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1.
Calcareous grasslands, most of which are man made and therefore depend on some kind of human interference for their maintenance, are among the most species-rich communities on Earth at a small scale. For many centuries, most of these grasslands have been used as extensive pasture. However, after 1900, and particularly from 1940 onwards, livestock grazing has declined throughout Europe leading to the abandonment of low intensity grasslands over large areas. To conserve the remaining grasslands or to restore recently abandoned grasslands, better insights about the effects of grassland management on above and belowground species diversity are needed. Here, we describe the results of an 11-year experiment to investigate the role of grassland management (grazing, mowing and abandonment) in determining species composition and diversity both in the aboveground vegetation and the seed bank of a calcareous grassland in Belgium. Species diversity declined by about 60% 11 years after abandonment, from 29 species m−2 to as few as 12 species m−2. Plots that were grazed remained constant in species richness, whereas mown sites lost about 20% of their original species. Abandoned plots were largely dominated by a few grass species, in particular Festuca rubra. Concomitant with changes in the aboveground vegetation, both the number of species found in the seed bank and seed density (number of seeds m−2) had changed significantly 11 years after abandonment. Species diversity and seed density were significantly lower in abandoned plots than in grazed or mown plots. We conclude that abandonment of calcareous grasslands may lead to rapid decline of plant species diversity both in the aboveground vegetation and in the seed bank. As a result, seed banks probably have a limited role to play in the restoration of recently abandoned grasslands.  相似文献   

2.
The leaf litter of six tropical tree species (Acacia holosericea, Acacia tortilis, Azadirachta indica, Casuarina equisetifolia, Cordyla pinnata and Faidherbia albida) frequently used in agroforestry plantations in Sahelian and Soudano-Sahelian areas were tested for their influence on soil nitrogen content, microbial biomass and plant growth under controlled greenhouse conditions. Half of the soil was planted with onion (Allium cepa L.) seedlings and the other half was not. Two herbaceous species, Andropogon gayanus and Eragrostis tremula, were also studied. Co-inertia analysis (CIA) and one-way analysis of variance (ANOVA) analysis showed that C. pinnata and F. albida leaf powder amendment induced the highest plant growth, whereas leaf powder of E. tremula is associated to higher microbial biomass and NH4+ content. Higher onion seedlings growth is associated with higher concentration of nitrogen and lignin in leaf powders. Conversely, lower plant growth is associated to higher rates of cellulose, hemicellulose and phenols in leaves. Higher rates of cellulose and hemicellulose are associated with higher microbial biomass and NH4+, whereas phenols are associated to lower microbial biomass. The results showed that amendment of A. holosericea leaf powder (high concentrations of phenol) to the soil resulted in a lower microbial biomass and lower onion seedlings growth. Data showed that the plant residue quality index (PRQI) could be a useful tool to predict the effects of litter materials on root growth in glasshouse conditions. The highest values on soil and plant parameters were recorded with C. pinnata litter. While powdered leaf material increased the accessibility of substrates to microbes, more research with C. pinnata leaf litter (under a wider range of ecological conditions) is needed. It could add deeper on its agronomic impact in the tropics.  相似文献   

3.
Saltmarshes, functionally important habitats in the marine–terrestrial ecotone that are regularly affected by tidal inundation, are mainly detritus-based in terms of fluxes of nutrients and energy. With respect to the mediating influence of saltmarsh detritivores on microbial colonisation of detritus and on decomposition processes, we tested whether the “intermediate disturbance hypothesis” (IDH) is also applicable to the effects of stress in this stressful environment. Decomposition experiments with litter of the cordgrass, Spartina anglica, and with terrestrial [Porcellio scaber (Isopoda)] and marine/semi-terrestrial [Orchestia gammarellus (Amphipoda)] detritivores as well as animal-free controls were carried out in an artificial saltmarsh system. Different daily flooding regimes served as experimental levels of stress. Both litter mass loss and microbial respiration were mostly higher under aquatic than under terrestrial conditions, no matter whether detritivores were present or not. Considering the intertidal zone, low to intermediate daily inundation rates resulted in increased microbial respiration and an increased influence of detritivores on litter mass loss in early stages of cordgrass decomposition with high rates of detritus mass loss, and intermediate tidal stress led to higher microbial cell counts throughout the entire experiment. Summarised over 3 months, regression analyses suggested that microbial activity and detritus mass loss show a trend towards highest values at low inundation rates and under permanent inundation, although microbial density was higher under longer daily inundation. Access to detritus by detritivores enhanced both litter mass loss and microbial respiration, especially in later decomposition stages, whereas microbial density was reduced by detritivores. In conclusion, we predict that overall the decomposition of cordgrass detritus in saltmarshes is promoted in the intermediate to high area of the intertidal zone with daily inundation of ca. 4–10 hours where both marine and terrestrial detritivores have access to promote decomposition processes through feeding and mediating microbial activity.  相似文献   

4.
Soil macroinvertebrates were studied in a Mediterranean-type forest on brown-pebble forest soils in southern Russia. At the site, 144 intact soil cores (76 cm2 each) forming a grid of 24 × 6 units were taken in order to determine animal spatial distribution. Abundance of isopods was 166.3 ± 16.0 indiv. m–2 and they constituted about 12% of the total macrofaunal abundance. Biomass of isopods was 3.5 g m–2, or about 21% of the total biomass of macrofauna. Three woodlice genera (Armadillidium, Cylisticus, and Trachelipus) were found at the site. The two latter genera formed almost all (93%) of the isopod population. We found that spatial distribution of woodlice was heterogeneous: areas with 4–5 individuals per sample were neighboring those without animals. In order to study soil factors influencing isopod distribution in the brown-pebble forest soil, the size of a sample was artificially increased by combining adjacent sample units. Litter mass (r = 0.41) and loss on ignition (LOI) (r = –0.55) significantly influenced isopod distribution. Soil pH was near neutral (6.79), LOI was 8.39, and the water holding capacity was 70.9%. Pebbles comprised up to 84% of the sample's mass. Ca. 40 samples are recommended for estimation of isopod abundance in brown forest soil.  相似文献   

5.
The diversity of Oniscidea across a 1000-m altitudinal gradient comprising three distinct environments—the coastal plain, the highland slopes, and the highlands—was described and analysed. We employed 1 h-long exploratory manual sampling at 41 sites. Fourteen species were identified, of 818 individuals collected. Sampling-effort curves stabilised for all three environments; analytical estimates of species richness did not exceed the observed value. Abundance did not vary significantly among environments, and local species richness differed only marginally. However, the Shannon diversity index for local sites indicated highland slopes to be significantly more diverse than the coastal region; the same was true for bootstrap estimates at the regional level. Two species appeared in all three environments, comprising 72.7% of the abundance. The coastal region and highlands had one exclusive species each, and the highland slopes had three. The first two environments are more similar to each other than to the slopes, although they are not contiguous. The altitudinal gradient of diversity was hump-shaped, because the highland slopes were most diverse. The reasons for this pattern are not biogeographical; that is, the highland slopes are not a contact zone between the highlands and the coast. A complete explanation depends upon better understanding of the effect of soil type and terrain slope on the diversity of terrestrial isopods.  相似文献   

6.
Strains belonging to Paenibacillus durus isolated from the rhizosphere of various grasses and from bulk soil were previously divided into five phenotypic groups (A1–A5) based on the fermentation pattern of six carbohydrates (A1: sorbitol (+), A2: dulcitol and tagatose (+), A3: starch and glycogen (+), A4: starch, glycogen and d-arabitol (+) and A5: negative for these carbohydrates). This study aimed to assess whether plant types select for specific P. durus phenotypic groups. For that purpose, polymerase chain reaction-restriction fragment length polymorphism analysis of part of genes encoding 16S rRNA (ARDRA) and DNA gyrase subunit B (gyrB-RFLP) were used to produce genetic fingerprints. ARDRA and gyrB-RFLP data were clustered together to generate a dendrogram and two main clusters were observed. Cluster I showed a predominance of strains isolated from wheat, maize and sugarcane rhizospheres. Strains isolated from maize were distributed among the five patterns of carbohydrate metabolism, while strains isolated from sugarcane showed to be predominantly able to metabolize starch and glycogen. Neither sorbitol- nor arabitol-metabolizing strains were found in cluster II, which consisted of strains isolated from soil and from all plant species used. Our results suggest that the plants influenced the diversity of P. durus in their rhizospheres.  相似文献   

7.
An Allee effect occurs when at low densities there is a positive relationship between density and fitness leading to a higher probability of extinction. One circumstance in which it may arise is when isolated individuals are less effective in modifying their environment in a favourable way than groups of individuals. In this paper we use Porcellio scaber to test the hypothesis that the fitness correlate of growth rate will vary as a function of density not just due to the negative effects of increasing interference competition whilst foraging at higher densities, but also positively at lower densities due to isolated individuals spending more time and energy searching for other individuals with which to aggregate whilst sheltering.Below densities of 70 m–2 relative growth rates increased as a function of density, above 70 m–2 growth rate decreased with increasing density. Time spent walking and searching increased at lower densities. These behavioural observations, together with the original observations on water loss and oxygen consumption made by Allee [1], are used to interpret the curvilinear growth rate response to density as an example of a component Allee effect, which is discussed in relation to the importance of aggregation as an adaptation to the terrestrial environment in the Oniscidea.  相似文献   

8.
[目的]探究围封对内蒙古希拉穆仁草地物种多样性的影响,为围封对草原物种多样性影响的过程研究提供科学依据。[方法]通过调查、计算内蒙古希拉穆仁放牧草地与连续11 a围封草地的物种多样性,结合当地年降水量数据,分析放牧草地围封后物种多样性特征。[结果]围封后,冷蒿、轮叶委陵菜、达乌里芯芭、二裂委陵菜、星毛委陵菜年际波动较大;围封降低了希拉穆仁草地物种多样性,降水量较少年份(年降水量200 mm的2014年)Simpson,Shannon-Wiener和Pielous指数则刚好相反;围封后物种丰富度与年降水量相关系数减小。[结论]长期围封导致希拉穆仁草地物种多样性下降。在干旱气候环境下,围封能够一定程度地缓解气候变化对希拉穆仁草地物种多样性的影响。  相似文献   

9.
This study aimed at identifying the factors that affected the survival of faecal coliforms as measured by E. coli in four types of soils in Botswana which were amended with sewage sludge. Physico-chemical and biochemical properties and coliform population in the different soils, sludge, and soil/sludge mixtures were determined after sampling, on composing the soil/sludge mixtures, and 90 days after composing. Coliform population in the different soil/sludge mixtures decreased by about 90% after 90 days. The age of the sludge used and the rate at which it was applied to the soils initially determined the population of E. coli in each soil/sludge mixture, but after 90 days, differences inherent in the different soil types were the main determinants of the E. coli population. Percentage reduction of coliforms in Type 1 sludge mixtures were lower (38%) than in Type 2 sludge mixtures (57%). Up to 79.8% of the reduction observed in E. coli population in the Barolong luvisol-sludge mixtures after 90 days was caused by reduction in pH and moisture content, while 72.6%, 84.5% and 55.1% of the reduction in E. coli population in Tuli luvisol-, arenosol- and vertisol-sludge mixtures, respectively, was accounted for by the reduction in moisture content and Olsen P concentration. Coliform survival rates varied with soil types being 12%, 6.4%, 5.3% and 5.8% for the vertisol, arenosol, Barolong luvisol and Tuli luvisol, respectively. A minimum period of 90 days should be allowed between when sludge is applied to similar soils and when seeds are sown. The exact period should, however, be determined by the properties of the soil with fine-textured soils requiring a longer period than coarse-textured soils.  相似文献   

10.
The purpose of this study was to assess the spatial variability of the activity of three hydrolytic enzymes, i.e. urease activity (UAc), alkaline phosphatase activity (APAc), and arylsulfatase activity (ASAc), in pasture topsoils using geostatistics. Enzyme activities along a transect in a 1.35-ha pasture were determined using 77 soil samples from the upper 20 cm of soil. UAc varied from 101.0 to 182.7 μg N g−1 soil h−1; APAc varied from 1.56 to 3.62 μg p-nitrophenol g−1 soil h−1; and ASAc varied from 1.50 to 3.26 μg p-nitrophenol g−1 soil h−1. The linear models fit the best semivariogram models for UAc, APAc, and ASAc. Semivariograms for enzyme activities exhibited spatial dependence with ranges of influence of approximately 124.7 m.  相似文献   

11.
Communities of arbuscular mycorrhizal fungi (AMF) are strongly affected by land use intensity and soil type. The impact of tillage practices on AMF communities is still poorly understood, especially in organic farming systems. Our objective was to investigate the impact of soil cultivation on AMF communities in organically managed clay soils of a long-term field experiment located in the Sissle valley (Frick, Switzerland) where two different tillage (reduced and conventional mouldboard plough tillage) and two different types of fertilization (farmyard manure & slurry, or slurry only) have been applied since 2002. In addition, a permanent grassland and two conventionally managed croplands situated in the neighborhood of the experiment were analyzed as controls. Four different soil depths were studied including top-soils (0–10 and 10–20 cm) of different cultivation regimes and undisturbed sub-soils (20–30 and 30–40 cm). The fungi were directly isolated from field soil samples, and additionally spores were periodically collected from long-term trap culture (microcosm) systems. In total, >50,000 AMF spores were identified on the species level, and 53 AMF species were found, with 38 species in the permanent grassland, 33 each in the two reduced till organic farming systems, 28–33 in the regularly plowed organic farming systems, and 28–33 in the non-organic conventional farming systems. AMF spore density and species richness increased in the top-soils under reduced tillage as compared to the ploughed plots. In 10–20 cm also the Shannon–Weaver AMF diversity index was higher under reduced tillage than in the ploughed plots. Our study demonstrates that AMF communities in clay soils were affected by land use type, farming system, tillage as well as fertilization strategy and varying with soil depth. Several AMF indicator species especially for different land use types and tillage strategies were identified from the large data set.  相似文献   

12.
Management intensity modifies soil properties, e.g., organic carbon (Corg) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (Pmic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling Pmic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on Pmic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (Cmic), Pmic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, Pmic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil Corg is the profound driver of plant diversity effects on Pmic in grasslands. For both forest and grassland, we found regional differences in Pmic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on Pmic due to a lack of effects on controlling variables (e.g., Corg). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling Pmic or Cmic in soil differ in part and that regional differences in controlling variables are more important for Pmic in soil than those induced by management.  相似文献   

13.
[目的]分析3种不同草地退化阶段(轻度退化,中度退化和重度退化)草地植被和土壤理化特性的变化规律,为类似区域退化草地植被恢复提供有效途径。[方法]野外植被调查、土壤取样和室内分析。[结果]草地退化不同阶段草地植物群落组成和物种多样性均有差异,退化对草地土壤理化特性有明显影响。重度退化草地土壤容重显著高于轻度退化草地(p0.05)。轻度和中度退化样地0—10cm土壤空隙度显著高于重度退化草地。重度退化草地的土壤有机质、全碳、全钾、全磷和有效钾均明显小于轻度退化草地(p0.05),但土壤pH值和有效氮含量没有显著变化。[结论]高山草地退化演替对该区土壤物理特性具有显著影响。  相似文献   

14.
The conservation of biodiversity critically depends on the value that humans attach to it. Apart from an ecological and economic value, an aesthetic value has often been assigned to biodiversity. However, it is not known whether lay people appreciate the diversity of species and not just certain individual species or nature as a whole. We studied in a series of experiments and field studies people’s perception and appreciation of species diversity. We presented meadow-like arrays of different species richness and evenness but random species composition to lay people and asked them to estimate plant species richness and rank the arrays by attractiveness. The experiments were complemented by two larger-scale field studies using natural meadows. Both in the experiments and the field studies the mean perception of species richness by people increased with true species richness, but was slightly overestimated at low and increasingly underestimated at high diversity levels. Lay people’s aesthetic appreciation of both the experimental grassland arrays and the natural meadows increased with true species richness. Communities consisting of the same number of species were perceived to be more species-rich and were appreciated more when their evenness was high. Our results demonstrate that plant diversity in itself is attractive to humans. The current reduction of the diversity of grasslands due to intensification of management may thus reduce the attractiveness of regions where grasslands are a dominant feature of the landscape. This could have negative consequences for tourism and may add an economic argument for the conservation of biodiversity in grasslands.  相似文献   

15.
The myrmecophilous Platyarthrus schoblii Budde-Lund, 1885 is widely distributed and native in the Mediterranean region. In Hungary it was first found at Budapest, in 2001, in a colony of Lasius neglectus van Loon, Boomsma and Andrásfalvy, 1990 (Hymenoptera: Formicidae). This invasive and polygynous ant species is dispersing in an antropochorous way throughout Europe. There are 16 known colonies of L. neglectus in Hungary. Fourteen of them have been surveyed for the isopod, which was detected in eight cases (57%). In addition to L. neglectus, the isopod has been recently found with other native ant species [Lasius niger (Linnaeus, 1758), Lasius emarginatus (Olivier, 1791) and Tetramorium caespitum (Linnaeus, 1758)] in the country. We have also found the joint occurrence of P. hoffmannseggii Brandt, 1833 and P. schoblii. The co-occurrence and joint expansion of the ranges of L. neglectus and P. schoblii indicates their co-habitation and antropochorous dispersal while the appearance with L. emarginatus, L. niger and T. caespitum supports our hypothesis about possible adoption by different ant species.  相似文献   

16.
Past semi-natural grassland extent is thought to have a major influence on contemporary species richness in rural landscapes. The loss of grasslands over the last 300 years was reconstructed for 12 rural landscapes in Sweden, ranging from open modern agricultural landscapes to more forested landscapes. Old maps and aerial photographs from 1950s and today were used to reconstruct landscape patterns in four time-steps to investigate how present plant species richness relates to past grassland extent and decline in old and new grassland habitats. The relative importance of soil properties on the timing of grassland decline was assessed. Plant species occurrence was recorded in managed and abandoned grassland habitats in each landscape.Past and present grassland distribution was a major factor in determining plant species patterns found in grasslands today. All landscapes had an average of 80% grassland 300 years ago. Since then grassland has declined by 90% across all landscapes. Proportion of clay soils influenced the timing of grassland decline, where grasslands in landscapes dominated by clay soils were conversed to crop-fields more than 100 years ago. Grasslands on coarser soils declined later, primarily to forest. Landscapes with more than 10% semi-natural grassland left today had 50% higher species richness in all grasslands, including both abandoned and new grassland. Time since major grassland decline also seems to have an effect on the landscapes’ species richness. The results show that plant species patterns in grasslands at local scales are determined by broader landscape processes which may have occurred many centuries ago.  相似文献   

17.
The effects of grazing intensity on plant and insect diversity were examined in four different types of grassland (intensively and extensively cattle-grazed pastures, short-term and long-term ungrazed grassland; 24 study sites). Vegetation complexity (plant species richness, vegetation height, vegetation heterogeneity) was significantly higher on ungrazed grasslands compared to pastures but did not differ between intensively and extensively grazed pastures. However, insect species richness was higher on extensively than on intensively grazed pastures, established by suction sampling of four insect taxa (Auchenorrhyncha, Heteroptera, Coleoptera, Hymenoptera Parasitica). This may be due to intensive grazing disrupting plant-insect associations as predicted by a “trophic-level” hypothesis. Local persistence and small-scale recolonization of insects on plants appeared to be difficult in the highly disturbed environment of intensive grazing. Insect diversity increased across the four treatments in the following order: intensively grazed<extensively grazed<short-term ungrazed<long-term ungrazed. The major predictor variable of differences in species diversity was found to be vegetation height. Predator-prey ratios within the investigated insect groups were not affected by grazing intensity.  相似文献   

18.
东祁连山不同退化草地植物群落特征与土壤养分特性   总被引：1，自引：0，他引：1  
为探究东祁连山不同退化草地植物群落特征、土壤养分特性及其相关性,以轻度退化草地、中度退化草地和重度退化草地为研究对象,采用野外调查、室内测定和数据统计分析相结合的方法,分析了不同退化草地植被特征、土壤养分特性及其之间的相关性。结果表明:(1)从轻度退化草地-重度退化草地,植物群落特征(地上生物量、高度、密度、频度和总盖度)整体呈现降低趋势,且差异显著(P<0.05),中度退化草地Margalef指数、Shannon指数和Evenness指数最高,Dominance指数最低;(2)研究区植物共有19科38属41种,生态适应性较强的植物主要集中在豆科、禾本科、菊科和蔷薇科,不同退化草地植被型分别为矮生嵩草(K.humilis)+赖草(Leymus secalinus)、矮生嵩草+高山唐松草(Thalictrum alpinum)、矮生嵩草+赖草,其中矮生嵩草是各退化草地的优势种,不同退化草地的功能群以杂类草占优势,其次是禾草类,毒草类所占的比例最少;(3)随草地退化程度加重,土壤速效氮、有效磷、有机碳和含水量呈降低的趋势,而pH整体呈现升高的趋势;(4)不同退化草地土壤因子对植被生长贡献率最高分别为速效氮、有效磷和含水量。综上,随着草地退化程度加重,植物群落结构向单一趋势过渡,土壤养分含量减少,且土壤因子对植物贡献率也相应发生变化。  相似文献   

19.
A field study was conducted in the province of Burgos (Castile, NW of Spain) to assess the role and influence of the different anthropic use of soil on the oribatid mite communities (Acari, Oribatida).Soil samples from 20 representative soil sites of the Castilian upland steppes, with cultured, pastureland or forest soil uses, were taken in spring and autumn 2000. Thereafter, soil samples were analysed in terms of their mesofaunal biodiversity, measured using the real and relative diversity of the oribatid mite communities.Collected individuals were identified to species level, being altogether 111 Oribatid species. Results from communities' ordination analysis showed clear gradients based on community variables. One of these was defined by plots with high values of diversity and species richness which correspond to the less anthropic natural soils, mainly oak forest. In contrast, the most anthropic agrosystems soils, including extensive cereal crops, most of them receiving only mineral fertilisation or having human management, were placed in opposite gradients. Differences in biodiversity between crop lands and natural soils were also confirmed by ANOVA. The seasonality, measured in terms of difference between spring and autumn plots, played a minimum role in explaining differences of diversity. Nevertheless autumn diversity values were slightly higher than those of spring, except for crops.  相似文献   

20.
The restoration of drained peat bogs in Northwest (NW) Europe is an important task of soil protection, but needs to cope with warmer and drier summers. Our examination took place in the Pietzmoor bog (Schneverdingen, NW Germany) that had been drained for fuel peat extraction until the 1970s and rewetted since then. We determined carbon dioxide (CO2) efflux in situ and in laboratory incubations. Also, we analyzed pore water for dissolved organic carbon (DOC), total and dissolved organic N (DON), nitrate (NO3–) and ammonium (NH4+) concentration. In Schneverdingen, the summer 2003 was record-breaking hot (mean temperature June to August elevated > 3 K compared to long-term average) and dry (precipitation during the same period < 59% of long-term average). In July 2003, the water table in the Pietzmoor subsided to > 42 cm below the surface in July 2003, when in situ soil CO2 efflux was up to 23.4 g m–2 d–1 compared to 15.7 g m–2 d–1 in September. Prior to March 2003, DOC concentrations in pore water were < 180 mg l–1 and NH4+ was the dominant fraction of mineral N. In July 2003, DOC concentration rose to 249 g l–1, DON concentrations more than doubled, and NO3– became the dominant fraction of mineral N. Due to the increased future likelihood of hot and dry summers in NW Germany, peat bog restoration efforts need take care that a water table close to the surface is maintained.  相似文献   

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