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.     

Soil microarthropods and macrofauna in monsoon tropical forests of Cat Tien and Bi Dup-Nui Ba National Parks,southern Vietnam

The abundance, biomass, vertical distribution, and taxonomic composition of soil invertebrates (springtails, macrofauna, and termites) were studied in forest formations differing in edaphic and climatic conditions: lowland forests dominated by Lagerstroemia spp. or Dipterocarpus spp. in the Cat Tien National Park and in a mountain pine (Pinus kesiya) forest on the Da Lat Plateau, southern Vietnam. In the lowland forests, springtails had a relatively low density (10000–12000 ind./m²), but their diversity was high (41–43 species in each forest). The density of large soil invertebrates (without ants and termites) reached 500–700 ind./m² at a biomass of approximately 30 g/m² (with earthworms accounting for up to 230 ind./m² and 19–28 g/m²). Among termites, species of the genera Macrotermes and Odontotermes were dominant. Their total biomass in some areas exceeded 15–20 g/m². In the mountain pine forest, the total biomass of soil macrofauna was approximately 11 g/m², the abundance and diversity of springtails were low (7500 ind./m², 28 species), and wood-destroying species of the genera Schedorhinotermes sp. and Coptotermes sp. dominated among termites.     

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

Despite the major importance of soil biota in nutrient and energy fluxes, interactions in soil food webs are poorly understood. Here we provide an overview of recent advances in uncovering the trophic structure of soil food webs using natural variations in stable isotope ratios. We discuss approaches of application, normalization and interpretation of stable isotope ratios along with methodological pitfalls. Analysis of published data from temperate forest ecosystems is used to outline emerging concepts and perspectives in soil food web research. In contrast to aboveground and aquatic food webs, trophic fractionation at the basal level of detrital food webs is large for carbon and small for nitrogen stable isotopes. Virtually all soil animals are enriched in ¹³C as compared to plant litter. This ‘detrital shift’ likely reflects preferential uptake of ¹³C‐enriched microbial biomass and underlines the importance of microorganisms, in contrast to dead plant material, as a major food resource for the soil animal community. Soil organic matter is enriched in ¹⁵N and ¹³C relative to leaf litter. Decomposers inhabiting mineral soil layers therefore might be enriched in ¹⁵N resulting in overlap in isotope ratios between soil‐dwelling detritivores and litter‐dwelling predators. By contrast, ¹³C content varies little between detritivores in upper litter and in mineral soil, suggesting that they rely on similar basal resources, i.e. little decomposed organic matter. Comparing vertical isotope gradients in animals and in basal resources can be a valuable tool to assess trophic interactions and dynamics of organic matter in soil. As indicated by stable isotope composition, direct feeding on living plant material as well as on mycorrhizal fungi is likely rare among soil invertebrates. Plant carbon is taken up predominantly by saprotrophic microorganisms and channelled to higher trophic levels of the soil food web. However, feeding on photoautotrophic microorganisms and non‐vascular plants may play an important role in fuelling soil food webs. The trophic niche of most high‐rank animal taxa spans at least two trophic levels, implying the use of a wide range of resources. Therefore, to identify trophic species and links in food webs, low‐rank taxonomic identification is required. Despite overlap in feeding strategies, stable isotope composition of the high‐rank taxonomic groups reflects differences in trophic level and in the use of basal resources. Different taxonomic groups of predators and decomposers are likely linked to different pools of organic matter in soil, suggesting different functional roles and indicating that trophic niches in soil animal communities are phylogenetically structured. During last two decades studies using stable isotope analysis have elucidated the trophic structure of soil communities, clarified basal food resources of the soil food web and revealed links between above‐ and belowground ecosystem compartments. Extending the use of stable isotope analysis to a wider range of soil‐dwelling organisms, including microfauna, and a larger array of ecosystems provides the perspective of a comprehensive understanding of the structure and functioning of soil food webs.     

Sea and colonial-nesting birds of islands in the southern part of Amurskii Liman

The quantity of the nesting couples of sea birds on the islands of the southern part of Amurskii Liman was determined: common heron Ardea cinerea, slaty-backed gull Larus schistisagus, black-tailed gull L. crassirostris, and sooty guillemot Cepphus carbo.     

Termites (Isoptera) in forest ecosystems of Cat Tien National Park (Southern Vietnam)

The species composition, abundance and colony sizes of terrestrial termites were studied in five forest habitats of Cat Tien National Park, Southern Vietnam. Twenty-four species belonging to Rhinotermitidae (1 species) and Termitidae (23 species, mostly Macrotermitinae), were found in mounds and in soil samples. The density of inhabited termite nests in different habitats averaged 68 per hectare (range 44–106), most nests belonged to Macrotermes spp. Six mounds of dominant species (Globitermes sulphureus, Microcerotermes burmanicus, Macrotermes carbonarius, M. gilvus, M. malacensis and Hypotermes obscuriceps) were destructively sampled. The number of termites in the nests ranged from 65 000 to 3 150 000 individuals with the biomass ranging from 185 to 2440 g live weight. The abundance of foraging termites in soil and litter averaged 60 ind./m2.The total abundance of Macrotermes species alone could conservatively be estimated as 2.5 million individuals and 20.5 kg live weight per hectare. Four species dominating in the studied habitats (M. carbonarius, M. gilvus, M. malaccensis, and H. obscuriceps) belong to active litter decomposers.     

Trophic positions and niche segregation of two anuran species in the ecosystem of a forest lake

Hydrobiologia - Different species of amphibians often breed in the same water bodies and their diets overlap. Theoretically, this might lead to a competitive elimination of either one but there are...     

Intraspecific Variability of the Shape of the Lower Third Premolar in Ochotona hyperborea (Pallas 1811)

Biology Bulletin - The shape variability of the chewing surface of the third lower premolar (p3) was analyzed in modern members of the Northern Pika (Ochotona hyperborea). The variability in the...