fen

The accumulation of litter or thatch can affect plant community composition by affecting the temperature, nutrient availability, and light availability of the soil environment, thereby forming a potentially important linkage between recent productivity and current ecosystem processes. To investigate the importance of litter on a fen peatland plant community, we conducted a litter addition and removal experiment in a fen in northern Minnesota, USA, between 1998 and 2001. The addition of litter had little effect on fen plant community composition or microenvironmental variables, despite a two-fold increase in litter mass compared to control plots. However, the removal of litter dramatically increased cover of Rhynchospora fusca and R. alba , and reduced cover of Carex exilis . Litter removal also increased availability of light and soil temperature and increased the phosphorus content of aboveground plant biomass. Our results indicate that litter is an important control of plant community composition in this northern fen.     

Arbuscular mycorrhizal fungi affect plant community structure under various nutrient conditions and stabilize the community productivity

Soil biota could have a significant impact on plant productivity and diversity through benefiting plants and mediating plant–plant interaction. However, it is poorly understood how soil biotic factors interaction with abiotic environments affect plant community diversity and composition. Here, we investigate the community‐level consequences of arbuscular mycorrhizal fungi (AMF) interactions with multiple nutrients and their ecological stoichiometry. We conducted a greenhouse experiment manipulating nitrogen (N) and phosphorus (P) to create soil nutrient availability and N:P gradients for microcosm communities with and without AMF. We found that AMF suppressed plant diversity at low P levels, whereas it did not alter the diversity at high P levels because of trade‐offs in the abundance of the dominant and subordinate species. AMF reduced plant diversity at the intermediate N:P ratios, while AMF did not affect the diversity at low and high N:P ratios. P addition decreased the mycorrhizal contribution to community productivity, whereas N addition reduced the negative effects of AMF on productivity at high P levels. AMF decreased community productivity at low N:P ratios but increased it at high N:P ratios. AMF increased the stoichiometric homoeostasis of plant communities, which was positively correlated with the stability of productivity under variations in soil N:P ratios. Our study demonstrates that both resource availability and stoichiometry influence the effect of AMF on plant community productivity and diversity and suggests that AMF may increase the stability of plant communities under variations in the soil nutrients by increasing the stoichiometric homoeostasis of the plant community.     

Seedling herbivory, community composition and plant life history traits

Despite the voluminous literature documenting plant-animal interactions, it is only recently that ecologists have begun to focus upon the importance of seedling herbivory in plant communities. This review aims to synthesize our current understanding of the effect that selective seedling removal by herbivores has in shaping post-disturbance plant community structure. In order to do this I describe how individual seedling and plant community characteristics influence the likelihood of seedling herbivory. I argue that seedling palatability, size and morphology, together with the frequency, distribution and timing of seedling emergence all play a significant role in determining seedling regeneration success in the face of herbivore attack. I also outline how current plant defence theories can be related to recent field observations concerning seedling acceptability and removal. In addition, I suggest that those seedling characteristics which provide the emerging plant with some degree of resistance against herbivory should be viewed as one component of a suite of plant life history traits affecting seedling regeneration success or failure. In view of the increasing importance of comparative methods in plant ecology, I propose that future research should integrate seedling acceptability with other plant life history traits thought to affect seedling regeneration. Recent work suggests that seed size may be paramount in determining regeneration success. I explore the possibility that seed size and seedling acceptability may be linked and discuss how these two factors may interact along successional gradients in plant communities.     

长白山阔叶红松林植物群落与昆虫群落的相互关系研究

通过季节性的观察,系统研究了长白山植物群落、昆虫群落多样性及它们之间关系。结果表明,植物群落物种丰富度指数与植食性昆虫丰富度指数呈负相关,而与捕食性天敌昆虫丰富度指数呈正相关,与寄生性天敌的丰富度指数呈负相关;昆虫群落的均匀度与植物群落的均匀度相关显著。植物群落的多样性指数与捕食性、寄生性天敌的多样性指数呈正相关。而与植食性昆虫的多样性指数呈负相关,这表明植物群落的多样性影响昆虫群落的多样性。     

Mycorrhiza influences plant community structure in succession on spoil banks

The experiment simulated a plant succession stage when perennial grasses (e.g. Calamagrostis epigejos) invade communities of annuals with different mycotrophy (e.g. Atriplex sagittata and Tripleurospermum inodorum) on coalmine spoil banks. Communities of these three model species were planted in 30 l microcosms either in the presence of pre-established mycelium network of three arbuscular mycorrhizal fungi (AMF) species (individually and in a mixture) or without AMF. Different AMF species had significantly different effects on individual plant species’ growth, which resulted in changes in plant community structure. While in the no-AMF treatment the non-mycotrophic plant species A. sagittata contributed nearly 70% to the total plant biomass, in the presence of the 3 AMF mixture the contribution of this species was only about 10%. Different effects of AMF on tiller formation by C. epigejos suggest that some AMF could have greater potential to promote the replacement of annuals by perennial grasses than others. It can be concluded that not merely the presence but also the identity of AMF present on spoil banks can affect the coexistence of plant dominants, the community structure and the progress of plant succession.