Litter and its interaction with standing vegetation affect seedling recruitment in Tibetan alpine grasslands

Background: Seedling recruitment is widely recognised to be important in the maintenance of diversity and coexistence of species. It is not clear how local abiotic factors mediated by litter and biotic interactions influence plant species recruitment in alpine grasslands.

Aims: To determine how litter and standing vegetation affected seedling recruitment in plant communities in Tibetan alpine grasslands.

Methods: Seedling recruitment was quantified in response to experimental treatments: (1) removal of standing vegetation and litter; (2) removal of standing vegetation with litter intact; (3) intact standing vegetation and removal of litter and (4) control: intact standing vegetation and litter.

Results: Litter removal increased seedling numbers, while standing vegetation removal had no effect. An interaction between litter and standing vegetation removal marginally increased seedling number. Species richness of seedlings was not related to either litter removal or standing vegetation removal. Species composition of seedling differed significantly between removal of both litter and standing vegetation and control.

Conclusions: Litter and its interaction with standing vegetation has an important role in affecting plant species recruitment in this alpine plant community. In contrast, biotic interactions, such as competition or facilitation from standing vegetation, appear to have only minor effects on recruitment.     

Effects of phytoremediation and application of organic amendment on the mobility of heavy metals in a polluted soil profile

This research aims to assess the effect of the application of biosolids compost and phytoremediation on the mobility of total and biodisponibles (DTPA) fractions of cadmium, copper, lead, and zinc from different horizons of a superficially contaminated soil. Leaching experiment in soil columns was proposed. Treatments contemplated application of compost biosolid and phytoremediation. Two destructive samplings were performed. Total and DTPA trace metals were identified in each horizon. The overall performance of the various elements in its total and DTPA forms show greater concentration in horizon A and fewer gradients between horizons Bt and BC, thus assuming that the high content of clay in horizon Bt (62.9%) limits its movement through the horizons. In the mobile nutrients, a greater mobility was evidenced in DTPA fractions if compared to Total fractions. In the horizon A, the more mobile metals, such as Zn and Cd, evidenced a greater percentage of DTPA/Total fractions in all treatments. The application of compost with or without plant diminished the mobilization of Zn, Cu, and Cd Total, thus limiting a potential leaching to inferior horizons. However, this effect was not observed in the DTPA fraction.     

Growth and mineral element composition in two ecotypes of Thlaspi caerulescens on Cd contaminated soil

The heavy metal hyperaccumulator Thlaspi caerulescens occurs both on heavy metal polluted soils (metallicolous ecotype MET) and on soils with normal heavy metal content (non-metallicolous ecotype: NMET). In order to assess the extent and structure of variation in growth, shoot accumulation of Cd, Zn and mineral element (Ca, Mg, K, Fe), a MET ecotype from Belgium and a NMET ecotype from Luxembourg were studied. Seven maternal families from two populations of each ecotype were grown on both Cd and Zn contaminated soil. Although both ecotypes presented a similar heavy metal tolerance in the experimental conditions tested, they differed in several points. The MET populations had markedly higher biomass and higher root:shoot ratio compared to NMET populations. The Zn, and at lesser extent, the Cd hyperaccumulation capacity tended to be higher in the NMET populations. The same trend was observed for the foliar concentrations of Mg, Ca and Fe with NMET populations having higher concentrations compared to MET ones. Cd and Zn concentrations were negatively correlated with the biomass of both ecotype. However, the negative correlation between the Zn and biomass was much lower in MET ecotype suggesting a tighter control of internal Zn concentration in this ecotype. Finally, although the Cd phytoextraction capacity was similar in both ecotype, a higher Zn phytoextraction capacity was detected in NMET ecotype when these plants grow on moderate Cd and Zn concentrations.     

The potential of some soil amendments to improve tree growth on metalliferous mine wastes

Trees are commonly planted on metalliferous mine wastes as a means of reclaiming these contaminated substrates. Other land-uses are often limited. However tree establishment is often poor owing to hostile substrate properties such as acidity, low macronutrient concentrations, high trace element concentrations, poor substrate structure and poor water retention. Soil amendments are a potentially cheap amelioration option. A factorial experiment was set-up to investigate the effects of seven amendments on the substrate chemistry and the growth and leaf chemistries of alder and sycamore. The amendments included ammonium nitrate, mineral phosphate and sulphate of potash fertilizers, calcareous sand, a superexpanding polyacrylamide gel polymer, cake sewage sludge and diatomite. The last two amendments are used here in a novel capacity. The most successful amendments with regard to their growth and leaf chemistry effects were found to be cake sludge and diatomite for alder and mineral phosphate, calcareous sand and cake sludge for sycamore. The least successful amendments were ammonium nitrate, sulphate of potash and calcareous sand for alder and ammonium nitrate for sycamore. The results differed according to the autoecological properties of the two species, with alder being easily the most productive. The implications of these results for tree-planting schemes are discussed.     

重金属Cd、Zn、Cu、Pb对土壤微生物和酶活性的影响

采用室内培养实验(25℃),研究了不同培养时间下重金属Cd、Zn、Cu、Pb(浓度分别为50,800,400,800mg.kg-1)污染对土壤微生物和酶活性的影响。结果表明,土壤蔗糖酶、过氧化氢酶和脱氢酶活性随着培养时间的增加而显著下降,在培养20d的时候达到最小值,然后酶活性缓慢升高。Cu对脲酶活性以及Cd对酸性磷酸酶和脲酶活性的抑制作用随时间增加而增加。土壤微生物生物量碳、细菌、真菌和放线菌数量随培养时间的增加均表现出先降低后升高的变化趋势。Cd和Cu对微生物生物量氮的抑制作用则随着培养时间的增加而增强,在培养30d时微生物生物量氮到达最低值,分别较培养10天减少了12.6%和16.5%。     

Effects of grass-encroachment on vegetation and soil in Dutch dry dune grasslands

The encroachment of tall grass species in open dune vegetation, as observed in the Dutch dry dune area, is considered unfavourable for nature conservation. The effects of grass-encroachment on the vegetation and the availability of light and its relation to nutrients were investigated through a comparative study of grass-dominated and open dune grassland plots at ten locations along the Dutch coast.Grass-dominated plots have a low species diversity and number of species, especially of mosses and lichens. This is associated with a high biomass and a low availability of light at soil surface. In addition, nutrient availability seems to be important. Root biomass and the amounts of both ectorganic and endorganic matter are significantly higher in grass-dominated plots, which may account for the higher nutrient uptake in the vegetation.It is likely that a grass-dominated system can maintain and consolidate itself because of the better competition for light and nutrients. The relevance of these results for restoration management is briefly discussed.     

Pigment characterisation of suspended matter in association with particulate heavy metal loadings in the German Bight and Elbe Estuary

The pigment fingerprints, determined by HPLC, of suspended matter from different areas of the German Bight and from the Elbe Estuary are presented. These include areas with suspended matter concentrations varying between 10 mg l^–1 in the deeper waters in the middle of the Bight and 150 mg l^–1 in the Elbe mouth. Pigment data allows the identification of three groups of suspended matter (marine, turbidity zone and Elbe) for the numerous different locations. The changes in pigment concentrations in the suspended matter over tidal cycles are considered. The presence of pigments and pigment breakdown productsi.e. lutein and chlorophyllides is used to assess the possible condition of the phytoplankton present in the suspended matter. These pigment characteristics are compared with the loading of the heavy metals cadmium, copper, manganese, iron, zinc and lead in the particulate matter. It has been demonstrated that the pigments of the planktonic material can be used very effectively to identify different types of suspended matter and that the heavy metal loadings of the suspended matter were significantly correlated with chlorophyll-a.     

Effect of Cd,Zn, and Pb Compound Pollution on Celery in a Ferric Acrisol

A pot experiment with an orthogonal experimental design L₉(3⁴) was conducted to study the combined effects of Cd, Zn, and Pb on the growth and metal content of celery grown in a ferric acrisol. The uptake of Cd, Zn, and Pb by celery was not only affected by the individual elements, but also by combinations of the elements. The effect of coexisting elements on plant uptake of the heavy metals depended on the concentration ratios of the elements. There is a given ratio where a maximum antagonism or synergism effect occurs. The combinations of elements clearly affected the dry weight of celery and the heavy metal concentration in celery. The removal rate (the ratio of plant total uptake to the total metal content in soil) was in the order of Cd > Zn > Pb, with no obvious difference between the removal rate under single pollution and that under compound pollution.     

Distribution of Toxic Trace Metals Zn,Cd, Pb,and Cu in Tirupati Soils,India

The concentrations of toxic trace metals in the soil samples collected from Tirupati, India, have been determined using differential pulse anodic stripping voltammetry (DPASV). The total metal concentrations of the soils in the study area were in the following ranges: 19.5 to 23.6 mg of Zn, 0.032 to 0.036 mg of Cd, 15.8 to 18.9 mg of Pb, and 19.0 to 23.4 mg of Cu per kg soil. Analysis of standard reference material IAEA-SOIL-5 indicates good accuracy. Recoveries were nearly quantitative for all elements studied. Comparison of the average metal concentration levels with world averages indicates an elevated value for Pb. The applicability of this method was crosschecked with AAS and the results were in good agreement.     

电感耦合等离子质谱法(ICP-MS)法测定茵栀黄注射液中有害元素铅、砷、镉、汞、铜的含量

建立了电感耦合等离子体质谱法(ICP-MS)测定茵栀黄注射液中Pb、As、Cd、Hg、Cu 5种元素的方法。样品经微波消解后,直接用ICP-MS同时测定上述5种元素,结果5种元素的检出限分别在5～1250 ng/L之间;线性良好,线性相关系数均为r≥0.999;精密度RSD3.5%;回收率在95.7%～107.5%之间。方法操作简便、分析速度快、灵敏度高,各项分析性能指标均达到要求,适用于茵栀黄注射液中有害元素的测定。     

Intertidal distribution and species composition of brachyuran crabs at two rocky shores in Central Portugal

The objectives of the present study are to describe and compare the brachyuran community of rocky shores within the Central Portuguese coast and to examine the zonation patterns of the most representative species. For this, randomly placed transects were surveyed to obtain crab counts according to microhabitat and intertidal level. Repeated sampling in two different shores during two different seasons provided spatial and temporal replication for zonation analyses. Seven species were registered: Pachygrapsus marmoratus, Eriphia verrucosa, Xantho incisus, Carcinus maenas, Necora puber, Pirimela denticulata and Pilumnus hirtellus. Species density rankings are the same at both localities, but the less exposed shore presents higher diversity. While most species are mainly confined to specific microhabitats in the lower level, P. marmoratus and E. verrucosa can exploit the whole intertidal range. Regardless of shore and season, E. verrucosa is more abundant in the lower intertidal levels, while no such zonation patterns were recorded for P. marmoratus. Initial predictions concerning the effect of wave exposure and temperature on the zonation of those species are not validated after analysing the factorial model proposed. Between-shore contrasts were found instead, with higher densities recorded in the more exposed locality for both species. Possible causes of the observed patterns are discussed.     

Establishment and persistence of target species in newly created calcareous grasslands on former arable fields

The effects of different restoration measures and management variants on the vegetation development of newly created calcareous grasslands were studied in southern Germany from 1993 to 2002. In 1993, fresh seed-containing hay from a nature reserve with ancient calcareous grasslands was transferred onto ex-arable fields with and without topsoil removal. Nine years after start of the restoration, the standing crop was lower and the cover of bare soil was higher on topsoil-removal sites than on sites without soil removal. Topsoil removal had a positive effect on the proportion of target species (class Festuco-Brometea), because the number and cover of productive meadow species (class Molinio-Arrhenatheretea) were reduced. Persistence of hay-transfer species and the number of newly colonizing target species were highest on topsoil-removal sites. On plots with and without soil removal, species richness and the number of target species increased quickly after hay transfer and were always higher on hay-transfer plots than on plots that had not received hay in 1993. In 2002, differences induced by hay transfer were still much more pronounced than differences between management regimes. Management by mowing, however, led to higher species richness, a greater number of target species and a lower number of ruderals in comparison to no management on restoration fields without soil removal. A detrended correspondence analysis (DCA) indicated that vegetation composition of the hay-transfer plots of the restoration fields still differed from the vegetation of ancient grasslands in the nature reserve. Vegetation of an ex-arable field in the nature reserve (last ploughed in 1959) showed an intermediate successional stage. In general our results indicate that the transfer of autochthonous hay is an efficient method for the restoration of species-rich vegetation, which allows not only quick establishment but also long-term persistence of target species.     

Avifaunal gradients in two arid zones of central Iran in relation to vegetation, climate, and topography

Aim To identify the ecological factors (related to vegetation, altitude, climate, or geomorphology) that could explain the main gradients of avifaunal richness and composition in arid environments of Central Iran. Location The study was carried out in two nearby semi‐arid protected areas of the Ispahan province: the Kolah‐Ghazi National Park (c. 50,000 ha; 1540–2535 m a.s.l.) and the Mouteh Wildlife Refuge (c. 220,000 ha; 1493–2900 m a.s.l.). Annual average precipitation and temperature range from 155–205 mm and 15–19.5 °C, respectively. Vegetation cover is sparse. Methods The two study areas were sampled with a 1 × 1 km grid design. A subset of 405 squares was randomly chosen and each was visited once during spring or summer by a team of five observers walking from one side of a square to the other and back, recording the birds encountered. Raptors and species considered to be accidental or migrating were not taken into account. We first looked for avifaunal, vegetation, and geomorphological gradients using Correspondence Analysis. As we found spatial autocorrelation within our response variables (avifaunal richness, abundance and/or composition), we first calculated an autocorrelation term, then added this autocorrelation term in anova , ancova (separate slope design) and stepwise regression to assess the relative role of spatial autocorrelation and environmental explanatory variables (vegetation, altitude, climate, or topography). We also partitioned the variance of the avifaunal matrix between several sets of co‐variables, after controlling for spatial effects, using a series of partial Canonical Correspondence Analyses. Results A main gradient, common to the two areas, distinguishes bird species characteristic of flat sedimentary areas and species dwelling in mountainous and/or rocky areas. Despite the generally low values of the correlations measured, we found that richness, abundance and composition of the avifauna were better correlated with topography, especially the altitudinal amplitude within each square, than any other variable, including vegetation. Altitudinal amplitude is related to substrate complexity. Main conclusions In arid zones of central Iran, topographic features seem to be the main factors structuring avifaunal composition and abundance. Avifaunal composition and richness are mainly correlated with the complexity of the substrate, but both avifaunal richness and abundance increase with altitude, probably in response to decreasing aridity. We did not observe any bird altitudinal zonation in a strict sense. These results contrast with those generally observed in mid‐latitude regions of the Palaearctic.     

藏中矿区珠芽蓼和尼泊尔酸模中重金属含量分析

西藏中部主要是指雅鲁藏布江河谷地带,包括拉萨、日喀则和泽当等地市,是西藏自治区的主要农区和工业矿区。西藏中部矿产资源丰富,其中cu的远景储量居全国第2位[1]。矿产的开发给当地居民带来巨大的经济效益,但同时也排放大量含有重金属的废渣、废水和废气,导致土壤重金属污染严重。土壤是中草药中重金属的主要来源之一,中草药中的重金属含量与地质背景有密切的关系,土壤中重金属元素的多寡在药用植物中都有所表现[2];土壤重金属污染对中草药品质有影响甚至危及人类健康[3]。近年来植物药在国际市场逐渐升温,传统医药在日益受到人们青睐的同时其质量与安全性也成为公众关注的焦点[4-6]。     

The dimeric assembly of Photobacterium leiognathi and Salmonella typhimurium SodC1 Cu,Zn superoxide dismutases is affected differently by active site demetallation and pH: an analytical ultracentrifuge study

To establish whether the species-specific variations at the subunit interface of bacterial Cu,Zn superoxide dismutases affect dimer assembly, the association state of the Photobacterium leiognathi (PlSOD) and Salmonella typhimurium (StSOD) enzymes, which differ in 11 out of 19 interface residues, was investigated by analytical ultracentrifugation.The same linkage pattern correlates quaternary assembly, active site metallation, and pH in the two enzymes albeit with quantitative differences. Both holo-enzymes are stable dimers at pH 6.8 and 8.0, although their shape is altered at alkaline pH. In contrast, dimer stability is affected differently by metal removal. Thus, apo-StSOD is a stable dimer at pH 6.8 whereas apo-PlSOD is in reversible monomer-dimer equilibrium. In both apoproteins a pH increase to 8.0 favors monomerization. These effects prove the existence of long-range communication between the active site and the subunit interface and provide a structural explanation for the known functional differences between the two enzymes.     

Genetic differentiation and species cohesion in two widespread Central American Begonia species

Begonia is one of the ten largest plant genera, with over 1500 species. This high species richness may in part be explained by weak species cohesion, which has allowed speciation by divergence in allopatry. In this study, we investigate species cohesion in the widespread Central American Begonia heracleifolia and Begonia nelumbiifolia, by genotyping populations at microsatellite loci. We then test for post-zygotic reproductive barriers using experimental crosses, and assess whether sterility barriers are related to intraspecific changes in genome size, indicating major genome restructuring between isolated populations. Strong population substructure was found for B. heracleifolia (F_ST=0.364, F′_ST=0.506) and B. nelumbiifolia (F_ST=0.277, F′_ST=0.439), and Bayesian admixture analysis supports the division of most populations into discrete genetic clusters. Moderate levels of inferred selfing (B. heracleifolia s=0.40, B. nelumbiifolia s=0.62) and dispersal limitation are likely to have contributed to significant genetic differentiation (B. heracleifolia Jost''s D=0.274; B. nelumbiifolia D=0.294). Interpopulation crosses involving a divergent B. heracleifolia population with a genome size ∼10% larger than the species mean had a ∼20% reduction in pollen viability compared with other outcrosses, supporting reproductive isolation being polymorphic within the species. The population genetic data suggest that Begonia populations are only weakly connected by gene flow, allowing reproductive barriers to accumulate between the most isolated populations. This supports allopatric divergence in situ being the precursor of speciation in Begonia, and may also be a common speciation mechanism in other tropical herbaceous plant groups.