Initial Response of Butterflies to an Overstory Reduction and Slash Mulching Treatment of a Degraded Piñon-Juniper Woodland

Overstory reduction and slash mulching (ORSM) has been shown to be an effective means for increasing herbaceous cover and diversity in degraded piñon (Pinus edulis) and juniper (Juniperus monosperma) woodlands of north‐central New Mexico. Local fire history, tree age‐class structure, and grazing records suggest that many areas now occupied by dense piñon‐juniper woodlands were formerly more open, with grassy understories that supported well‐developed soils and a fire regime. At Bandelier National Monument, studies are evaluating the use of ORSM treatments as a restoration management tool. In 1999 and 2001, we evaluated the effects of an ORSM treatment implemented in 1997 upon butterfly abundance and species richness between a pair of treated and control watersheds. Butterfly abundance and species richness were significantly greater on the treated watershed in both years, and these measures were correlated with significant increases in forb and grass cover in the treated watershed. Five of the 10 most common nectar and larval host plants had significantly greater cover in the treated watershed, including the legume Lotus wrightii. Our results suggest that the increased herbaceous cover resulting from an ORSM treatment of a single watershed induced a positive, initial response by butterflies. Using butterflies as indicators of site productivity and species richness, our results suggest ORSM is a promising technique for restoring biodiversity in degraded piñon‐juniper woodlands.     

Traditional management of forests: plant and bird community responses to alternative restoration of oak–hazel woodland in Sweden

Species richness of vascular plants and birds were examined in relation to five types of management (including abandonment) of oak-hazel woodland in south-central Sweden. The biodiversity of this type of woodland is affected by lengthy management in contrast to present emphasis on the fragmentation of more or less pristine forests. The woodlands derive from old deciduous forests but were a source of agricultural commodities from medieval time to end of the 19th century. Vascular plants and birds were censused during spring–summer for four years. Total number of plant species, species of field layer forbs, breeding birds and migrant birds were more numerous at simulated original management with mowing of small interior grasslands than at mechanical clearing or abandonment. Summer grazing led to intermediate numbers. Exotic plants were more common at long-time abandonment. Species richness of trees and shrubs, graminoids, all spring birds, resident birds and non-passerine birds did not exhibit any difference between treatments. Inter-site variation in species richness was usually smaller at abandonment than at true management. Species richness of plants and birds showed positive correlation in the particularly large sites examined. The general findings were in accordance with the intermediate disturbance hypothesis. Original management would secure most potential plant and bird species but extensive cattle grazing would also retain many species.     

Structure and Reactivity of a Biological Soil Crust from a Xeric Sandy Soil in Central Europe

The investigation was designed to explore the structure, composition, and activity of a biological soil crust on an acidic, sandy soil from a temperate climate. The crust covers several hundreds of square meters on the hilltop of a large terminal moraine. The conjugate alga Zygogonium ericetorum forms the essential matrix for the crust, a dense web of algal filaments with interspersed lichens and mosses. The crust is composed of three layers, with an uppermost layer consisting nearly entirely of a dense algal mat. In lower layers, a parasitic fungus, penetrating the algal cells, is another important component of the crust community. In this soil crust, photosynthetic and respiratory activity is stabilized at low water activities.     

Patterns of Rodent Species Diversity and Abundance in a Kenyan Relict Tropical Rainforest

Patterns of rodent species abundance and diversity were examined over a 5 months period in two areas of a Kenyan relict tropical rainforest. The two areas are subjected to different administrations which lead to various levels of anthropogenic disturbance: one can be considered relatively disturbed and one relatively undisturbed. Anthropogenic disturbance causes a reduction in woody stem density between 0 and 1.5 m and reduced understory tree canopy cover. Rodent abundance was estimated using the program CAPTURE and compared with the number of individuals actually captured. Density was estimated with three different methods, two of these utilised a boundary strip to estimate effective size of the area trapped. Density resulted in being relatively high in both areas, so population might have been at a peak. Species richness was higher in the disturbed forest, while species diversity and evenness was higher in the undisturbed forest. We suggest that in the disturbed forest the increase in number of species might be due to sporadical entrance in the forest by non-forest species, while the decrease in diversity might be due to the decrease of lower strata vegetation that occurs in the disturbed forest, hence this factor might affect species equitability. Bibliographic data supports this hypothesis as rodent species diversity and ground vegetation cover have been found to be correlated.     

The Chironomid Communities of Woodland Springs and Spring Brooks, Severely Endangered and Impacted Ecosystems in a Lowland Region of Eastern Germany (Diptera: Chironomidae)

The distribution of chironomid species from four springs and twelve spring brooks in a region heavily affected by industrial activity in eastern Germany was studied. The aims were (1) to document the chironomid taxa communities at the species level, as far as possible, and the most important environmental factors of representative springs and spring brooks of the region, (2) to analyse the distribution of the ecological groups within these small ecosystems and (3) to emphasize the importance of the protection of spring areas and spring brooks in this woodland area shown by the chironomid fauna. There was high degree of abiotic variation among the water bodies, with pH ranging from 2.79 to 6.89. While diversity did not correlate with pH nor with conductivity, significant differences existed between the spring mouth and the reaches some metres downstream with respect to several abiotic parameters and the distribution of the chironomids: oxygen concentrations and taxonomic diversities were higher in spring brooks (2.18–8.98mgO₂/l; 5–28 taxa) than in the spring areas (0.13–2.95mgO₂/l; 0–7 taxa). A total of 74 chironomid taxa were recorded. The chironomid communities are characterized by the presence of rheophilic, cold-stenothermic, crenophilic and sometimes tyrphophilic elements in each site. The data show that each of the spring–spring brook systems surveyed is unique both in biotic and abiotic respects. As the spring system is sensitive to changes in landscape functions (e.g. groundwater levels), the fauna can serve as an indicator of landscape health. Therefore, these small ecosystems should be conserved as a reference.     

Patterns of Below- and Aboveground Biomass in Eucalyptus populnea Woodland Communities of Northeast Australia along a Rainfall Gradient

In vegetated terrestrial ecosystems, carbon in below- and aboveground biomass (BGB, AGB) often constitutes a significant component of total-ecosystem carbon stock. Because carbon in the BGB is difficult to measure, it is often estimated using BGB to AGB ratios. However, this ratio can change markedly along resource gradients, such as water availability, which can lead to substantial errors in BGB estimates. In this study, BGB and AGB sampling was carried out in Eucalyptus populnea-dominated woodland communities of northeast Australia to examine patterns of BGB to AGB ratio and vertical root distribution at three sites along a rainfall gradient (367, 602, and 1,101 mm). At each site, a vegetation inventory was undertaken on five transects (100 × 4 m), and trees representing the E. populnea vegetation structure were harvested and excavated to measure aboveground and coarse-root (diameter of at least 15 mm) biomass. Biomass of fine and small roots (diameter less than 15 mm) at each site was estimated from 40 cores sampled to 1 m depth. The BGB to AGB ratio of E. populnea-dominated woodland plant communities declined from 0.58 at the xeric end to 0.36 at the mesic end of the rainfall gradient. This was due to a marked decline in AGB with increased aridity whereas the BGB was relatively stable. The vertical distribution of fine roots in the top 1 m of soil varied along the rainfall gradient. The mesic sites had more fine-root biomass (FRB) in the upper soil profile and less at depth than the xeric site. Accordingly, at the xeric site, a much larger proportion of FRB was found at depth compared to the mesic sites. The vertical distribution patterns of small roots of the E. populnea woodland plant communities were consistently )-shaped, with the highest biomass occurring at 15–30-cm depth. The potential significance of such a rooting pattern for grass–tree and shrub–tree co-existence in these ecosystems is discussed. Overall, our results revealed marked changes in BGB to AGB ratio of E. populnea woodland communities along a rainfall gradient. Because E. populnea woodlands cover a large area (96 M ha), their contribution to continental-scale carbon sequestration and greenhouse gas emission can be substantial. Use of the rainfall-zone-specific ratios found in this study, in lieu of a single generic ratio for the entire region, will significantly improve estimates of BGB carbon stocks in these woodlands. In the absence of more specific data, our results will also be relevant in other regions with similar vegetation and rainfall gradients (that is, arid and semiarid woodland ecosystems).     

Seasonal Variability in Abundance and Diversity of Soil Gymnamoebae Along a Short Transect in Southeastern USA

The abundance and diversity of gymnamoebae in three subsoils varying in compaction and water retention along a 1.2 m transect were documented as the local climatic conditions changed from late summer 1999 through mid-summer 2000. The mean density of gymnamoebae for the loose soil (1,655/g) was greater than either the most compact (1,468/g) or moderately compact soil (851/g). Minimum densities occurred in middle and late summer for all soils while significant (F = 38.803, < or = 0.0002) density peaks at 3.212/g occurred in early summer in the most compact soil, 2.928/g in the least compact, and 2,209/g in the moderately compact soil. Limax non-eruptive gymnamoebae (mt 2) correlated (r = 0.49, p < or = 0.016) with moisture while eruptive limax gymnamoebae ( 3) correlated with temperature (r = 0.07, p < or = 0.024), moisture (r = 0.58, p < or = 0.001) and precipitation (r = 0.46, p < or = 0.029). Flattened or discoid amoebae (mt 4) dominated throughout most of the survey, and the two limax groups showed inverse relationships. Chi-square analyses showed significant differences in the numbers of limax eruptive gymnamoebae compared to all other morphotypes on all but one sampling period.     

Diversity and Abundance of Litter Frogs in a Montane Forest of Southeastern Brazil: Seasonal and Altitudinal Changes1

We sampled litter frogs in an 1800-ha mid-elevation seasonal forest in southeastern Brazil. One hundred 8 * 8-m plots were sampled during the dry/cold season and wet/warm season (unburned areas); we also examined the effects of fire in recently burned areas. A total of 267 frogs (305 g), belonging to 16 species (4 families) were caught. A single species comprised 78.5 percent of the individuals in the dry/cold season and 54.3 percent in the wet/warm season. The density of individuals did not change significantly with season, biomass did. Density and biomass of frogs were positively correlated with altitude. A Mantel test indicated that biological data (species and their abundance) were significantly associated with environmental parameters. The burned areas showed low values in richness, density and biomass of frogs. Harsh seasonal climate and a history of human disturbance may produce the low observed diversity values. The greater densities of frogs in sites of higher elevation may primarily result from mist-generated humidity, which diminishes the harshness of the dry/cold season in relation to lower sites.     

Response of ant and terrestrial spider assemblages to pastoral and military land use,and to landscape position,in a tropical savanna woodland in northern Australia

This study aims primarily to assess the response of two invertebrate groups to the effects of pastoralism and military training, at one site in the tropical savanna of north‐eastern Queensland. The richness and species composition of ants and terrestrial spiders were examined at two contrasting times of year across three land use treatments (pastoralism, military training and undisturbed) and four landscape positions (upper slope to riparian). Ant species richness was least in the grazed sites, and a high proportion of the ant species recorded varied significantly in frequency between the grazed and the two ungrazed land uses. This variation was generally greater than that associated with landscape position. Although variation in the richness of spiders was significantly related to land‐use type, this effect was less pronounced than for ants, was less marked than variation associated with landscape position and was confounded by a strong interaction between land use and landscape position. Quadrat‐scale variation in the composition of spider assemblages was influenced most by season of sampling. For both spiders and ants, there were few differences in richness or species composition between undisturbed land and that managed for military use.     

Formation of Aerenchyma and the Processes of Plant Ventilation in Relation to Soil Flooding and Submergence

Abstract: Enhanced development of gas-spaces beyond that due to the partial cell separation normally found in ground parenchymas and their derivatives creates tissue commonly termed "aerenchyma". Aerenchyma can substantially reduce internal impedance to transport of oxygen, nitrogen and various metabolically generated gases such as carbon dioxide and ethylene, especially between roots and shoots. Such transport lessens the risk of asphyxiation under soil flooding or more complete plant submergence, and promotes radial oxygen loss from roots leading to oxidative detoxification of the rhizo-sphere. Aerenchyma can also increase methane loss from waterlogged sediments via plants to the atmosphere. This review of the formation and functioning of aerenchyma particularly emphasises research findings since 1992 and highlights prospects for the future. Regarding formation, attention is drawn to how little is known of the regulation and processes that create schizogenous aerenchyma with its complex cell arrangements and differential cell to cell adhesion. More progress has been made in understanding lysigenous aerenchyma development. The review highlights recent work on the processes that sense oxygen deficiency and ethylene signals, subsequent transduction processes which initiate cell death, and steps in protoplast and wall degeneration that create the intercellular voids. Similarities between the programmed cell death and its causes in animals and the predictable patterns of cell death that create lysigenous aerenchyma are explored. Recent findings concerning function are addressed in terms of the diffusion aeration of roots, rhizosphere oxygenation and sediment biogeochemistry, photosynthesis and ventilation, pressurised gas-flows and greenhouse gas emissions and aspects of ventilation related to secondary thickening.     

Restoring Kangaroo Grass (Themeda triandra) to grassland and woodland understoreys: a review of establishment requirements and restoration exercises in south-east Australia

Summary Temperate grassy ecosystems are amongst Australia's most endangered ecosystems. Most remnants are small, fragmented and highly degraded. Practical methods for restoring native understorey species are urgently required. Dominant native grasses such as Kangaroo Grass (Themeda triandra Forssk.) and Tussock‐grasses (Poa species) have been eliminated from many remnants by heavy grazing in the past. The reintroduction of these grasses is a critical step for understorey restoration. This paper (i) reviews the literature on Themeda seed biology and seedling establishment; (ii) summarizes the lessons learnt from three major attempts to establish Themeda stands in south‐east Australia; and (iii) identifies the research needed to enhance Themeda restoration. Considerable information is available on Themeda seed and establishment biology, and restoration exercises have shown that Themeda stands can be readily established by surface‐spreading awned seeds in seed‐bearing hay. However, many practical challenges remain, including the need to identify optimal sowing periods, create better seedbed conditions, develop practical mulching techniques, and improve weed control. The use of seed‐bearing hay has constrained restoration to relatively small areas in the past. Future trials may benefit by using more concentrated seed products such as seed‐bearing florets and pure seeds which permit larger areas to be restored at one time.     

Impact of Ectomycorrhizosphere on the Functional Diversity of Soil Bacterial and Fungal Communities from a Forest Stand in Relation to Nutrient Mobilization Processes

The ectomycorrhizal symbiosis alters the physicochemical and biological conditions in the surrounding soil, thus creating a particular environment called ectomycorrhizosphere, which selects microbial communities suspected to play a role in gross production and nutrient cycling. To assess the ectomycorrhizosphere effect on the structure of microbial communities potentially involved in the mobilization of nutrients from the soil minerals in a poor-nutrient environment, we compared the functional diversity of soil and ectomycorrhizosphere bacterial communities in a forest stand. Two hundred and sixty-four bacterial strains and 107 fungal strains were isolated from the bulk soil of an oak (Quercus petraea) stand and from oak–Scleroderma citrinum ectomycorrhizosphere and ectomycorrhizae, in two soil organo-mineral horizons (0 to 3 cm and 5 to 10 cm). They were characterized using two in vitro tests related to their capacities to mobilize iron and phosphorus. We demonstrated that the oak–S. citrinum ectomycorrhizosphere significantly structures the culturable bacterial communities in the two soil horizons by selecting very efficient strains for phosphorus and iron mobilization. This effect was also observed on the diversity of the phosphate-solubilizing fungal communities in the lower soil horizon. A previous study already demonstrated that Laccaria bicolor–Douglas fir ectomycorrhizosphere structures the functional diversity of Pseudomonas fluorescens population in a forest nursery soil. Comparing to it, our work highlights the consistency of the mycorrhizosphere effect on the functional diversity of bacterial and fungal communities in relation to the mineral weathering process, no matter the fungal symbiont, the age and species of the host tree, or the environment (nursery vs forest). We also demonstrated that the intensity of phosphorus and iron mobilization by the ectomycorrhizosphere bacteria isolated from the lower soil horizon was significantly higher compared to that which was isolated from the upper horizon. This reveals for the first time a stratification of the functional diversity of the culturable soil bacterial communities as related to phosphorus and iron mobilization.     

Abundance and Distribution of Native and Alien Grasses in a “Cerrado” (Brazilian Savanna) Biological Reserve1

Several species of African grasses brought to Brazil as cattle forage have spread widely, outcompeting native herb species. The open forms of Brazilian savanna (“campo cerrado” and “campo sujo”) are the most affected by such invasions, because their structure is open, permitting enough sunlight into the lower strata. The invasion of alien forage grasses occurs in almost every cerrado nature reserve. This study was carried out in the “Cerrado de Hmas Biological Reserve”, Pirassununga, São Paulo State, Brazil, with the following objectives: (a) to compare the abundance of native and alien grass species; (b) to verify the importance of such alien grasses in the community; (c) to identity distribution patterns for the alien grass species in a gradient from the edge (highly disturbed) to the center (less disturbed) of the reserve; and (d) to explore the distribution of native and alien grasses in the search for possible competitive interactions. Using the “point method,” a total of 260 points was sampled and 52 species were recorded. The four most frequent species (FA = absolute frequency) were two native (Echinolaena inflexa [Poir.J Chase [FA = 38.85%] and Diandrostachya chrysotrix [Nees] Jacues Felix [FA = 15.38%]) and two alien African species (Melinis minutiflora Beauv. [FA = 33.08%] and Brachiaria decumbens Stapf [FA = 13.85%]). M. minutiflora and E. inflexa had higher values of absolute vigor (67.69 and 59.62%, respectively), relative vigor (28.16 and 24.80%, respectively), and cover (100.77 and 98.47, respectively), indicating higher biomasses and densities and their dominance in the community. B. decumbens presented the highest number of contacts per point, showing the highest stratification. To detect possible edge–center distribution gradients, correspondence analysis was done, initially using all the recorded species and subsequently only the four more frequent grasses, with similar results: (a) the alien grasses, especially M. minutiflora, did not show a distinct distribution gradient from edge to center, but occurred over the whole reserve; (b) no distinct ecotonal band around the reserve (edge–belt) was detected, the whole reserve seeming to be “ecotonal”; and (c) E. inflexa and M. minutiflora showed similar phytosociological patterns, and spatial distribution; association between these two species was statistically significant.     

Development and Application of a Predictive Model of Freshwater Fish Assemblage Composition to Evaluate River Health in Eastern Australia

Multivariate predictive models are widely used tools for assessment of aquatic ecosystem health and models have been successfully developed for the prediction and assessment of aquatic macroinvertebrates, diatoms, local stream habitat features and fish. We evaluated the ability of a modelling method based on the River InVertebrate Prediction and Classification System (RIVPACS) to accurately predict freshwater fish assemblage composition and assess aquatic ecosystem health in rivers and streams of south-eastern Queensland, Australia. The predictive model was developed, validated and tested in a region of comparatively high environmental variability due to the unpredictable nature of rainfall and river discharge. The model was concluded to provide sufficiently accurate and precise predictions of species composition and was sensitive enough to distinguish test sites impacted by several common types of human disturbance (particularly impacts associated with catchment land use and associated local riparian, in-stream habitat and water quality degradation). The total number of fish species available for prediction was low in comparison to similar applications of multivariate predictive models based on other indicator groups, yet the accuracy and precision of our model was comparable to outcomes from such studies. In addition, our model developed for sites sampled on one occasion and in one season only (winter), was able to accurately predict fish assemblage composition at sites sampled during other seasons and years, provided that they were not subject to unusually extreme environmental conditions (e.g. extended periods of low flow that restricted fish movement or resulted in habitat desiccation and local fish extinctions).     

Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest,Northern Territory,Australia

Abstract This opportunistic study compares the vegetation, fuel loads and vertebrate fauna of part of a 120‐ha block of tropical open forest protected from fire for 23 years, and an adjacent block burnt annually over this period. Total fuel loads did not differ significantly between the unburnt and annually burnt sites, but their composition was markedly different, with far less grassy fuel, but far more litter fuel, in the unburnt block. There were major differences between treatments in the composition of trees and shrubs, manifest particularly in the number of stems. There was no overall difference in plant species richness between the two treatments, but richness of woody species was far higher in the unburnt treatment, and of annual and perennial grasses, and perennial herbs in the annually burnt treatment. Change in plant species composition from annually burnt to unburnt treatment was directional, in that there was a far higher representation of rainforest‐associated species (with the percentage of woody stems attributable to ‘rainforest’ species increasing from 24% of all species in the annually burnt treatment to 43% in the unburnt treatment, that of basal area from 9% to 30%, that of species richness from 8% to 17%, and that of cover from 12 to 47%). The vertebrate species composition varied significantly between treatments, but there was relatively little difference in species richness (other than for a slightly richer reptile fauna in the unburnt treatment). Again, there was a tendency for species that were more common in the unburnt treatment to be rainforest‐associated species. The results from this study suggest that there is a sizeable and distinct set of species that are associated with relatively long‐unburnt environments, and hence that are strongly disadvantaged under contemporary fire regimes. We suggest that such species need to be better accommodated by fire management through strategic reductions in the frequency of burning.     

Functional Diversity of Culturable Bacterial Communities in the Rhizosphere in Relation to Fine-root and Soil Parameters in Alder Stands on Forest, Abandoned Agricultural, and Oil-shale Mining Areas

Grey alder (Alnus incana) and black alder (Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil-shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil–root interface and in the bulk soil in relation to fine-root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community-level physiological profiles (CLPP) of culturable bacteria in soil–root interface and bulk soil samples. CLPP were summarized as AWCD (average well color development, OD 48 h⁻¹) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil–root interface. The soil–root interface/bulk soil ratio of AWCD was estimated. Substrate-induced respiration (SIR) and basal respiration (BAS) of bulk soil samples were measured and metabolic quotient (Q = BAS/SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g⁻¹ and from 0.12 to 0.51, respectively. Short-root morphological studies were carried out by WinRHIZO^TM Pro 2003b; mean specific root area (SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m² kg⁻¹, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil–root interface and bulk soil were found for the young alder stands on oil-shale mining spoil and on abandoned agricultural land. Soil–root interface/bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency (FOE) was negatively correlated with soil–root interface/bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short-root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder-species-related differences were revealed.     

我国入侵植物多样性的区域分异及其影响因素——以74个地区数据为基础

以我国74个地理单位282种外来入侵植物的分布和环境数据为基础,应用除趋势对应分析、典范对应分析和回归分析方法,探讨了我国境内入侵植物区系组成、地理分布格局及其影响因素。主要结果如下:(1)我国74个地区共有282种外来入侵种,出现频率相对较高的外来入侵种是小飞蓬(Conyza canadensis)、刺苋(Amaranthus spinosus)、一年蓬(Erigeron annuus)、空心莲子草(Alternathera philoxeroides)、土荆芥(Chenopodium ambrosioides)、圆叶牵牛(Pharbitis purpurea)、曼陀罗(Datura stramonium)、皱果苋(Amaranthus viridis)、裂叶牵牛(Pharbitis nil)、反枝苋(Amaranthus retroflexus)、三叶鬼针草(Bidens pilosa)、凤眼莲(Eichhornia crassipes)等;(2)菊科(Compositae,67,种数)、禾本科(Gramineae,32)、豆科(Leguminosae,29)、苋科(Amaranthaceae,23)、旋花科(Convolvulaceae,13)是我国境内含入侵种最丰富的5个科,共计有164种,占我国入侵植物总数的58.16%;(3)我国外来入侵植物主要源自于热带美洲、北美洲、欧洲、地中海-西亚和中亚、非洲和南亚;(4)外来入侵植物多样性在我国的区域分异明显,热带-南亚热带、中(北)亚热带和温带三大区域的入侵种组成有较大差异:马缨丹(Lantana camara)、含羞草(Mimosapudica)、胜红蓟(Ageratum conyzoides)、刺苋、小飞蓬、飞扬草(Euphorbia hirta)、五爪金龙(Ipomoea cairica)、空心莲子草、三叶鬼针草和金腰箭(Synedrella nodiflora)是热带-南亚热带区域中出现频率最高的前10种入侵植物;中亚热带和北亚热带区域出现频率最高的入侵种分别是一年蓬、小飞蓬、刺苋、土荆芥、北美独行菜(Lepidium virginicum)、美洲商陆(Phytolacca americana)、牛筋草(Eleusine indica)、紫茉莉(Mirabilis jalapa)、空心莲子草和三叶鬼针草;温带区域出现频率最高的是反枝苋、小飞蓬、圆叶牵牛、一年蓬、野西瓜苗(Hibiscus trionum)、杂配藜(Chenopodium hybridum)、苦苣菜(Sonchus oleraceus)、野燕麦(Avena fatua)、曼陀罗和皱果苋;(5)年降雨量、年均温度、年极端低温、无霜期和年均积温是影响我国外来入侵种空间分布格局的主要气象因素,年极端高温和年日照时数的影响相对较小;人口密度和交通密度对入侵种的地理分布也均有很大的影响;(6)随着年均温度、无霜期、人口密度、交通密度、年极端低温、年均降雨量和年积温的增加,外来入侵植物的种数呈线性增加,随着纬度的增加,种数则呈线性递减,种数与这8个环境因素间的关系达到极显著的水平;(7)不同地理来源的外来入侵种在我国的分布主要受纬度、年降雨量、年均无霜期、年均温度、交通密度、年极端低温和年均积温的影响。由于外来入侵种在我国分布呈现明显的区域分化,因此,应用建立具有区域特点的外来植物入侵风险评估系统。     

Helicobacter pylori CagA: Analysis of Sequence Diversity in Relation to Phosphorylation Motifs and Implications for the Role of CagA as a Virulence Factor

CagA is transported into host target cells and subsequently phosphorylated. Clearly this is a mechanism by which Helicobacter pylori could take control of one or more host cell signal transduction pathways. Presumably the end result of this interaction favors survival of H. pylori, irrespective of eventual damage to the host cell. CagA is noted for its amino acid (AA) sequence diversity, both within and outside the variable region of the molecule. The primary purpose of this review is to examine how variation in the type and number of CagA phosphorylation sites might determine the outcome of infection by different strains of H. pylori. The answer to this question could help to explain the widely disparate results obtained when H. pylori CagA status has been compared to type and severity of disease outcome in different populations, that is in different countries. Analysis of all available CagA sequences revealed that CagA contains both tyrosine phosphorylation motifs (TPMs) and cyclic-AMP-dependent phosphorylation motifs (CPMs). There are two potential CPMs near the N-terminus of CagA and at least two in the repeat region; these are not all equally well conserved. We also defined a 48-residue AA sequence, which includes the N-terminal TPM at tyrosine (Y)-122, which distinguishes between Eastern (Hong Kong-Taiwan-Japan-Thailand) H. pylori isolates and those from the West (Europe-Africa-the Americas-Australia). All 28 of the Eastern type CagA proteins have a functional N-terminal TPM whereas 11 of 47 (23.4%) of the Western type contain an inactive motif, with threonine (T) replacing the critical aspartic acid (D) residue. Only 13 of 24 (54%) known CagA sequences have an active TPM in the repeat region and only one has two TPMs in this region. The potential TPM near the C-terminus of CagA is not likely to be important since only 3 of 24 (12.5%) sequences were found to be intact. Protein database searches revealed that the AA sequence immediately following the TPM at Y-122 in CagA is homologous with a pair of PDZ domains which are common in signal transducing proteins, particularly tyrosine phosphatases. This provides a theoretical link between CagA and many of the observed responses of host cells to H. pylori. In summary, not all CagA proteins are equal in their potential for initiating host cell responses via signal transduction pathways. The degree of functional diversity of this protein depends upon which phosphorylation motifs are critical to the biological activity of CagA.