On some properties of the Bray-Curtis dissimilarity and their ecological meaning

In this paper, we examine some basic properties of the Bray-Curtis dissimilarity as compared with other distance and dissimilarity functions applied to ecological abundance data. We argue that the ability of every coefficient to measure species-level contributions is a fundamental requirement. By suggesting an additive decomposition formula for the Bray-Curtis coefficient we derive a general formula of dissimilarity, which includes the Canberra distance and the Bray-Curtis dissimilarity as special cases. A similar general formula is also proposed for the Marczewski-Steinhaus coefficient. Finally, using a modified version of Dalton’s principle of transfers, we show that the Bray-Curtis coefficient and the city-block distance exhibit a linear response to the transfer of species abundances from an abundant plot to a less abundant plot. At the other extreme, the chord and the Hellinger distances show an irregular and non-monotonic behavior.     

The preparation of microtome sections of unaltered soil for the study of soil organisms in situ

Summary A new technique for study of small soil organisms in situ in unaltered soil is described.The soil samples are cooled in a refrigerator at — 10°C to kill the animals. A small portion taken from a frozen soil sample, is slowly immersed in a solution of gelatin. When the specimen is infiltrated with gelatin and the whole cooled it is fixed in formalin to enable it to withstand treatment with hydro-fluoric acid for removal of sand grains. Subsequently the specimens are immersed in gelatin solution for a second time after which the specimens are affixed to wooden blocks which can be clamped in the microtome. Before sectioning, the embedded specimen affixed to the wooden block is hardened in methylalcohol after which it is possible to cut sections 7,5–10µ thick.The most satisfactory staining procedure proved to be the quadruple staining method of Johansen. By this method nematodes, fungi, bacteria and amoebae are easily distinguishable from the soil particles.     

Microsatellites and their application to population genetic studies

Microsatellites may soon become the markers of choice for molecular population genetic studies. However, our knowledge of these simple repetitive sequences and how they evolve in natural populations is far from complete. We highlight some recent results of population studies and advances in our ability to interpret some of the allele frequency distributions that we are beginning to observe.     

The survival of some soil mites at different humidities and their reaction to humidity gradients

The survival at different humidities of 10 species of soil mites in larval, nymphal and adult stages has been investigated. The immature forms are almost as resistant as mature but differences exist between species. Moisture preferences were also investigated and some form of ortho-kinesis may explain the results.

---

Zusammenfassung Acht Oribatiden- und zwei Uropodiden-Arten wurden einem Feuchtigkeitsgefälle von völliger Sättigung bis zu 13% rel. Luftfeuchtigkeit ausgesetzt. Erwachsene Pelops acromios, Cepheus dentatus und Odontocephus elongatus zeigten sowohl bei 10° wie bei 20° in allen Feuchtigkeitsstufen nach drei Tagen eine 100% ige Überlebensrate. Ceratoppia bipilis, Oribata gracilipes und Euzetes seminulum wiesen bei niederer Luftfeuchtigkeit erhöhte Sterblichkeit auf und bei 13% rel. Luftfeuchtigkeit betrugen ihre Überlebensraten nach drei Tagen 75, 55 bzw. 45%. Hermannia gibba, Platynothrus peltifer, Olodiscus integra und Cilliba cassidea zeigten unter 55% rel. Luftfeuchtigkeit alle einen plötzlichen Abfall der Überlebensrate und am Ende von drei Tagen blieben nur wenige Individuen am Leben. Die Fähigkeit der larvalen und Nymphenstadien, erniedrigte Luftfeuchtigkeit zu ertragen, war im allgemeinen etwas geringer als bei den Adulten, doch zeigten die Arten untereinander die gleiche relative Resistenz wie bei den Erwachsenen. In einer alternativen Wahlkammer, die ein Feuchtigkeitsgefälle aufwies, bevorzugten alle Arten die feuchtere Hälfte. Nur wenn die Wahl zwischen 94% und 100% rel. Luftfeuchtigkeit geboten wurde, bevorzugten P. acromios, C. dentatus und O. elongatus die geringere Feuchte. Die Ergebnisse weisen darauf hin, daß eine Form von Orthokinese vorliegt und noch kein Unterschied in der Anzahl der Individuen beobachtet wurde, die sich bei gleichmäßiger Feuchtigkeit von 10, 47 und 100% rel. Luftfeuchtigkeit bewegten. Im Vergleich zwischen feuchten und trockenen Bedingungen besteht kein wahr nehmbarer Sensibilitätsunterschied.

     

Stable isotopes of carbon and nitrogen in soil ecological studies

The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (¹²C/¹³C and ¹⁴N/¹⁵N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field.     

The further preparation of inorganic cationic yeasts and some of their chief properties

1. A method is described for replacing the intracellular K(+) of the yeast cell by Rb(+), Cs(+), Li(+) or Ca(2+) ions. In the formation of a calcium yeast it is necessary to proceed first through a sodium yeast (Conway & Moore, 1954) as in the formation of a magnesium yeast (Conway & Beary, 1962). This concludes the series of such yeasts in which almost all the usual K(+) is replaced by another cation, and for which the effect on the properties of fermentation, oxygen uptake and of growth are described. 2. Previous work has shown that all these inorganic cations that can be accumulated in quantity at pH7.0 are taken up by the same carrier, that the uptake of Mg(2+) is almost completely inhibited by anoxia and cyanide (0.2mm) and that in the uptake of Mg(2+) ions a practically equivalent amount of H(+) ions is excreted. It is suggested that these facts amount to a definitive demonstration that the carrier is a cytochrome.     

Enzymatic preparation of chitooligosaccharides and their anti-obesity application

ABSTRACT

Chitooligosaccharides (COS) are derived from chitosan, which can be used as nutraceuticals and functional foods. Because of their various biological activities, COS are widely used in the food, medicine, agriculture, and other fields. COS were prepared by chitosanase from Pseudoalteromonas sp. SY39 and their anti-obesity activity was researched in mice in this study. The effects of hydrolysis time, temperature, the ratio of enzyme to chitosan, and pH on the productivity of COS were discussed. Preparation process of COS was established in a 5-L fermenter. COS were characterized and their anti-obesity activity was studied in animal experiments. The results showed that COS could effectively reduce serum lipid levels and obesity in mice, and have a good anti-obesity activity. The preparation technology and remarkable anti-obesity activity of COS further expand their applications in the food and pharmaceutical industries.     

Technique for ecological studies of seed germination in relation to soil water potential

Summary Seeds were germinated in soils of known matric potential (ψ_m) achieved by adding the requisite amount of water to air-dry soil and mixing for several days. The quantity of water was derived from calibration curves of water content against ψ_m by use of pressureplate extraction equipment. Soils were transferred to plastic Petri dishes in which seeds were sown. Variations of the technique permitted germination counting through the transparent dish lid, or by opening the dish and either resealing or discarding the replicate dish. Measurements of ethylene and carbon dioxide in the soil atmosphere suggest that neither gas accumulated to a level which could interfere with interpretation of results. Some species showed sensitivity of germination to water potential which was correlated with the relative wetness of their habitats.     

Phytosociological amplitudes of some Dutch coastal species and their ecological interpretation

A 4-axis Reciprocal Averaging ordination of phytosociological tables of Dutch plant communities revealed environmentally interpretable gradients: (1) overall moisture, (2) salinity, (3) soil fertility, and (4) structural complexity of vegetation. The quantitative occurrence of all species along these gradients has been computed. Some examples of the distribution of species from coastal communities are given, to show how these data may help to summarize and visualize existing knowledge and how they can form a basis for further study.Nomenclature of species follows Heukels-van Ooststroom (1975), that of syntaxonomical units Westhoff & den Held (1969).     

转Bt基因作物对土壤节肢动物的生态风险性

土壤节肢动物在土壤生态系统物质循环中起着非常重要的作用,因此人们越来越关心转基因作物对土壤节肢动物的生态安全性。本文在介绍转基因作物对土壤节肢动物影响机制的基础上,重点论述了土壤跳虫、螨类、甲虫、水生昆虫等节肢动物对不同转基因作物响应的研究进展,旨在为科学全面的开展转基因作物土壤生态风险评价提供参考。     

Preferential use of root litter compared to leaf litter by beech seedlings and soil microorganisms

Background and aims

Litter decomposition is regulated by e.g. substrate quality and environmental factors, particularly water availability. The partitioning of nutrients released from litter between vegetation and soil microorganisms may, therefore, be affected by changing climate. This study aimed to elucidate the impact of litter type and drought on the fate of litter-derived N in beech seedlings and soil microbes.

Methods

We quantified ¹⁵N recovery rates in plant and soil N pools by adding ¹⁵N-labelled leaf and/or root litter under controlled conditions.

Results

Root litter was favoured over leaf litter for N acquisition by beech seedlings and soil microorganisms. Drought reduced ¹⁵N recovery from litter in seedlings thereby affecting root N nutrition. ¹⁵N accumulated in seedlings in different sinks depending on litter type.

Conclusions

Root turnover appears to influence (a) N availability in the soil for plants and soil microbes and (b) N acquisition and retention despite a presumably extremely dynamic turnover of microbial biomass. Compared to soil microorganisms, beech seedlings represent a very minor short-term N sink, despite a potentially high N residence time. Furthermore, soil microbes constitute a significant N pool that can be released in the long term and, thus, may become available for N nutrition of plants.     

Epstein-barr virus replication studies and their application to vector design

Vectors containing elements of the Epstein-Barr virus genome are used primarily to maintain cloned DNA inserts as plasmids in mammalian cells. However, Epstein-Bar-virus-based vectors have also been valuable tools in the hands of those studying the life cycle of Epstein-Barr virus. In this article, we discuss those characteristics of Epstein-Barr virus and its life cycle that have been used in vector construction and describe methods that are particularly applicable to the use of Epstein-Barr-virus-based vectors.     

The application of ecological theory to palaeoecological studies, with special reference to equilibrium theory and the Ordovician System

In the light of recent applications of equilibrium theory to palaeoecological investigation, the origins and scope of the model are reviewed as a perspective for considering the viability of such applications in the analysis of Ordovician faunal associations. Alternative methods for the detection of immigration and emigration patterns are advanced in favour of other recently proposed techniques. The mid-Caradoc Gelli-grin Formation is used as an example of a well sampled fossiliferous deposit from which comprehensive faunal data can be derived for use in the detection of intra-association fluctuations in faunal composition. Different methods of defining such fluctuations are shown to produce consistent results. 'Saturation', 'area effect' and 'overshoot effect' are all shown to be aspects of equilibrium theory with potential for application in the palaeoecological field. The calculation of the coefficient of variation for eight faunal associations discussed here is shown to be a useful method for the determination of the degree of saturation of such associations; comparable associations show similar saturation values.     

The influence of litter quality and micro-habitat on litter decomposition and soil properties in a silvopasture system

Studies to understand litter processes and soil properties are useful for maintaining pastureland productivity as animal husbandry is the dominant occupation in the hot arid region. We aimed to quantify how micro-habitats and combinations of litters of the introduced leguminous tree Colophospermum mopane with the grasses Cenchrus ciliaris or Lasiurus sindicus influence decomposition rate and soil nutrient changes in a hot desert silvopasture system. Litter bags with tree litter alone (T), tree + C. ciliaris in 1:1 ratio (TCC) and tree + L. sindicus 1:1 ratio (TLS) litter were placed inside and outside of the C. mopane canopy and at the surface, 3–7 cm and 8–12 cm soil depths. We examined litter loss, soil fauna abundance, organic carbon (SOC), total (TN), ammonium (NH₄–N) and nitrate (NO₃–N) nitrogen, phosphorus (PO₄–P), soil respiration (SR) and dehydrogenase activity (DHA) in soil adjacent to each litter bag. After 12 months exposure, the mean residual litter was 40.2% of the initial value and annual decomposition rate constant (k) was 0.98 (0.49–1.80). Highest (p < 0.01) litter loss was in the first four months, when faunal abundance, SR, DHA and humidity were highest but it decreased with time. These variables and k were highest under the tree canopies. The litter loss and k were highest (p < 0.01) in TLS under the tree canopy, but the reverse trend was found for litter outside the canopy. Faunal abundance, litter loss, k, nutrient release and biochemical activities were highest (p < 0.01) in the 3–7 cm soil layer. Positive correlations of litter loss and soil fauna abundance with soil nutrients, SR and DHA demonstrated the interactions of litter quality and micro-habitats together with soil fauna on increased soil fertility. These results suggest that a Colophospermum mopane and L. sindicus silvopasture system best promotes faunal abundance, litter decomposition and soil fertility. The properties of these species and the associated faunal resources may be utilised as an ecosystem-restoration strategy in designing a silvopasture system. This may help to control land degradation and increase productivity sustainably in this environment.     

Downhill movement of litter and its implication for ecological studies in three types of forest in Japan

The amount of litter moving down the slope was measured in three types of forest, together with an examination of rain as a factor in bringing this about. The three forest types were a natural mixed stand ofPinus densiflora and hardwood trees (plot A), aCryptomeria japonica plantation (plot S) and aChamaecyparis obtusa plantation (plot H). The amount of moved litter was quite large in plots A and H, but relatively small in plot S. The rain factor had little influence on litter movement in plot A, but was the main cause of movement in plot S and (especially) plot H. It is suggested that measurement of litter input and output not only by traps above ground level, but also by ones on the ground is essential for determining the cycling of elements inC. obtusa forests. It is also suggested that the decomposition of leaf litter should be studied both on the soil surface and in the soil inC. obtusa forests.