Assessing diversity in plant communities: The importance of within-species variation

While the measurement of plant species diversity continues to play a central role in ecology and conservation, few formal attempts have been made at defining the concept of diversity, and, specifically, at evaluating the utility of taxonomic species as units for diversity indices. Ecological diversity is defined here as a measure of the degree of biotic and/or abiotic dissimilitude within a community that is perceivable and utilizable by organisms. Although indices based merely on ‘species’ may be useful for cataloging taxonomic diversity in communities, plant taxa are generally unreliable units for quantifying the ecological diversity perceived and utilized by most organisms in communities. Recent research highlights the shortcomings of the unit of species for characterizing ecological diversity, and we advocate the further exploration of alternative diversity classes with which to describe plant communities.     

我国洛阳与菏泽牡丹主栽园区AM真菌多样性研究

为探明我国特有花卉牡丹 (Paeonia suffruticosa) 根围内的丛枝菌根(AM)真菌资源状况, 作者对河南省洛阳市与山东省菏泽市牡丹主产区土壤中的AM真菌进行了调查。共分离到AM真菌5属35 种, 其中球囊霉属(Glomus)在各采样点相对多度最高, 其次是无梗囊霉属(Acaulospora)。两地土壤中AM真菌种的丰度、孢子密度和物种多样性指数等存在差异: 菏泽赵楼牡丹园AM真菌种的孢子密度最高,而其种的丰度最低; 洛阳矬里牡丹种苗基地的孢子密度最低; 菏泽种苗基地的Shannon-Wiener指数显著高于其他样地。地球囊霉(Glomus geosporum)是洛阳王城公园和菏泽赵楼牡丹园的优势种; 缩球囊霉(Glomus constrictum)为洛阳土桥花木基地、洛阳牡丹园、菏泽牡丹种苗基地和菏泽赵楼牡丹园的优势种。本研究结果表明我国牡丹主栽园区AM真菌具有丰富的多样性。     

Revealing hidden plant diversity in arid environments

Estimating total plant diversity in extreme or hyperarid environments can be challenging, as adaptations to pronounced climate variability include evading prolonged stress periods through seeds or specialized underground organs. Short‐term surveys of these ecosystems are thus likely poor estimators of actual diversity. Here we develop a multimethod strategy to obtain a more complete understanding of plant diversity from a community in the Atacama Desert. We explicitly test environmental DNA‐based techniques (eDNA) to see if they can reveal the observed and ‘hidden' (dormant or locally rare) species. To estimate total plant diversity, we performed long‐term traditional surveys during eight consecutive years, including El Niño and La Niña events, we then analyzed eDNA from soil samples using high‐throughput sequencing. We further used soil pollen analysis and soil seed bank germination assays to identify ‘hidden' species. Each approach offers different subsets of current biodiversity at different taxonomic, spatial and temporal resolution, with a total of 92 taxa identified along the transect. Traditional field surveys identified 77 plant species over eight consecutive years. Observed community composition greatly varies interannually, with only 22 species seen every year. eDNA analysis revealed 37 taxa, eight of which were ‘hidden' in our field surveys. Soil samples contain a viable seed bank of 21 taxa. Soil pollen (27 taxa) and eDNA analysis show affinities with vegetation at the landscape scale but a weak relationship to local plot diversity. Multimethod approaches (including eDNA) in deserts are valuable tools that add to a comprehensive assessment of biodiversity in such extreme environments, where using a single method or observations over a few years is insufficient. Our results can also explain the resilience of Atacama plant communities as ‘hidden' taxa may have been active in the recent past or could even emerge in the future as accelerated global environmental change continues unabated.     

The emergence of diversity in plant communities

The diversity of functional forms and strategies in plant communities is essential to the maintenance of the services that ecosystems provide humanity, and ultimately to the homeostasis of the biosphere. This diversity emerges from evolutionary forces operating at lower levels; these exploit the opportunities for specialization presented by exogenous and endogenous spatial and temporal heterogeneity. Two major theoretical approaches have been taken to understand how strategies arise and are maintained: optimization models, which consider the fitnesses of types in isolation, and game-theoretic methods, which take frequency dependence into account. The game-theoretic approach is more powerful, but also more challenging to apply. For some relatively simple problems in the study of biodiversity, we show how the game-theoretic formulation can be translated into an equivalent problem in optimization. More generally, however, new techniques will be needed to explore the dynamics of multiple coexisting types and strategies.     

接种丛枝菌根（AM）真菌对植物DBP污染的影响

在温室进行盆栽试验,以DBP(邻苯二甲酸二丁酯)为研究对象,以豇豆(Pigna sinensis)为宿主植物,分别接种AM真菌Acaulospora lavis(光壁无梗球囊霉)和Glomus caledonium(苏格兰球囊霉),观察接种AM真菌对植物DBP污染变化的影响．结果表明,接种AM真菌明显控制了植物对DBP的吸收,降低了植物体内DBP的浓度．在低浓度DBP(4mg.kg^-1)土壤处理时,接种Acaulospora lavis和Glomus caledo-nium分别使植物体内DBP浓度比不接种(CK)最大下降32．7％和21．7％;高浓度DBP(100mg.kg^-1)土壤处理时,分别比CK最大下降30．5％和30．0％．接种AM真菌还抑制了DBP由植物根系向地上部的迁移,对减轻植物遭受DBP污染起了一定的作用．     

陆地植物群落物种多样性研究进展

生物多样性是当前生态学研究的热点之一,物种多样性层次是最直接、最易观察和最适合研究生物多样性的层次。总结了与群落动态、生境因子、取样尺度及生态系统相关的陆地植物物种多样性研究。同时,根据目前的趋势提出了多样性动态研究的发展动向。     

Assessing the impact of land abandonment, nitrogen enrichment and fairy-ring fungi on plant diversity of Mediterranean grasslands

Semi-natural calcareous grasslands are of great conservation interest because of their high species richness, but they are threatened by land abandonment and nitrogen eutrophication. These plant communities evolved as a result of a long history of human activity, which generated and maintained these habitats by extensive grazing and mowing. Calcareous grasslands are listed as a priority for conservation in the EC Habitats Directive. However, the effects of different management regimes, nitrogen enrichment, and soil-borne pathogens on plant species diversity are less clear for grasslands of the Mediterranean Basin, compared to meadows in Northern and Central Europe. In this study, we assessed the impact of land abandonment, nitrogen enrichment, and fairy-ring fungi on species diversity in semi-natural grasslands found in the Mediterranean Basin by comparing the available literature with findings from recent studies carried out in Central Italy. In a series of field experiments, the cutting of abandoned grassland consistently reduced the living biomass of the dominant perennial grasses, such as Brachypodium rupestre and Bromus erectus, and promoted a rapid increase in species richness and diversity by allowing the establishment of rare species. There was a similar, but less effective, restoration of species diversity and composition in mowed grassland after litter removal. We also show that nitrogen enrichment at levels comparable to atmospheric deposition depresses species diversity, which also hampers the positive effects of litter removal. Our findings are consistent with previous results achieved in Northern and Central Europe, which however, mainly focused on grasslands with intermediate to high primary productivity levels. The limited availability of data from low-productivity, drought-prone Mediterranean grasslands requires further studies to assess the impact of land abandonment and nitrogen eutrophication in such ecosystems. Finally, we discuss the role of fairy-ring fungi in the maintenance of plant diversity in species-rich grassland. We show that fairy-ring fungi (e.g. Agaricus campestris) critically affect the spatial distribution and diversity of coexisting plant species. By killing the dominant perennial herbs, these radially growing plant pathogens produce empty niches for rare, short-lived species, thus affecting the vegetation pattern. Overall, our results are of interest for environmental managers, as they provide guidelines for the restoration of abandoned areas and the conservation of these species-rich habitats.     

Hidden diversity of endophytic fungi in an invasive plant

Fungal endophytes are important in plant ecology and common in plants. We attempted to test cointroduction and host-jumping hypotheses on a community basis by comparing endophytes isolated from invasive spotted knapweed (Centaurea stoebe, Asteraceae) in its native and invaded ranges. Of 92 combined, sequence-based haplotypes representing eight classes of Fungi, 78 occurred in only one of the two ranges. In the native range of C. stoebe, one haplotype of Alternaria alternata was clearly dominant, whereas in the invaded range, no haplotype was dominant. Many haplotypes were closely related to one another and novel. For example, six putative, new species of Botrytis were discovered as endophytes of C. stoebe, which has never been reported to have Botrytis spp.. Apparent differences between the two communities of endophytes were significant according to an analysis of similarity, but phylogenetic community structure did not differ significantly between the ranges. Both host-jumping and cointroduction of fungal endophytes likely took place during the spotted knapweed invasion.     

Facilitation can increase the phylogenetic diversity of plant communities

With the advent of molecular phylogenies the assessment of community assembly processes has become a central topic in community ecology. These processes have focused almost exclusively on habitat filtering and competitive exclusion. Recent evidence, however, indicates that facilitation has been important in preserving biodiversity over evolutionary time, with recent lineages conserving the regeneration niches of older, distant lineages. Here we test whether, if facilitation among distant-related species has preserved the regeneration niche of plant lineages, this has increased the phylogenetic diversity of communities. By analyzing a large worldwide database of species, we showed that the regeneration niches were strongly conserved across evolutionary history. Likewise, a phylogenetic supertree of all species of three communities driven by facilitation showed that nurse species facilitated distantly related species and increased phylogenetic diversity.     

Distribution of arbuscular mycorrhizal fungi in four semi-mangrove plant communities

To better understand the diversity and species composition of arbuscular mycorrhizal fungi (AMF) in mangrove ecosystems, the AMF colonization and distribution in four semi-mangrove plant communities were investigated. Typical AMF hyphal, vesicle and arbuscular structures were commonly observed in all the root samples, indicating that AMF are important components on the landward fringe of mangrove habitats. AMF spores were extracted from the rhizospheric soils, and an SSU rDNA fragment from each spore morph-type was amplified and sequenced for species identification. AMF species composition and diversity in the roots of each semi-mangrove species were also analyzed based on an SSU-ITS-LSU fragment, which was amplified, cloned and sequenced from root samples. In total, 11 unique AMF sequences were obtained from spores and 172 from roots. Phylogenetic analyses indicated that the sequences from the soil and roots were grouped into 5 and 14 phylotypes, respectively. AMF from six genera including Acaulospora, Claroideoglomus, Diversispora, Funneliformis, Paraglomus, and Rhizophagus were identified, with a further six phylotypes from the Glomeraceae family that could not be identified to the genus level. The AMF genus composition in the investigated semi-mangrove communities was very similar to that in the intertidal zone of this mangrove ecosystem and other investigated mangrove ecosystems, implying possible fungal adaptation to mangrove conditions.     

百山祖自然保护区植物群落beta多样性

本文采用植物群落学的典型样方法,研究了百山祖自然保护区森林植物群落beta多样性格局及其维持机制。通过对45个20m?20m标准样地的调查数据进行分析,运用Chao’s群落距离指数衡量该植物群落beta多样性格局,并通过Mantel检验、基于距离矩阵的偏RDA分析和方差分解等方法初步检验和衡量了各环境因子差异（包括群落郁闭度、海拔、坡度、坡向和坡位）和群落空间距离对该区域beta多样性格局的影响。结果显示,该区域内植物群落beta多样性随着群落间综合环境差异或群落空间距离的增加而增大, 但环境差异和群落空间距离只能解释36%左右的beta多样性格局。检验的5个环境因子中,只有群落郁闭度和海拔对百山祖自然保护区植物群落beta多样性有显著影响,并且群落郁闭度对beta多样性的解释度（20.0%）略高于海拔对beta多样性的解释度（18.0%）。群落空间距离对百山祖自然保护区beta多样性的解释度最小（9.0%）。本文展现了百山祖自然保护区内植物群落beta多样性格局及其与群落环境和空间距离的关系,所获得的结果支持生境异质性和扩散限制联合对植物群落beta多样性起作用的假说。     

Development of species diversity in some mediterranean plant communities

Summary Plant communities in the Mediterranean region have been analyzed with the emphasis on community processes regulating diversity trends. We want to know how several mechanisms that contribute to the maintenance or to the modification of species diversity, act: (i) in different communities, during an ecological succession (from old fields to forests), and (ii) in forest communities throughout the year. Some of these mechanisms were investigated through difference in stratification, life-form, phenology, dispersal agent, and microenvironmental gradient.The paper censists of two parts. The first one deals with the relationship between structural and biological diversity in conjunction with succession stages leading to a Quereus pubescens forest. It is concluded that diversity, however it is measured, fluctuates during the succession: it increases initially (15 years after abandonment) and also in later stages when trees appear in the fields; it decreases after 20 years when Brachypodium phoenicoides dominates and in the latest stages of the succession studied. These trends may be interpreted in relation to the evolution of life form and dispersal agents spectra during the succession.The second part concerns community-structure and biological diversity in relation to the organization of two Quercus pubescens forests. It appears that the species richness in the understory of the forests, may be explained by: (i) the tendency of the modal height of species foliage distribution to oceupy different positions, (ii) the quasicomplete asynchronism in the major phenophases of the dominant species, (iii) different horizontal patterns of species distribution along a light gradient.These schemes are discussed in relation to ecological hypotheses on diversity in relation to succession, and to community organization.Nomenelature follows: P. Fournier (1961). Les quatre flores de France for the Gramineae and Liliaceae, Flora Europea for the other taxa.The support of the Délégation de la Recherche Scientifique et Technique through the grants N567, N633, N674 (Structure et dynamique des formations à Chène pubescent en zone bioclimatique méditerranéenne) is acknowledged. We thank J. Biondel, R. Bonhomme and M. Dueray for technical and scientific assistance. We are greatly indebted to Dr. E. van der Maarel for his helpful improvements of this text.     

厦门市七种药用植物根围AM真菌的侵染率和多样性

调查了福建省厦门市7种常见药用植物根围丛枝菌根真菌分布情况、侵染率及其多样性。结果表明:7种药用植物均能与AM真菌形成良好的共生关系,且不同药用植物形成菌根的能力差异明显,盐肤木根围的孢子密度最高,29.0个/g土,喜树的侵染率最高,100%。含笑根围的孢子密度最低,4.7个/g土,鱼腥草的总侵染率最低,4.5%。共分离鉴定AM真菌4属63种,其中球囊霉属(Glomus)39种、无梗囊霉属(Acaulospora)18种、巨孢囊霉属(Gigaspora)4种、盾巨孢囊霉属(Scutellospora)2种,其中Glomus、Acaulospora为优势属,黑球囊霉G.melanosporum为优势种。盐肤木根围AM真菌种类最丰富,Shannon-Weiner指数H达到1.29。侵染率与各土壤因子均无显著相关;孢子密度与pH值极显著负相关;种的丰度与pH值显著负相关、与电导率极显著负相关、与孢子密度极显著正相关;Shannon-Weiner指数H与有机质极显著负相关;均匀度与有机质、孢子密度极显著负相关。厦门地区AM真菌资源十分丰富,多样性程度高,宿主植物不同,土壤因子对其侵染率、孢子密度、种的丰度、Shannon-Weiner指数、均匀度的影响也不同。为实现AM真菌生物技术应用于中药材规范化种植提供宝贵种质资源和理论依据。     

干旱、半干旱区湖泊周围盐生植物群落的多样性格局及特点

干旱、半干旱地区湖泊周围是盐渍化土壤的主要分布区,盐渍化是荒漠化的主要类型之一。目前,关于盐生植被的分布格局及群落多样性随着盐渍化程度加深的动态变化的研究仍很缺乏, 为阐释这种关系,作者在内蒙古干旱、半干旱地区选择吉兰泰(盐池)、乌梁素海、查干诺尔(碱矿)以及额吉诺尔(盐池)等4个湖泊,研究了其周围盐生植物群落的物种组成、分布特征以及群落结构的差异, 讨论了群落多样性沿盐分梯度的变化特点, 并在此基础上探讨了盐生植物群落对土壤盐分环境的指示意义。为建立群落耐盐值与群落多样性的关系,我们计算了群落耐盐值。结果表明, 盐生植物群落沿盐湖呈明显的环带状分布;随着土壤盐渍化程度的增加, 按照芨芨草群落(Comm. Achnatherum splendens)、盐爪爪群落(Comm. Kalidium foliatum)、盐角草群落(Comm. Salicornia europaea)和碱蓬群落(Comm. Suaeda glauca)的顺序演替, 而且物种种类趋向单一化, 群落结构趋向简单化。群落的物种多样性和群落间物种的替代速率都随土壤盐分的增加而减小, 而群落间物种的相似性则增加。区域性气候特点对盐生植物群落的特征也会产生一定的影响, 特别是在低盐渍化的条件下, 这种影响比较显著, 使得盐生植物群落体现出地带性的特点, 而随着土壤盐渍化程度的提高, 盐生植物群落的隐域性特征更为突出。因此, 这一地区的盐生植被又呈现出非常明显的地带性植被向非地带性植被过渡的特点。     

Efficient sampling of plant diversity in arid deserts using non-parametric estimators

Surveying plant diversity in arid desert areas is extremely difficult because of the harsh climate, hostile terrain, lack of roads, and insecurity, which is why it is particularly important to improve the sampling efficiency, but few relevant studies have been done. The performance of non-parametric estimators was assessed with first-hand field data to determine (a) the threshold of the proportion of uniques (number of species that occur in exactly one plot divided by the number of species sampled) that involves the least sampling effort and (b) the method of locating plots to obtain a more reliable estimate of species richness. The study area (Gurbantunggut desert, China) was divided into five sub-regions based on variation in physical environment and vegetation. The following common correction factors were selected: ACE, Chao1, Bootstrap, Chao2, ICE, Jack1, and Jack2. The estimates for each sub-region (partition) and for the entire region (without partition), the threshold of proportion of uniques, and the method of determining sampling locations (including prior sampling of plots that show large differences in habitats) were compared in terms of their ability to predict the number of species more accurately. We found that ACE and Chao1 (which use abundance data) showed more biased estimates than the other factors (incidence data), and best estimator is Jack1. Species richness was significantly underestimated for the region, but the non-parametric estimators could estimate the species richness for each sub-region reliably. Sampling locations affected the performance of non-parametric estimators significantly. The threshold of minimum sampling was 15% and that of uniques was 30%; the two were able to limit the bias within 5 and 10%, respectively. It is concluded that the non-parametric estimators can estimate the plant diversity of arid deserts reliably from the data on incidence. The study area (on the scale of a region) should be partitioned to improve the performance of the non-parametric estimators. The plots with larger differences in habitats should be sampled more extensively based on the threshold of the proportion of uniques.     

Aggregated seed arrival alters plant diversity in grassland communities

Aims Species aggregation is commonly seen in plant communities and may increase diversity by causing intraspecific competition to exceed interspecific competition. One potential source of this spatial aggregation is seed dispersal but it is unclear to what extent aggregated seed distributions affect plant diversity in real communities. Using a field experiment, I tested whether uniform or aggregated seed arrival alters community structure and whether these effects vary with sowing density.Methods The experiment consisted of two spatial seeding treatments (uniform and aggregated) that were fully crossed with three seed density treatments. Sixty, 3 × 4-m plots were arrayed in a low-diversity grassland located in Kansas, USA. Each plot was divided into forty-eight, 0.5 × 0.5-m patches. For aggregated seeding treatments, each of the 15 species was sown into three randomly selected patches within the plot (3×15 = 45). To create a uniform species arrival but control for the seed addition method, all 15 species were sown into 45 individual patches (with three patches remaining unsown) within each plot. Seed mass for each species was held constant at the plot scale between uniform or aggregated treatments within a given level of the sowing density treatment. After two growing seasons, plant density was quantified for all sown species in 15 randomly selected patches from each plot.Important findings I found evidence for shifts in community structure in response to the different spatial seeding patterns. The evenness of added species was higher under aggregated than uniform sowing patterns. There was no detectable effect of aggregated seed sowing on species richness at 3.75 m 2 scale. However, when species richness was extrapolated to larger scales (11.25 m 2), aggregated sowing was predicted to have greater richness than uniform sowing. Effects of seed aggregation on community structure were apparent only at moderate to high sowing rates, yet the latter are within the range of measured seed dispersal in similar grasslands. Additionally, as sowing density increased, seed mass became an increasingly effective predictor of relative abundances for added species, but only under uniform sowing patterns supporting the idea that aggregated dispersal may buffer weaker (smaller seeded) species from competition during colonization. This is the first experiment to show that aggregated seed dispersal patterns can increase at least some components of plant diversity in undisturbed grasslands and suggests that previous seed dispersal experiments, which utilize uniform seed sowing, may underestimate the potential effect of dispersal on plant community structure.     

Conserving plant genetic diversity for dependent animal communities

While population genetic diversity has broad application in species conservation, no studies have examined the community‐level consequences of this diversity. We show that population genetic diversity (generated by interspecific hybridization) in a dominant riparian tree affects an arthropod community composed of 207 species. In an experimental garden, plant cross type structured the arthropod community of individual trees, and among stands in the wild, plant genetic diversity accounted for nearly 60% of the variation in arthropod diversity. While previous experimental garden studies have demonstrated the effects of plant genotype on arthropod communities, our study extends these findings from individual trees in an experimental garden to natural stands of cottonwoods where plant population genetic diversity was a significant factor structuring arthropod diversity. These findings argue that the preservation of genetic diversity in a dominant species is far more important than previously realized, and may be particularly important in hybridizing systems.     

三江平原湿地典型植物群落物种多样性研究

以三江平原分布最广的毛果苔草(Carex lasiocarpa)群落和小叶章(Calamagrostis angustifolia)群落为研究对象,研究2个群落的植物物种及其组成特征。结果表明,毛果苔草群落以毛果苔草为优势种,以漂筏苔草(C.pseudocuraica)为亚优势种,二者的重要值之和为56.4%;小叶章群落以小叶章为优势种,其重要值为50.8%。物种多样性分析表明,毛果苔草群落和小叶章群落的Simpson指数(D)、Shannon-Wiener指数(H)和Pielou均匀度指数(J)均有较大波动,且H与J呈显著正相关,与D呈显著负相关,与S无显著相关关系;毛果苔草群落的H、D、J和S均高于小叶章群落,但差异不显著;2群落的相似性指数为46.5%,表明二者间存在一定的联系。     

佛坪国家级自然保护区植物群落物种多样性特征

用物种多样性指数（Simpson指数和Shannon指数）、均匀度指数（Pielou均匀度）和物种丰富度,对佛坪国家级自然保护区主要高等植物群落物种多样性进行了测度。结果表明：森林群落的多样性程度高于灌丛和草甸,落叶阔叶林高于针叶林,栎林高于杨桦林。群落物种多样性有随海拔高度的升高而降低的趋势。物种多样性在森林群落垂直结构上的分布特点,表现为一般乔木层与灌木层接近但低于草本层。