Snowbeds are more affected than other subalpine-alpine plant communities by climate change in the Swiss Alps

While the upward shift of plant species has been observed on many alpine and nival summits, the reaction of the subalpine and lower alpine plant communities to the current warming and lower snow precipitation has been little investigated so far. To this aim, 63 old, exhaustive plant inventories, distributed along a subalpine-alpine elevation gradient of the Swiss Alps and covering different plant community types (acidic and calcareous grasslands; windy ridges; snowbeds), were revisited after 25 to 50-years. Old and recent inventories were compared in terms of species diversity with Simpson diversity and Bray-Curtis dissimilarity indices, and in terms of community composition with Principal Component Analysis. Changes in ecological conditions were inferred from the ecological indicator values. The alpha-diversity increased in every plant community, likely because of the arrival of new species. As observed on mountain summits, the new species led to a homogenisation of community compositions. The grasslands were quite stable in terms of species composition, whatever the bedrock type. Indeed, the newly arrived species were part of the typical species pool of the colonised community. In contrast, snowbed communities showed pronounced vegetation changes and a clear shift towards dryer conditions and shorter snow cover, evidenced by their colonisation by species from surrounding grasslands. Longer growing seasons allow alpine grassland species, which are taller and hence more competitive, to colonise the snowbeds. This study showed that subalpine-alpine plant communities reacted differently to the on-going climate changes. Lower snow/rain ratio and longer growing seasons seem to have a higher impact than warming, at least on plant communities dependent on long snow cover. Consequently, they are the most vulnerable to climate change and their persistence in the near future is seriously threatened. Subalpine and alpine grasslands are more stable and, until now, they do not seem to be affected by a warmer climate

Decoupling of topsoil and subsoil controls on organic matter dynamics in the Swiss Alps

Our understanding of mechanisms governing soil organic matter (OM) stability is evolving. It is gradually becoming accepted that soil OM stability is not primarily regulated by the molecular structure of plant inputs, but instead by the biotic and abiotic properties of the edaphic environment. Moreover, several experimental studies conducted in artificial systems have suggested that mechanisms regulating OM stability may differ with depth in the soil profile. Up to now however, there is very limited field-scale evidence regarding the hierarchy of controls on soil OM dynamics and their changes with soil depth. In this study, we take advantage of the high heterogeneity of ecological conditions occurring in the alpine belt to identify the major determinants of OM dynamics and how their significance varies with depth in the soil profile. Aboveground litter, mineral topsoil, and subsoil samples originating from 46 soil profiles spanning a wide range of soil and vegetation types were analysed. We used Rock-Eval pyrolysis, a technique that investigates the thermal stability of OM, as an indicator of OM dynamics. Our results show a clear divergence in predictors of OM thermal stability in the litter, topsoil, and subsoil layers. The composition of OM correlated with its thermal stability in the litter layer but not in mineral soil horizons, where the supply rate of fresh organic material and the physical and chemical characteristics of the pedogenic environment appeared important instead. This study offers direct confirmation that soil OM dynamics are influenced by different ecosystem properties in each soil layer. This has important implications for our understanding of carbon cycling in soils under a changing climate

Humusica 1, article 7: Terrestrial humus systems and forms – Field practice and sampling problems

The present paper should be read after the six preceding articles dealing with fundamental concepts, vocabulary, principles and keys of our morpho-functional classification of humus systems and forms, the whole book being conceived as a guide for field studies. It now concerns seven questions which may arise when passing from knowledge to practice or, in other terms, from concepts to real things. In the field, humipedons can differ from reported photographs. Trees, bushes and/or herbs interfere with soil functioning and may generate different humipedons even over a relatively small surface. More generally a researcher must select a few unit plots re- presentative of a given natural floor for defining the frame of his investigation. In this article, authors present some practical and theoretical landmarks and illustrate some solutions for studying humipedons in common natural sites, and replacing them within ecosystem dynamics

HIV-1 inhibiting activity of the essential oil and different fractions of Ridolfia segetum (L.) Moris

The essential oil of Ridolfia segetum (L.) Moris collected in Sardinia (Italy) has been fractionated and assayed on the two enzymatic associated activities of the HIV-1 reverse transcriptase (RT): the RNA-dependent DNA polymerase (RDDP) and the ribonuclease H (RNase-H) activities. The R. segetum oil inhibited the HIV-1 RT RDDP associated activity in a dose dependent manner showing an IC50 value of 0.094 mg/ml , while it was inactive on the RNase-H associated activity. Nevirapine was used as a positive control. Three main fractions (RS1, RS2, and RS3) were obtained from R. segetum essential oil fractionation, representing 79%, 7%, and 2%, respectively, of the total oil. The most potent fraction was RS2, containing dillapiol, myristicin and piperitenone oxide, followed by RS3 and RS1. Because these data might fit with the presence of dillapiol in the fractions, we hypothesized that this compound could exert inhibitory activity. Fraction RS2 was refractionated to obtain a mixture of dillapiol and myristicin accounting of 3,14 %of the total oil (RS-Ag). The RS‑Ag fraction was also active toward RDDP activity. Furthermore, purified dillapiol and myristicin were tested on RDDP activity and were found to inhibit it with IC50 values of 0.69 and 4.5 mg/mL, respectively. It is worth noting that both RS2 and RS‑Ag were roughly 5- to 6-fold more active than the pure dillapiol itself. A possible explanation for this finding is that dillapiol and myristicin could act synergistically on HIV-1 RT RDDP activity

A sesterpene lactone from Artemisia umbelliformis Lam.

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A sesterterpene lactone from Artemisia umbelliformis Lam.

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