Anna Andreetta

Microbial dynamics in Mediterranean Moder humus

There is a growing interest in the links between humus forms and soil biota, and little is known about these links in Mediterranean ecosystems. Culture-independent techniques, such as DNA extraction followed by DGGE and enzyme activities, allowed us to compare microbial communities in two horizons of a forest soil in different seasonal conditions. Direct in situ lysis was applied for extraction of DNA from soil; intracellular DNA was separated from extracellular and used to represent the composition of microflora. The aims were to describe how biochemical and microbiological parameters correlate with topsoil properties in typical Mediterranean Moder humus. Changes in bacterial and fungal community composition were evident from DGGE profiles. Degrees of similarity and clustering correlation coefficients showed that the seasonal conditions may affect the composition and activity of bacterial and fungal communities in the OH horizon, while in the E horizon the two communities were hardly modified. In the same season, OH and E horizons showed a different composition of bacterial and fungal communities and different enzyme activities, suggesting similar behaviour of eubacteria and fungi relatively to all the variables analysed. Evidently, different organic carbon content in soil horizons influenced microflora composition and microbial activities involved in the P and N cycles.

Biological and physico-chemical processes influence cutin and suberin biomarker distribution in two Mediterranean forest soil profiles

Recent investigations have shown macromolecules, such as cutins, and suberins as effective markers for above and belowground plant tissues. These biopolyesters contain structural units specific for different litter components and for root biomass. The aim of this work was to understand the fate of plant organic matter (OM) in Mediterranean forest soils by evaluating the incorporation of cutin and suberin by measuring specific biomarkers. Soil and plant tissue (leaves, woods and roots) samples were collected in two mixed Mediterranean forests of Quercus ilex (holm oak) in costal stands in Tuscany (central Italy), which have different ecological and edaphic features. Ester-bound lipids of mineral and organic horizons and the overlying vegetation were analysed using the saponification method in order to depolymerise cutins and suberins and release their specific structural units. Cutin and suberin specific aliphatic monomers were identified and quantified by gas chromatographic techniques. The distribution of cutin and suberin specific monomers in plant tissue suggested that mid-chain hydroxy acids can be used as leaf-specific markers and α,ω-alkanedioic acids and ωC18:1 as root-specific markers. Differences in the distributions of biomarkers specific for above and belowground plant-derived OM was observed in the two types of soils, suggesting contrasted degradation, stabilisation and transport mechanisms that may be related to soil physico-chemical properties. The acidic and dry soil appeared to inhibit microbial activity, favouring stabilization of leaf-derived compounds, while, in the more fertile soil, protection within aggregates appeared to better preserve root-derived compounds.

Integrating sedimentological and palaeopedological data for palaeoenvironmental reconstruction: examples from the Plio-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy)

The study of palaeosols, coupled with the classical methods of process sedimentology, is increasingly becoming a powerful tool for palaeoenvironmental reconstructions. The intrinsic complementarity of these two methods, which record the effects of processes developing over different periods of time, allows to improve the detail of facies analysis. This type of approach has actually never been adopted for the Upper Valdarno Basin, which is one of the best-known continental Plio-Pleistocene basins of the Northern Apennines. The aim of this paper is to document the existence of pedogenized intervals within the Upper Valdarno basin fill and to describe and characterize them in terms of sedimentary and pedogenic processes. Thus we tested this approach on four stratigraphic intervals, selected within the whole succession because of their particular significance in the basin history. Deposits have been described and interpreted in terms of sedimentary facies and pedologic characteristics, with particular attention on the inferred relative temporal relationships between sedimentary and pedogenic processes. This led to several considerations about landscape stability and evolution, accommodation and sedimentation rates, which are not commonly possible with the analysis of single-event deposits.