Damien Ertlen

Vegetation history of chernozems in the Czech Republic

Chernozem is a soil type which can be characterised by a thick dark surface horizon, which consists of organic matter and tends to change into a carbonate horizon or more often into a loess horizon. Chernozem is defined as a zonal soil that has developed under steppe vegetation in a dry continental climate. Nevertheless, chernozems can also be found in central Europe, where there are no climatic conditions for the existence of any steppe. This study is focused on the vegetational aspect of the pedogenesis of chernozems. We have examined three sorts of chernozems for their charcoal and pedological characteristics: the functional chernozems, the chernozems buried in Holocene material and the chernozems buried in Pleistocene material. The charcoal examination has proved the presence of woodland taxa in the areas of chernozems at different periods of time. The results of this study reveal that the high stability of soil organic matter has caused the persistence of chernozems in the areas with prevalent woodland vegetation.

CHERNOZEM. FROM CONCEPT TO CLASSIFICATION: A REVIEW

In this paper, we put together the most important facts that lead to the research on chernozem. Thanks to the work of V. V. Dokuchaev (1846–1903), chernozem stands at the forefront of pedology. In 1883, Dokuchaev introduced the first concept of chernozem: he defined chernozem as a steppe soil with pedogenesis dominated by a dry continental climate and steppe vegetation, with calcareous parent material. Chernozem is a soil well known for its high agronomical potential; therefore the perception of chernozem as something extraordinary valuable goes back far into history. Our review presents the key factors of the pedogenesis of chernozem by explaining the causes of the high stability of its organic matter and the role of vegetation and fauna in this process. Moreover, it shows that chernozem can have many aspects due to various (a) textures, (b) chemical compositions, (c) influence of water, (d) fauna, or (e) anthropogenic factors. We examine the position of chernozem in numerous national and international soil classifications over time. We have found out that chernozem had been classified, according to its properties, as a “steppe soil”, as a “calcic soil” or as an “isohumic soil”.

Are plant communities mainly determined by anthropogenic land cover along urban riparian corridors

Often used as a mitigation tool to landscape fragmentation, urban riparian corridors also suffered from the effects of the urban expansion. This study explored the relationships between plant riparian communities and two major environmental variables (land cover, soil characteristics) and analyzed the floristic change along an urbanization gradient. Fifteen sites were surveyed on both riverbanks of two riparian corridors characterized by contrasting water regimes in Strasbourg, North Eastern France. Data of spontaneous species abundance was collected from 180 quadrats using (i) all plant species, (ii) herbaceous stratum and (iii) ligneous stratum (bush and tree). The diversity and compositional patterns of riparian plant species were analyzed within each corridor according to three levels of urbanization (urban, suburban, peri-urban). Relationships between riparian communities, land cover and soil chemical properties (pH, nitrogen and carbon content, moisture) were established by between-class co-inertia analyses. Land cover emerged as the main factor explaining changes in riparian communities along the rural–urban gradient while soil chemical properties discriminate water stress and fluvial dynamics of the two corridors. Similar compositional patterns were found within the most urbanized sites with the establishment of ubiquitous species. The herbaceous stratum is best linked to the level of urbanization, whereas the tree stratum is primarily correlated with corridor attributes (hydrological regime, soil properties). Although riparian species and communities are mainly determined by land cover, urban riparian corridors maintain native biodiversity up to the urban center.

Factors responsible for Ixodes ricinus nymph abundance: Are soil features indicators of tick abundance in a French region where Lyme borreliosis is endemic?

In Europe, the hard tick Ixodes ricinus (Acari: Ixodidae) is the main vector of Lyme borreliosis spirochetes (Borrelia burgdorferi sensu lato group). A field study was conducted to evaluate the abundance of Ixodes nymphs in the French region of Alsace, where Lyme borreliosis is endemic, and to determine whether environmental factors such as soil moisture and composition may be associated with nymph abundance. In the ten sites studied, ticks were collected by drag sampling from March to October in 2013 and 2014. Temperature, relative humidity, saturation deficit, soil pH, humus composition and type of vegetation were recorded at each site. The abundance of I. ricinus was highly variable from one site to another. Inter-annual variations were also observed, since the nymph abundance were higher in 2013 than in 2014. This study shows that humus type can be indicative of nymph abundance. Three types of humus were observed: (1) moder, (2) mull, and (3) mull-moder humus. One of them, moder humus, which is characterized by a thick layer of fragmented leaves, was found in multivariate analyses to be strongly associated with the nymph abundance. This study demonstrates that factors such as saturation deficit do not suffice to explain the differences in nymph abundance among sites. The composition of the soil and especially the type of humus should also be taken into consideration when assessing acarological risk.

Stable calcium isotope speciation and calcium oxalate production within beech tree (Fagus sylvatica L.) organs

In this study, we linked Ca speciation with isotope composition in plants. To do this, we performed leachate experiments to access the soluble Ca, structurally bound Ca and insoluble Ca (i.e., water and weak acid resistant) within beech tree organs (Fagus sylvatica L.). Ca isotopic measurements were combined with infrared spectroscopy and calcium oxalate biomineralization identification. The results from our study indicate that bark and leaves are the most enriched in monohydrated calcium oxalate crystals (whewellite), which are observable in parenchyma and sclerenchyma tissues, whereas roots and wood are enriched in structurally bound Ca. Our leaching experiments also show decreasing δ44/40Ca isotopic signatures in the order of soluble Caxa0>xa0structurally bound Caxa0>xa0insoluble Ca. This finding implies that because leaves degrade faster than wooden organs and because Ca linked to pectate decomposes faster than Ca linked to oxalate crystals, differential Ca isotopic signatures are expected to be observed during litter degradation.