Effect of allelopathic compounds produced by Cistus ladanifer on germination of 20 Mediterranean taxa

In order to analyze the extent to which allelopathic action of Cistus ladanifer may influence the successional progression towards Mediterranean sub-climacic shrublands and the geographical distribution of other species, the inhibitory effect of Cistus ladanifer extracts on the germination of 20 Mediterranean species was analyzed. Five of the species tested were characteristic of maquis sub-climacic shrublands: Arbutus unedo, Adenocarpus argyrophyllus, Phillyrea angustifolia, Phillyrea latifolia, and Rhamnus alaternus. Tests were also carried out on 6 Cistaceae species in order to evaluate the auto-toxicity rate of allelopathic extracts: Halimium umbellatum subsp. viscosum, Halimium ocymoides, Cistus ladanifer, Cistus salvifolius, Cistus monspeliensis, and Cistus populifolius. Nine herbaceous species sharing the natural habitat with C. ladanifer were also examined. Results confirmed a clear inhibitory and delaying effect of aqueous C. ladanifer-leaf extracts on the germination of P. angustifolia, P. latifolia, R. alaternus, H. ocymoides, C. populifolius, Erysimum lagascae, Brassica barrelieri, Silene tridentata, and Moricandia moricandioides. Assays with soil collected below the canopy of the C. ladanifer community showed more pronounced inhibitory effect on sub-climacic shrub species than the aqueous extracts. In contrast, the opposite pattern was detected when analyzing the allelopathic effect of natural soil on Cistaceae and herbaceous species. Allelopathic compounds produced by C. ladanifer showed little auto-toxicity. The inhibitory effect of phytotoxic compounds accumulated in the jaral soil upon germination of A. unedo, B.␣barrelieri, and M. moricandioides was eliminated by heating soil at 150 °C for 10 min. Phenolic compounds (i.e. ferulic, p-hydroxybenzoic, vanillic, p-coumaric, and caffeic acids) and terpenes (i.e. α and β-pinene) with allelopathic documented effect were detected in the aqueous extracts and soil samples used in the analyses. We suggest that the allelopathic effect of C. ladanifer may influence the composition and structure of Mediterranean communities where the species is present, since it hinders the establishment of some sub-climacic species and may reduce the area occupied by numerous herbaceous species.     

Potential allelopathic effect of neo-clerodane diterpenes from Teucrium chamaedrys (L.) on stenomediterranean and weed cosmopolitan species

The allelopathic effects of neo-clerodane diterpenes, isolated from Teucrium chamaedrys (L.), have been evaluated on the seed germination and seedling growth of four coexisting Mediterranean species (Dactylis hispanica, Petrorhagia velutina, Phleum subulatum and Petrorhagia saxifraga) and two cosmopolitan weeds (Amaranthus retroflexus and Avena fatua). All of the structures have been elucidated on the basis of their spectroscopic features. The bioassays data, analyzed by principal component analysis, showed more negative effects on weeds respect to coexisting species. Moreover D. hispanica, P. velutina, P. subulatum showed both stimulating or inhibiting effects depending on the type of metabolite and the concentration used in the test.     

Interference between Hieracium pilosella and Arrhenatherum elatius in colliery spoils of north of France

Summary On colliery heaps in northern France, a tall grassland community dominated by Arrhenatherum elatius, give place to a thin grassland community in which Hieracium pilosella is very abundant. It has been claimed that Hieracium pilosella is an allelopathic species and this phenomenon has been investigated as an explanation of this phase of plant succession. The importance of osmotic pressure in tested plant extracts is demonstrated and may be responsible for presumed allelopathy. Two phytotoxic compounds have been revealed in roots+rhizomes of Hieracium pilosella (umbelliferon and apigenin-glucoside). A third phytotoxic compound was exuded by roots in hydroponic cultures (7-glucoside-umbelliferon or skimin). However no toxicity of soil has been found and no phytotoxic compounds appeared to be present in the soil under Hieracium pilosella. Experimental mixed cultures (sterile or non-sterile conditions) reveal suppression of Hieracium pilosella by Arrhenatherum elatius rather than the reverse. Allelopathy cannot be invoked to explain this plant succession.     

Root plasticity in Mediterranean herbaceous species

Abstract

Root plasticity has been largely studied on herbaceous species of north European temperate flora and is defined as the ratio between root depth in dry soils and root depth in wet soils. In summer dry habitats such as Mediterranean environments, the soil water deficit is a common feature to which root systems of plant species should adapt to improve their ecological efficiency. The aim of this study was to compare root plasticity in annual Mediterranean species that regenerate exclusively from seeds, and herbaceous perennial Mediterranean species that use dual regeneration strategies. Root plasticity of ten herbaceous species, six perennials and four annuals, was compared in this study. The annuals species studied occur in lowland Mediterranean grasslands referred to Tuberarietea guttatae class (Dasypyrum villosum, Lophochloa pubescens, Ornithopus compressus, Rumex bucephalophorus), while the perennial species occur in montane sub-Mediterranean grasslands referred to Festuco brometea (Bromus erectus, Festuca ovina., Lotus corniculatus., Minuartia verna, Sanguisorba minor, Thymus longicaulis). The examined species were subjected to water stress according to standard methods applied in comparative ecology, i.e., half of the seedlings of each species received 20 ml de-ionized water daily for three weeks, while the other half did not. After seedling harvesting the following parameters were analysed: (i) total root length; (ii) root length in the first 10 cm of soil; (iii) shoot height; (iv) root biomass in the first 10 cm of soil; (v) shoot biomass; (vi) shoot and root plasticity. Results show that root plasticity increased significantly in dual-regenerator sub-Mediterranean mountain species.     

Fragmentation pathways of acylated flavonoid diglucuronides from leaves of Medicago truncatula

Introduction – Flavonoids are important plant compounds occurring in tissues mostly in the form of glycoconjugates. Most frequently the sugar moiety is comprised of mono‐ or oligosaccharides consisting of common sugars like glucose, rhamnose or galactose. In some plant species the glycosidic moiety contains glucuronic acid and may be acylated by phenylpropenoic acids. Methodology – Flavonoid glyconjugates were extracted from leaves of Medicago truncatula ecotype R108 and submitted to analysis using high‐performance liquid chromatography combined with high‐resolution tandem (quadrupole‐time of flight, QToF) mass spectrometry. Results – The studied leaf extracts contained 26 different flavonoid glycosides among which 22 compounds were flavone (apigenin, luteolin, chrysoeriol and tricin) glucuronides and 13 were acylated with aromatic acids (p‐coumaric, ferulic or sinapic). The fragmentation pathways observed in positive and negative ion mass spectra differed substantially between each other and from these of flavonoid glycosides which did not contain acidic sugars. The application of high‐resolution MS techniques allowed unequivocal differentiation between ions with the same nominal m/z values containing different substituents (e.g. ferulic acid or glucuronic acid). Eleven of the identified flavonoids have not been reported previously in this species. Perspectives – The presented unique fragmentation pathways of flavonoid glucuronates enable detection of these compounds in tissue extracts from different plant species. Copyright © 2009 John Wiley & Sons, Ltd.     

Infection with the fungal endophyte Epichloë festucae may alter the allelopathic potential of red fescue

Red fescue (Festuca rubra) is a perennial grass used as both forage and turfgrass. Asymptomatic plants of this species are systemically infected by the fungal endophyte Epichloë festucae, which has a beneficial effect on the infected plants. The aim of this study was to determine the effect of the endophyte Epichloë festucae on the allelopathic potential of F. rubra against four associated pasture species that are also considered as weeds in lawns, Trifolium pratense, Trifolium repens, Lotus corniculatus and Plantago lanceolata. Two experiments were designed to evaluate the allelopathic effect of extracts from the roots and leaves of endophyte‐infected (E+) and non‐infected (E?) plants on the germination and seedling growth of the four target species. Regardless of the endophyte status of the host plant, leaf extracts elicited a stronger reduction in germination and seedling growth than root extracts. Extracts from E+ plants reduced the speed of germination index of Trifolium spp. to a greater extent than those from E? plants. Radicle length of the target species was the parameter most affected by the presence of the endophyte in F. rubra. Root extracts from E+ plants had a greater inhibitory effect on the radicle growth of the target species than did root extracts from E? plants. A greater concentration in total phenolic compounds was found in the roots of E+ plants than of E?; however, this difference was not observed in the leaves. Thus, the allelopathic potential of F. rubra is altered in infected plants.     

Seasonal dependence and functional implications of macrophyte–phytoplankton allelopathic interactions

Invasive plant species such as Ludwigia hexapetala might have a competitive advantage if they produce allelopathically active compounds against primary producers. Both phytoplankton and plant community structure may be affected due to different, species‐specific sensitivity to allelochemicals. Moreover, such allelopathic interactions could vary over the year depending on (i) the plant's phenological stage and (ii) the abilities of the native macrophytes to suppress—or the non‐native macrophytes to stimulate—the non‐native macrophyte population. We tested the allelopathic effects of aqueous leaf extracts of L. hexapetala on the photosynthetic activity of three target phytoplankton strains (Scenedesmus communis, a toxic Microcystis aeruginosa strain and a non‐toxic Microcystis aeruginosa strain) over three seasons of development (spring, summer and autumn). We also tested seasonal allelopathic effects of aqueous leaf extracts of both L. hexapetala (i.e. the non‐native invasive species) and the native Mentha aquatica on L. hexapetala seed germination. Finally, we identified three main secondary compounds present in the aqueous leaf extracts of L. hexapetala and we tested each individual compound on the phytoplankton's photosynthetic activity and on L. hexapetala seed germination. We observed marked seasonal and species‐specific patterns of L. hexapetala allelopathy on phytoplankton. The photosynthetic activities of S. communis and the toxic M. aeruginosa strain were stimulated by L. hexapetala aqueous leaf extracts in autumn and spring, respectively, whereas the non‐toxic M. aeruginosa strain was strongly inhibited in these two seasons. In summer, photosynthesis of all phytoplankton strains was inhibited. The germination rate of L. hexapetala seeds was stimulated by both L. hexapetala and M. aquatica aqueous leaf extracts, especially in summer, concomitant with the strong negative effects observed on the three phytoplankton strains. Three flavonoid glycosides (myricitrin, prunin and quercitrin) were identified as the main secondary compounds present in the L. hexapetala aqueous leaf extracts. The photosynthetic activity of S. communis was slightly stimulated by the three compounds. The photosynthetic activity of the toxic M. aeruginosa strain was stimulated by myricitrin and quercitrin, whereas that of the non‐toxic M. aeruginosa strain was inhibited by prunin. Finally, the germination rate and the germination velocity of L. hexapetala seeds were stimulated by myricitrin and prunin. These findings suggest that L. hexapetala could favour the photosynthetic activity of toxic cyanobacteria in spring and reduce their photosynthetic activity in summer, potentially leading to drastic changes in the phytoplankton communities and therewith ecological functioning of invaded ponds. Moreover, the stimulation of its seed germination could give a strong competitive advantage to L. hexapetala, thus promoting its invasiveness.     

The response of Mediterranean herbaceous community to soil disturbance by native wild boars

Native wild boar (Sus scrofa lybicus) populations in Israel increased in the last decades, and their rooting activity presents an apparent severe disturbance that may affect herbaceous plant communities. We studied the extent of wild boar rooting and its effect on herbaceous vegetation in an east Mediterranean garrigue. We compared the effects of rooting soil disturbance (RSD) between summer, winter, and RSD-free control plots on herbaceous plants. RSD affected four percent of the area covered by herbaceous vegetation in winter and spring, and only 2 % in summer. Summer RSD increased herbaceous species diversity in the following spring by decreasing the abundance of the dominant species, but it did not affect total herbaceous biomass. Winter RSD lowered herbaceous biomass but did not affect herbaceous plant abundance or diversity. We conclude that Mediterranean herbaceous plant community appears to be resilient to RSD, causing only minor changes in species composition and small decrease of their biomass. The contrast between the relatively large extent of wild boars RSD, and its limited impact on the herbaceous plant community, can be attributed to the long mutual evolutionary history of wild boars and these vegetation communities.     

Antioxidant efficacy of iridoid and phenylethanoid glycosides from the medicinal plant Teucrium chamaedris in cell-free systems

Twelve glycosides, seven iridoids and five phenylethanoids, have been isolated from leaf and root methanolic extracts of Wall Germander (Teucrium chamaedrys), a Mediterranean species historically used as a medicinal plant. Among them, three iridoid and one phenylethanoid glycosides have been isolated and characterized for the first time. All of the structures have been elucidated on the basis of their spectral data, especially 1D and 2D NMR experiments.The antioxidative properties of pure metabolites, as well as of crude organic extracts of the plant, have been analyzed on the basis of their DPPH radical scavenging capability. The antioxidant capacity in cell-free systems of the isolated metabolites was carried out by measuring their capabilities to inhibit the synthesis of thiobarbituric acid reactive species in assay media using as oxidable substrates a vegetable fat and the pentose sugar 2-deoxyribose and to prevent oxidative damage of the hydrosoluble bovine serum albumin (BSA) protein. Phenylethanoid glycosides resulted efficacious DPPH radical, while iridoid glycosides prevent massively the 2-deoxyribose and BSA oxidations in assay media.     

黄土丘陵区草本群落演替中先锋种群茵陈蒿浸提液的化感作用

为探索自然演替中植被群落结构与化感作用之间的关系,以黄土丘陵区自然演替中先锋种群茵陈蒿为研究对象,通过种子萌发试验,分析演替初期优势种群茵陈蒿浸提液(甲醇浸提液和水浸提液)对自身以及伴生种种子萌发以及幼苗生长的影响,从化学生态学角度解释演替初期群落结构形成的原因。结果表明,茵陈蒿浸提液对3种伴生种(铁杆蒿、白羊草和达乌里胡枝子)的种子萌发均有显著化感作用,低浓度(0.002g/m L)时表现为促进或轻微的抑制作用,高浓度(0.2g/m L)时为较强的抑制作用;不同部位茵陈蒿浸提液的化感作用不同,相比之下,地上部的抑制作用更为强烈,其浸提液均抑制铁杆蒿、白羊草和达乌里胡枝子的种子萌发,尤其在浓度为0.2 g/m L时,达到完全抑制;根系甲醇浸提液对铁杆蒿种子萌发的抑制作用要强于同浓度下的水浸提液,而地上部水浸提液对受体植物根芽的作用大于甲醇浸提液。茵陈蒿对于自身具有一定的抑制作用,表现为高浓度(0.2和0.02 g/m L)的水和甲醇浸提液抑制自身种子萌发和幼苗生长。研究结果说明化感作用可能是该地区在演替前期形成以茵陈蒿为优势种植被群落的重要原因之一。创新点:从化学生态学的角度解释了黄土丘陵区植被演替初期植物之间的关系以及群落结构形成的原因,为认识自然恢复的内在机理提供了新的视角。     

物种多样性及生物量与地下水位的关系——以海流兔河流域为例

以3条样带上117块植被群落调查样方为基础资料,研究了海流兔河流域植被物种多样性及生物量与地下水位之间的关系。结果表明:1)地下水位高低及地貌类型均会影响草本层植物群落组成及优势种构成。滩地样地中,随地下水位降低,优势草本的更替方向为寸草,芨芨草,马蔺,狗尾草,碱茅;沙坡样地中,优势草本的更替方向为大针茅,沙鞭,沙蓬,沙打旺。2)地下水位为1.5 m时是草本植物群落生长发育最适宜区域,物种多样性及丰富度达到最大,而灌木层物种多样性及丰富度随地下水位下降呈现波动变化的特征;当地下水位埋深小于5.0 m时,草本层物种多样性及丰富度明显高于灌木层,在地下水位埋深大于5.0 m时,草本层物种多样性指数开始出现低于灌木层的现象。3)草本植物多样性及丰富度和生物量之间关联性不强,滩地样地中,草本层地上生物量及地下生物量在地下水位为1.8 m时具有最大值,但植物群落结构较为单一;沙坡样地中,地上生物量最大值出现在地下水位为5.0 m的区域内,而地下生物量最大值出现在地下水位为3.5 m时。综上,物种多样性、地上及地下生物量与地下水位都不是简单的线性关系,而是有一个最适水位;高于或低于这个最适水位,多样性和生物量都会下降。     

Potential allelopathic effect of <Emphasis Type="Italic">Eucalyptus</Emphasis><Emphasis Type="Italic">grandis</Emphasis> across a range of plantation ages

Allelopathy of the eucalypt has been considered as an important mechanism for the biodiversity reduction in the eucalypt plantation. To understand the allelopathic potential of the eucalypt (Eucalyptus grandis) roots and rhizosphere soil along a chronosequence (2, 4, 6, 8, 10 years), the germination and growth characteristics of three plant species (Raphanus sativus, Phaseolus aureus, and Lolium perenne) growing nearby or beneath the eucalypt plantations were measured. The results showed that aqueous extract of E. grandis root suppressed the germination and early seedling growth of the target plants. The younger E. grandis exhibited a comparatively stronger allelopathic potential. The highest dose root extracts from 4 years old E. grandis showed the strongest inhibitory effects on the germination rates of the target species, the inhibitory rates were about 48, 51.2, and 56.56% for R. sativus, P. aureus, and L. perenne, respectively. However, present biotests of rhizosphere soils from 6, 8, and 10-year-old plantations exhibited a remarkable stimulative effect on L. perenne, which indicated that the soil might neutralize or dilute allelopathic agents with the increase of plantation age. In addition, according to GC–MS analysis, more allelopathic potential compounds were found in the rhizosphere soil and roots of younger E. grandis plantation. Moreover, more allelochemicals were obtained from soil than from roots. The allelopathic compounds in roots and rhizosphere soil may play important roles in allelopathy of E. grandis plantation. More attention should be paid to the younger E. grandis plantations for the relative higher allelopathic effects.     

Potential allelopatic effects of stilbenoids and flavonoids from leaves of Carex distachya Desf.

The potential allelopathic effects of 14 stilbenoids and five flavonoids, isolated from leaves of Carex distachya Desf., were evaluated on the seed germination and seedling growth of three coexisting Mediterranean species (Dactylis hispanica, Petrorhagia velutina, and Phleum subulatum). The structures of the metabolites have been elucidated on the basis of their spectroscopic features (1D and 2D NMR experiments and EI–MS and ESI–MS data). The bioassays showed species-specific effects of the metabolites from C. distachya, specially on the plant growth (root and shoot elongation) which resulted significantly stimulated or inhibited at 10⁻⁴ M concentration. The effects on root elongation is generally greater than the shoot growth at all the tested concentrations (10⁻⁴–10⁻⁸ M). Cluster of biological data showed interesting relationships between the chemical structures of the compounds and their biological effects.     

Flavonoids exclusively present in mycorrhizal roots of white clover exhibit a different effect on arbuscular mycorrhizal fungi than flavonoids exclusively present in non-mycorrhizal roots of white clover

Abstract

The flavonoids 5,6,7,8,9-hydroxy chalcone, 3,7-hydroxy-4′methoxy flavone, 5,6,7,8-hydroxy-4′-methoxy flavone and 3,5,6,7,4′-hydroxy flavone can be detected only in non-mycorrhizal roots of white clover, but not in mycorrhizal roots, whereas the flavonoids acacetin, quercetin and rhamnetin are only present in mycorrhizal roots. We tested the effect of several concentrations of these compounds on spore germination, hyphal growth, hyphal branching, formation of clusters of auxiliary cells and of secondary spores of the arbuscular mycorrhizal fungi Gigaspora rosea, Gigaspora margarita, Glomus mosseae and Glomus intraradices. Our results indicate that depending on the flavonoid, the tested compounds are involved at different stages in the regulation of mycorrhization. This hypothesis is strengthened by their differing effect on several AM fungal growth parameters. Furthermore, our study provides more data on the AM fungus genus/species specificity of flavonoids.     

Floristic composition and floral phenology of the Mediterranean batha of Ariel,Samaria

Field observations over a three-year period were used to document the floristic composition, flowering and fruiting sequences of the Sarcopoterium spinosa Mediterranean batha of Ariel. This plant community was found to be species-rich, with high percentages of annuals, bushes and geophytes, low percentages of herbaceous plants, climbers and trees, and ten species considered rare in Israel. Typical Mediterranean characteristics were observed in the S. spinosa batha: spring flowering reaching a peak in April, small between-year variation in flowering and fruiting, most species having Mediterranean distribution, and partial resistance to fire.     

The herb community of a tropical forest in central Panamá: dynamics and impact of mammalian herbivores

Mammals are hypothesized to either promote plant diversity by preventing competitive exclusion or limit diversity by reducing the abundance of sensitive plant species through their activities as browsers or disturbance agents. Previous studies of herbivore impacts in plant communities have focused on tree species and ignored the herbaceous community. In an experiment in mature-phase, tropical moist forest sites in central Panamá, we studied the impact of excluding ground-dwelling mammals on the richness and abundance of herbs in 16, 30×45-m plots. Within each plot, we censused the herbaceous community in 28, 2×2-m subplots (1,792 m² total area sampled). We identified over 54 species of herbs averaging 1.21 ramets m⁻² and covering approximately 4.25% of the forest floor. Excluding mammals for 5 years had no impact on overall species richness. Within exclosures, however, there was a significant two-fold increase in the density of rare species. Overall herbaceous density and percent cover did not differ between exclosures and adjacent control plots, although cover did increase over time. Mammalian exclusion significantly increased the total cover of three-dominant herb species, Pharus latifolius, Calathea inocephala, and Adiantum lucidum, but did not affect their density. This study represents one of the most extensive herbaceous community censuses conducted in tropical forests and is among a few that quantify herbaceous distribution and abundance in terms of both density and cover. Additionally, this work represents the first community level test of mammalian impacts on the herbaceous community in a tropical forest to date. Our results suggest that ground dwelling mammals do not play a key role in altering the relative abundance patterns of tropical herbs in the short term. Furthermore, our results contrast sharply with prior studies on similar temporal and spatial scales that demonstrate mammals strongly alter tree seedling composition and reduce seedling density. Thus, we question the pervasiveness of top–down control on tropical plant communities and the paradigm that defaunation will inexorably lead to widespread, catastrophic shifts in plant communities.     

Ecosystem disturbance reduces the allelopathic effects of Empetrum hermaphroditum humus on tundra plants

Question: Do naturally occurring ecosystem disturbances interfere with allelopathic effects and alleviate growing conditions for plants typical of more productive ecosystem states? Location: An unproductive tundra ecosystem in Northern Fennoscandia. Methods: We designed a factorial phytotron experiment to monitor the growth of seedlings of two herbaceous species in undisturbed and disturbed humus of the dominant dwarf shrub Empetrum hermaphroditum, which releases allelopathic substances that accumulate in soil over time. Herbivore defecation and wildfire are two major ecosystem disturbances likely to alleviate effects of these allelopathic substances. Humus and seeds of herbaceous species were sampled from Empetrum‐dominated heaths. Disturbance effects on humus were simulated by adding reindeer faeces and by low‐severity burning. Results: The concentration of the allelopathic substance batatasin‐III in Empetrum humus was 0.32±0.16 (SE) μg g^?1, which is similar to previous reports from boreal areas. Reindeer faeces addition and burning treatments to Empetrum humus caused three‐ and five‐fold increases in growth of the herbaceous species Avenella flexuosa and Solidago virgaurea respectively. Changes in soil chemistry caused by the disturbance, i.e. increased pH and nutrient availability, likely interfered with allelopathic effects and improved conditions for growth. Conclusions: Humus from Empetrum‐dominated tundra areas is infertile for seedlings of local herbaceous plants. Simulated herbivore defecation and wildfire can alleviate this infertility. Based on our results, we discuss the potential role of these naturally occurring disturbances in switching vegetation composition from Empetrum to herbaceous dominance, i.e. from an unproductive to a more productive tundra ecosystem.     

Allelopathic invasive tree (<Emphasis Type="Italic">Rhamnus cathartica</Emphasis>) alters native plant communities

Many plants release allelopathic chemicals that can inhibit germination, growth, and/or survival in neighboring plants. These impacts appear magnified with the invasion of some non-native plants which may produce allelochemicals against which native fauna have not co-evolved resistance. Our objective was to examine the potential allelopathic impact of an invasive non-native shrub/tree on multiple plant species using field observation and experimental allelopathy studies. We surveyed and collected an invasive, non-native tree/shrub (Rhamnus cathartica) at Tifft Nature Preserve (a 107-ha urban natural area near Lake Erie in Buffalo, NY). We also surveyed understory plant communities in the urban forest to examine correlations between R. cathartica abundance and local plant community abundance and richness. We then used experimental mesocosms to test if patterns observed in the field could be explained by adding increased dosages of R. cathartica to soils containing five plant species, including native and non-native woody and herbaceous species. In the highly invaded urban forest, we found that herbaceous cover, shrubs and woody seedlings negatively covaried with R. cathartica basal area and seedlings density. In the mesocosm experiments, R. cathartica resulted in significant decreases in plant community species richness, abundance, and shifted biomass allocation from roots. Our results provide evidence that R. cathartica is highly allelopathic in its invaded range, that R. cathartica roots have an allelopathic effect and that some plant species appear immune. We suggest that these effects may explain the plant’s ability to form dense monocultures and resist competitors, as well as shift community composition with species-specific impacts.     

东祁连山灌丛凋落叶水浸提液对垂穗披碱草种子萌发和幼苗生长的影响

为了解灌丛凋落叶在灌草群落结构维持中可能存在的潜在化感作用,以东祁连山3种优势灌木和灌下优势草种垂穗披碱草(Elymus nutans)为供试材料,分析了不同浓度(0.01 g/L、0.025 g/L、0.05 g/L、0.075 g/L、0.1 g/L)的金露梅(Potentilla fruticosa)、川滇柳(Salix rehderiana)、头花杜鹃(Rhododendron capitatum)及灌间草本的凋落叶水浸提液,对垂穗披碱草种子萌发、幼苗形态和生理指标的影响。结果表明：(1)垂穗披碱草种子发芽率与发芽势在金露梅与川滇柳凋落叶浸提液处理下呈“低促高抑”的浓度效应,在灌间草本凋落叶浸提液处理时表现为先升后降,而头花杜鹃凋落叶浸提液处理时均下降,并在浓度超过0.075 g/L时种子不发芽。(2)灌丛凋落叶浸提液对垂穗披碱草幼苗根长与干重均表现出抑制作用,且随浓度增大而增强;金露梅、川滇柳与灌间草本凋落叶浸提液对垂穗披碱草幼苗苗高表现出“低促高抑”的浓度效应;而头花杜鹃凋落叶浸提液处理对垂穗披碱草幼苗鲜重与苗高均呈抑制作用。(3)垂穗披碱草幼苗CAT、SOD活性随着浸提液...     

Allelopathic effects of three plant invaders on germination of native species: a field study

The ability of some invasive plant species to produce biochemical compounds toxic to native species, called allelopathy, is thought to be one of the reasons for their success when introduced to a novel range, an idea known as the Novel Weapons Hypothesis. However, support for this hypothesis mainly comes from bioassays and experiments conducted under controlled environments, whereas field evidence is rare. In a field experiment, we investigated whether three plant species invasive in Europe, Solidago gigantea, Impatiens glandulifera and Erigeron annuus, inhibit the germination of native species through allelopathy more than an adjacent native plant community. At three sites for each invasive species, we compared the germination of native species that were sown on invaded and non-invaded plots. Half of these plots were amended with activated carbon to reduce the influence of potential allelopathic compounds. The germination of sown seeds and of seeds from the seedbank was monitored over a period of 9 weeks. Activated carbon generally enhanced seed germination. This effect was equally pronounced in invaded and adjacent non-invaded plots, indicating that invasive species do not suppress germination more than a native plant community. In addition, more seeds germinated from the seedbank on invaded than on non-invaded soil, probably due to previous suppression of germination by the invasive species. Our field study does not provide evidence for the Novel Weapons Hypothesis with respect to the germination success of natives. Instead, our results suggest that if invasive species release allelopathic compounds that suppress germination, they do so to a similar degree as the native plant community.