Variation of plant diversity components in different scales in relation to grazing and climatic conditions

Background: Understanding the role of livestock grazing on plant diversity can be improved by an accurate measurement of diversity at all hierarchical scales due to the changeability of diversity components in space.

Aims: We evaluated the effects of grazing on plant species diversity at different scales of all common and rare species in two regions that have different climatic conditions (arid vs. semi-arid).

Methods: In each region, we collected abundant data of plant species from a nested sampling design that consisted of local (80 plots) and regional (16 sites) scales. We partitioned total species diversity (γ) into within plots (α_l), among plots (β_l) and among sites (β₂) using the additive partitioning.

Results: Diversity among sites contributed the most to total diversity for all and rare plant species in both regions. In addition, α₁ and β₁ diversities in ungrazed areas were greater than those in grazed areas for all and common species in both climates.

Conclusion: Abandonment of grazing after 10 years resulted in significant regeneration of common species at the local scale, with no change in rare species. We conclude that low grazing intensity is likely to be an important tool for conservation of plant diversity in which all scales should be considered.     

Distribution of allozymic alleles and genetic diversity in the American Barley Core Collection

A survey of allozymic alleles and genetic diversity was made for 151 accessions of the American Barley Core Collection. A total of 25 alleles at ten loci were observed. Two loci were monomorphic. The average diversity index for individual loci ranged between 0.026 and 0.649. Most significant differences in allelic frequency and genetic diversity value were found between spring and winter barley. Spring barley showed a greatly higher average diversity than winter barley (t=2.124, P=0.071). The smallest differences in allelic frequencies and diversity values were observed between the two geographical regions, North and South America. Rare alleles were detected only in a few accessions. Seven rare alleles were associated with spring barley. The genetic similarities among the 151 accessions ranged from 0.20 to 1.00, which showed that a high level of genetic variability exists in this set of core accessions. Cluster analysis and principal coordinate analysis did not give clear-cut separation of different types of barley, but most of the winter barley accessions were closely associated. Received: 7 April 2000 / Accepted: 13 June 2000     

Genetic diversity among East Asian accessions of the barley core collection as revealed by six isozyme loci

 Studies of allelic variations at six isozyme loci revealed genetic diversity of 380 East Asian accessions of the Barley Core Collection. Genetic variation was found in both cultivars and landraces in different regions. Allelic variations at the Aco-1 and Aco-2 loci were detected for East Asian barley for the first time. Moreover, the Aco-1 locus displayed the highest genetic diversity among the six loci assayed. Indian cultivars showed the highest diversity, followed by Korean and Chinese cultivars. Landraces from Bhutan and Nepal showed the lowest diversity. Cultivars had generally higher diversity than landraces within as well as among regions. The cluster analysis of genetic identity showed that all landraces from different countries can be placed in one group; the cultivars from Japan, India and Korea each form independent groups. Gpi-1 Gu, Pgd-1 Tj, Aco-1 Si, Ndh-2 D and Aco-2 A were rare alleles found in only a few accessions of 6-rowed barley. The Pgd-2 Tn allele was very rare in East Asian accessions. Received: 29 July 1998 / Accepted: 2 November 1998     

Genetic and phenotypic variation,dispersal limitation and reproductive success in the invasive herb Eschscholzia californica along an elevation gradient in central Chile

Background: Reductions of genetic diversity and phenotypic changes in invasive plants are often observed to occur at high elevations. Genetic/phenotypic changes of invasive plants along elevation help to understand mechanisms of the presumed resistance of mountain ecosystems to invasion.

Aims: To assess genetic variability and phenotypic plasticity along an elevation gradient of Eschscholzia californica in the Andes, central Chile.

Methods: Eleven microsatellites were used to describe the genetic structure and the allelic diversity individuals, distributed at three elevations and two sites. We assessed the number of flowers per plant, floral biomass, leaf area, number of leaves, vegetative biomass and plant height of plants at each elevation.

Results: Genetic diversity as genetic structure did not decrease with elevations. Plant height and flower numbers decreased while leaf number and vegetative biomass increased with elevation. The ratio of the number of flowers to vegetative biomass, decreased significantly with elevation.

Conclusions: Strong genetic differences among elevations and similar genetic diversity along elevation do not suggest dispersal limitation to higher elevation. Reduction of reproductive and vegetative traits concomitantly with an increase of the reproductive cost suggests reproductive stress with increasing elevation, reducing the invasiveness of this species to higher elevation.     

Allelopathic vs. autotoxic potential of a grassland weed—evidence from a seed germination experiment

ABSTRACT

Background: Mechanisms affecting invasiveness of non-indigenous species have received much attention. Few studies have investigated invasions by native plants. Invasive native species such as common ragwort (Jacobaea vulgaris) may become noxious weeds. They challenge farming and nature conservation by outcompeting fodder plants or rare herbs. One mechanism that can result in outcompeting plants is by allelopathy.

Aim: We evaluated the potential of J. vulgaris to suppress germination in common and rare grassland species by allelopathy.

Methods: In a germination chamber experiment, we exposed 22 species and J. vulgaris itself to ragwort leachate. We controlled for osmotic effects by germination tests in mannitol solution and water. We assessed germination percentage—time —synchrony and radicle length.

Results: Leachate reduced germination percentage, germination time, synchrony and radicle length. These effects were similar for J. vulgaris, indicating autotoxicity. Rare species germinated less than common species but were not more sensitive to the phytotoxic effects of J. vulgaris. Restraining effects of the leachate were similar to the mere osmotic effect.

Conclusion: Our results question allelopathy as the main driving mechanism behind J. vulgaris gaining dominance. However, the impact of J. vulgaris might depend on the composition of the invaded plant community due to species-specific effects.     

Weed–barley interactions affect plant acceptance by aphids in laboratory and field experiments

Increased botanical diversity can lead to suppression of insect pests. One route by which botanical diversity is increased in crops is through the occurrence of weeds, which increasingly interact with crop plants as organic production expands. However, the mechanisms by which this might affect insect herbivores are poorly understood. This study examined whether volatile chemical interactions between weeds and barley, Hordeum vulgare L. (Poaceae), can affect plant acceptance by the bird cherry oat aphid, Rhopalosiphum padi L. (Hemiptera: Aphididae). In laboratory experiments, exposure of barley to volatiles from Chenopodium album L. (Amaranthaceae) and Solanum nigrum L. (Solanaceae) resulted in significantly reduced aphid acceptance compared with unexposed plants. In a series of field experiments in which the occurrence of weeds was manipulated in plots of barley, significantly lower aphid acceptance was recorded on barley plants grown in plots with C. album compared with barley plants in weedless plots. The results indicate that interaction between weeds and barley can affect aphid–plant interactions in the field as well as in the laboratory and provide further evidence that the effects of chemical interactions between visibly undamaged plants can extend to higher trophic levels.     

Searching behaviour of the sevenspotted ladybird, Coccinella septempunctata– effects of plant-plant odour interaction

In the present study the main aim was to investigate the odour mechanisms affecting habitat preferences of Coccinella septempunctata (L.). In a field study, the frequency of adult C. septempunctata was higher in barley plots containing high densities of the common weeds Cirsium arvense (L.) Scop. and Elytrigia repens (L.) Nevski. than in control plots with only barley. In olfactometer experiments in the laboratory, adult C. septempunctata showed a significantly more positive response to mixed odours of barley and each of the two weeds than to barley alone. Ladybirds responded differently to barley plants that were previously exposed to volatiles from the two weeds. The E. repens -exposed barley plant lost its attractivity while the C. arvense -exposed barley plants maintained attractivity. As no aphids or pollen resources were present in the plots during the experiment, the results show that C. septempunctata responds to the botanical characteristics of the habitat even if no food resources are available. These results strongly suggest that olfactory cues and plant-plant communication from diversified plant stands can be important mechanisms in predator attraction to sites with a complex botanical diversity.     

东北丘陵区林地转型耕地对土壤编码碱性磷酸酶基因的细菌群落的影响

【目的】通过研究林地转型耕地对土壤编码碱性磷酸酶基因的细菌群落丰度、多样性和结构的影响,为丘陵区耕地长期施肥下农田土壤微生物多样性丧失的影响机制以及未来的退耕还林过程中土壤微生物多样性的提升和土地可持续利用研究提供一些基础数据和技术支撑。【方法】采用实时荧光定量PCR (real-time quantitative PCR,qPCR)和高通量测序技术解析土壤编码碱性磷酸酶基因的细菌群落的丰度、多样性和结构变化,并耦合土壤化学性质分析,明确土壤编码碱性磷酸酶基因的细菌群落丰度和多样性与土壤化学性质的关系以及关键的驱动因子。【结果】林地垦殖为农田后,长期施肥导致土壤酸化,pH从5.58降至4.72,而土壤速效磷则从2.49 mg/kg增至49.3 mg/kg。相应地,耕地土壤编码碱性磷酸酶基因的细菌群落的丰度和Shannon指数均显著低于林地。基于编码碱性磷酸酶的phoD基因(alkaline phosphatase-encoding gene)序列的物种分类表明,丘陵区土壤编码碱性磷酸酶基因的细菌群落的优势门为变形菌门(Proteobacteria)、蓝藻门(Cyanobacteria)、浮霉菌门(Planctomycetes)、放线菌门(Actinobacteria)、厚壁菌门(Firmicutes)和疣微菌门(Verrucomicrobia),其中林地土壤的蓝藻门的相对丰度显著高于耕地。耕地土壤的慢生根瘤菌属(Bradyrhizobium)和芽孢杆菌属(Bacillus)的相对丰度显著高于林地,而中慢生根瘤菌属(Mesorhizobium)、假单胞菌属(Pseudomonas)、Chlorogloea属、Gemmata属、Phormidesmis属和Pseudolabrys属的相对丰度显著低于林地。土壤编码碱性磷酸酶基因的细菌群落结构因林地转型耕地而发生显著改变。phoD基因丰度和Shannon指数与pH显著正相关,而与总磷、速效磷、硝态氮和铵态氮均显著负相关,其中土壤速效磷是这些影响因素中影响最强烈的,长期施用无机磷肥导致含碱性磷酸酶的土壤细菌群落对有机磷分解的能力退化。【结论】林地转型耕地加之长期施肥改变了土壤pH和速效磷,并在其他理化因子的协同驱动下,导致土壤编码碱性磷酸酶基因的细菌群落丰度、多样性和结构的显著变化。     

Diet of young Great Bustards Otis tarda in Spain: sexual and seasonal differences

Capsule Arthropods are the most important diet component of Great Bustards Otis tarda in the first months of life.

Aims To determine the diet composition of young Great Bustards in Spain.

Methods The diet was estimated by stomach content analysis (n?=?49).

Results Stomach contents' dry weight consisted of 33% arthropods, 30% green plant material and 23% seeds. Gastroliths were only found in summer and autumn. The diet composition changed significantly between seasons. In summer, diet consisted mainly of arthropods (50%), with green plant material being the main component in winter (56%). Volume of stomach contents and mean size of ingested arthropods were higher in males than in females. Diet composition did not differ between sexes. In summer, ground-dwelling and plant-visiting arthropods such as Mantidae, Tenebrionidae and caterpillars were the most abundant. In winter, weeds, legumes and cultivated seeds were more frequent than arthropods. Cereal plants were the least consumed in all seasons, although Barley and Wheat seeds played an important role during winter and autumn.

Conclusion The results highlight the importance of arthropods and weeds as a fundamental component of the diet of young Great Bustards. Because previous studies show that arthropods and weeds are usually more abundant in extensive farming, we recommend the implementation of agri-environmental measures in Great Bustard breeding areas.     

The impact of plant associations on Macrosteles quadrilineatus management in carrots

Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.     

Cereal density and N-fertiliser effects on the flora and biodiversity value of arable headlands

Modern intensive farming caused pronounced changes to the European arable flora. Many species adapted to less intensive traditional farming declined severely, as did the potential of unsown arable vegetation to support higher trophic levels. To reverse these trends, various agri-environment measures were introduced. One such measure is to manage cereal headlands as conservation headlands, involving strict restrictions on pesticide and fertiliser use. An additional modification to management which could reduce crop competition and thus deliver benefits to arable plants is cereal sowing at reduced rates. However, little is known about its benefits to rare and declining arable plants, or to species of value to higher trophic levels, and whether it can be implemented without concomitant increase in undesirable weeds. We set up identical two-factorial experiments in winter wheat and spring barley, combining a nitrogen fertiliser versus no fertiliser treatment with cereal sowing at economic rates versus sowing at rates reduced by 75 %, with added sowing of a mixture of rare arable species. Both experiments also included an uncropped but cultivated control equivalent to another agri-environment measure. Our results show that reduced cereal sowing in conservation headlands can benefit rare and declining species, as well as arable plant diversity, without necessarily resulting in a concomitant increase in undesirable weeds. While such benefits tended to be larger in uncropped cultivated controls, conservation headlands have the advantage of not requiring land being taken out of production. Moreover, as shown in this study, their benefits to arable plants can be maximised by reduced sowing.     

Antioxidants,Enzyme Inhibitors,and Biogenic Compounds in Grain Extracts of Barleys

The content of biogenic compounds and the biological activities of barley (Hordeum vulgare L.)‐grain extracts was evaluated. The sufficiently large and heterogeneous set of barley genotypes (100 accessions) enabled the selection of special genotypes interesting for potential industrial, pharmaceutical, and medicinal applications. Barley genotypes with the highest contents of phenols, phenolic acids, flavonoids, biogenic thiols, and amines, radical‐scavenging activity, as well as inhibitory activities of trypsin, thrombin, collagenase, urokinase, and cyclooxygenase were identified.     

Genetic interactions influence host preference and performance in a plant-insect system

Phytophagous insects generally feed on a restricted range of host plants, using a number of different sensory and behavioural mechanisms to locate and recognize their host plants. Phloem-feeding aphids have been shown to exhibit genetic variation for host preference of different plant species and genetic variation within a plant species can also have an effect on aphid preference and acceptance. It is known that genotypic interactions between barley genotypes and Sitobion avenae aphid genotypes influence aphid fitness, but it is unknown if these different aphid genotypes exhibit active host choice (preference) for the different barley genotypes. Active host choice by aphid genotypes for particular plant genotypes would lead to assortative association (non-random association) between the different aphid and plant genotypes. The performance of each aphid genotype on the plant genotypes also has the ability to enhance these interactions, especially if the aphid genotypes choose the plant genotype that also infers the greatest fitness. In this study, we demonstrate that different aphid genotypes exhibit differential preference and performance for different barley genotypes. Three out of four aphid genotypes exhibited preference for (or against) particular barley genotypes that were not concordant with differences in their reproductive rate on the specific barley genotype. This suggests active host choice of aphids is the primary mechanism for the observed pattern of non-random associations between aphid and barley genotypes. In a community context, such genetic associations between the aphids and barley can lead to population-level changes within the aphid species. These interactions may also have evolutionary effects on the surrounding interacting community, especially in ecosystems of limited species and genetic diversity.     

Genetic diversity of Darnel (Lolium temulentum L.) in Malo, Ethiopia depends on traditional farming systems

Genetic Diversity of Darnel (Lolium temulentum L.) in Malo, Ethiopia Depends on Traditional Farming Systems. Economic Botany 58(4):568–577, 2004. Darnel (Lolium temulentum L.) is a mimic weed associated with wheat and barley cultivation. Mimic weeds have evolved along with cultivated crops. Human impact on the genetic diversity of agricultural weeds was elucidated using darnel as a model. Three strains in each field in Gaitza village, Malo region, Ethiopia were randomly sampled, and the genetic composition of 120 samples was analyzed using RAPD analysis. Genetic diversity and distances were calculated using Nei’s analysis, and cluster analysis was performed. These results indicated the occurrence of seed migration among the fields and a high genetic diversity of darnel in this region. Crop seed exchange and contamination of crop seeds with darnel seeds lead to the unintended artificial gene flow of darnel. Because darnel seeds and seedlings resemble their associated crop seeds and seedlings, traditional methods of crop cultivation have the unintended consequence of conserving the genetic diversity of darnel.     

Pine invasion decreases density and changes native tree communities in woodland Cerrado

ABSTRACT

Background: Invasive plants can negatively impact native communities, but the majority of the effects of these invasions have been demonstrated only for temperate ecosystems. Tropical ecosystems, including the Cerrado, a biodiversity hotspot, are known to be invaded by numerous non-native species, but studies of their impacts are largely lacking.

Aims: Our research aimed at quantifying how Pinus spp. presence and density affected Cerrado plant communities.

Methods: We sampled areas invaded and non-invaded by Pinus spp. to determine if pine invasion affected native tree richness, diversity, evenness, and density. We also evaluated if community composition differed between invaded and non-invaded sites.

Results: We found invaded plots had lower native tree densities than non-invaded plots and that Pinus spp. invasions changed native tree communities by reducing native species abundances.

Conclusion: Invasive pines had negative impacts on the native Cerrado tree community by reducing native plant density and changing species abundances. Reduced density and abundance at early invasion stages can result in reduction in biodiversity in the long term.     

Islands and streams: clusters and gene flow in wild barley populations from the Levant

The domestication of plants frequently results in a high level of genetic differentiation between domesticated plants and their wild progenitors. This process is counteracted by gene flow between wild and domesticated plants because they are usually able to inter‐mate and to exchange genes. We investigated the extent of gene flow between wild barley Hordeum spontaneum and cultivated barley Hordeum vulgare, and its effect on population structure in wild barley by analysing a collection of 896 wild barley accessions (Barley1K) from Israel and all available Israeli H. vulgare accessions from the Israeli gene bank. We compared the performance of simple sequence repeats (SSR) and single nucleotide polymorphisms (SNP) marker data genotyped over a core collection in estimating population parameters. Estimates of gene flow rates with SSR markers indicated a high level of introgression from cultivated barley into wild barley. After removing accessions from the wild barley sample that were recently admixed with cultivated barley, the inference of population structure improved significantly. Both SSR and SNP markers showed that the genetic population structure of wild barley in Israel corresponds to the three major ecogeographic regions: the coast, the Mediterranean north and the deserts in the Jordan valley and the South. Gene flow rates were estimated to be higher from north to south than in the opposite direction. As has been observed in other crop species, there is a significant exchange of alleles between the wild species and domesticated varieties that needs to be accounted for in the population genetic analysis of domestication.     

Spatial patterns of species diversity in sand dune plant communities in Yucatan,Mexico: importance of invasive species for species dominance patterns

Background: Coastal ecosystems in Mexico remain understudied in spite of their ecological, economic and conservation value and are being impacted by human activities along the coast. Knowledge on spatial patterns of plant species distribution that helps preserve these fragile ecosystems is crucial.

Aims: We evaluated differences in species richness, species diversity and species dominance patterns in 16 plant communities as well as the degree to which differences were driven by climatic conditions in sandy dunes in Yucatán. We evaluated the importance of invasive species in mediating patterns of species diversity and species dominance patterns.

Results: We found wide variation in plant species richness, species diversity and species dominance patterns among communities that stems from broad climatic differences along dune systems. Invasive plants represent almost one-third of total species richness and seem to be drastically changing the species dominance patterns in these communities.

Conclusions: Regional climatic differences along the Yucatán north coast seems to be a major driver of plant diversity and species composition. Our findings suggest that invasive plants have successfully colonised and spread along the coast over the past 30 years. Even though invasive species do not alter spatial patterns of species diversity, they are becoming more dominant with potential detrimental consequences for native plants.     

Changes in the plant community of a Brazilian grassland savannah after 22 years of invasion by Pinus elliottii Engelm

Abstract

Background: The invasion by Pinus elliottii is one of the most serious threats to the remaining native cerrado vegetation in São Paulo State, Brazil, causing biodiversity losses yet to be evaluated. We conducted a study in an area where P. elliottii began establishing in 1988.

Aims: To estimate diversity losses in the plant community and to understand the floristic and structural changes resulting from pine tree invasion of grassland savannah.

Methods: All plants taller than 50 cm were sampled in 35 plots (64 m² each) within an area densely invaded by P. elliottii and in 10 plots in non-invaded grassland savannah. Density, species richness, diversity, ground cover and spatial distribution were compared by Wilcoxon tests, non-metric multidimensional scaling and Payandeh indices.

Results: Twenty-two years after the arrival of the first invasive trees (founders), the grassland savannah has become a dense pine forest with 12,455 individuals ha^?1, a basal area of 26.44 m² ha^?1, a sparse native woody understory comprised of 16 species (H'?=?0.44), density of 1210 individuals ha^?1 and the herbaceous layer totally absent.

Conclusions: Invasion by Pinus elliottii has completely changed the structure of the grassland savannah and caused severe plant diversity losses. Native species surviving the invasion in the understory do not typically represent the previous composition and functional traits of the native vegetation.     

The conservation of arable weeds at crop edges of barley fields in northeast Spain

The effects of weed control practices and fertilisation on weed flora and crop yield were evaluated in crop edges of barley fields in northeastern Spain. The study was carried out in four organic and four conventional barley fields. In each field, four permanent plots were delimited at the crop edge, and fertilisation and weed control treatments in a factorial design were applied over 3 years. Weed composition and the aboveground biomass of weeds and barley were recorded before the crop harvest in the first and the third year. We found relatively low values of species richness per field, as well as low values of weed biomass, especially in the organic crop edges (3.9% of total biomass). Weeds were significantly reduced by herbicide applications on conventional fields and were not affected by weed harrowing on organic fields or fertilisation. These results demonstrate that specific measures are needed to enhance biodiversity at crop edges both in organic and conventional fields. Our results also suggest that under Mediterranean conditions and among impoverished weed communities, limiting the use of herbicides is crucial to enhancing arable diversity and that, contrary to findings found in previous studies in temperate climates, fertilisation and weed harrowing have little effect on weeds.     

Long-term vegetation stability in northern Europe as assessed by changes in species co-occurrences

Background: The effect of the anticipated climate change on the stability of vegetation and the factors underlying this stability are not well understood.

Aims: Our objective was to quantify long-term vegetation changes in a range of habitats in northern Europe by exploring species co-occurrences and their links to diversity and productivity gradients.

Methods: We re-sampled vegetation in 16 arctic, mountain and mire sites 20 to 90 years after the original inventories. A site-specific change in species assemblages (stability) was quantified using species co-occurrences. Using a randomisation test we tested whether the changes observed were significantly greater than those expected by chance. Relationships between patterns in vegetation stability and time between surveys, numbers of plots, or species diversity and proxies for productivity, were tested using regression analysis.

Results: At most sites the changes in species co-occurrences of vascular plants and bryophytes were greater than those expected by chance. The changes observed were found to be unrelated to gradients in productivity or diversity.

Conclusions: Changes in species co-occurrences are not strongly linked to diversity or productivity gradients in vegetation, suggesting that other gradients or site-specific factors (e.g. land use or species interactions) may be more important in controlling recent compositional shifts in vegetation in northern Europe.