Eleonora Bonifacio

Pedogenic chlorites in podzolic soils with different intensities of hydromorphism: Origin, properties, and conditions of their formation

Minerals of the pedogenic chlorite group were studied in the clay fractions isolated from the mineral horizons of podzolic and gleyic peat-podzolic soils. In the AE and E horizons of the podzolic soil, pedogenic chlorites are thought to develop from vermiculite, whereas in the E horizon of the gleyic peat-podzolic soil, they can be formed from smectite minerals. For estimating the degree of chloritization (the degree of filling of the interlayer space of 2: 1 minerals with Al hydroxides), a numerical criterion was is proposed. The difference between the values of this criterion before and after the treatment of the preparations with NH4F indicated that the degree of chloritization in the pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the AE horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil. Another numerical criterion was proposed to estimate the degree of polymerization of Al-hydroxy complexes in pedogenic chlorites. This criterion was based on the thermal stability of soil chlorites and represented the temperature at which an increase in the intensity of the 1.0-nm peak after heating the K-saturated preparations exceeds 50% of its initial value. According to this criterion, the degree of polymerization of the Al-hydroxy interlayers in pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil ≥ the AE horizon of the podzolic soil. The distinct interrelation between the soil properties and the degrees of chloritization and polymerization of the Al-hydroxy interlayers attests to the modern origin of the pedogenic chlorites.

Effects of different Kalahari-desert VA mycorrhizal communities on mineral acquisition and depletion from the soil by host plants

Abstract Seedlings of Vangueria infausta, an indigenous Kalahari tree, were used as plant symbionts in a pot experiment designed to measure the effect of three local vesicular–arbuscular mycorrhizal (VAM) fungal communities on mineral acquisition and concentrations in host shoots. VAM significantly affected seedlings size. The highest level of VAM mycorrhizae occurred in soil with intermediate P concentration. Two VAM communities had the highest mycorrhizal response in their soils of origin. The presence of VAM caused a significant depletion of P from soils. VAM communities differed in their ability to promote P, Ca and N uptake. A significant interaction between VAM community and soil type—in terms of Ca and N concentration in shoots—indicates a local adaptation of the VAM species.

Chemical and spectroscopic characteristics of humic acids and dissolved organic matter along two Alfisol profiles.

The aim of this study was to elucidate the heterogeneous structural and functional composition of humic acids (HAs) and dissolved organic matter (DOM) isolated from two Alfisol profiles with different soil texture, in order to develop a better understanding of the organic matter dynamics. Soil samples were collected at different depths from three (Ap, 2AB and 2Bt) and eight (A1, A2, A3, E1, E2, 2Bt1, 2Bt2 and 2Bt3) soil horizons of two Alfisols located in the south (PR1) and north (PR2) of Italy, with a clay texture and a silt loam to loam ones, respectively. Chemical and spectroscopic methods were used to characterize the HAs and the DOM isolated from different soil horizons, including Ultraviolet-Visible (UV-Vis), Fourier Transform Infrared (FTIR), and Fluorescence spectroscopies. The HAs and the DOM isolated from the two Alfisols apparently showed significant differences in their compositional, structural and functional characteristics. In particular, the HAs isolated from the PR1 featured a higher degree of humification and molecular complexity with respect to those isolated from the PR2. On the contrary, the DOM samples isolated from the PR2 showed a more marked aromatic character and polycondensation degree. Both the HAs and the DOM obtained from the PR1 presented a greater qualitative homogeneity with respect to those obtained from the PR2. These results could be reasonably ascribed to the different texture and horizons of the two Alfisols, and to a greater pedogenesis occurred in the PR1.

Soil properties under Norway spruce differ in spruce dominated and mixed broadleaf forests of the Southern Taiga

In natural forest, disturbance changes tree species composition which in turn affects soil properties. Two areas in the Central Forest State Biosphere Reserve, in the Russian Southern Taiga Zone, differed in the intensity of disturbance: Norway spruce was the dominant species at one site, while at the other spruce was mixed with broadleaves. The presence of broadleaves was due to large gaps in the canopy having been formed, which have triggered vegetation succession. At both sites, five plots were selected to evaluate how the presence of broadleaves influences the properties of the soils under spruce. Soil samples were taken close to spruce trees and the O, A and E horizons were analysed. A difference in the distribution of organic matter in the soil horizons was evident, with a higher concentration in the O and A horizons at the spruce dominated site, while a more homogeneous distribution was found under spruce at the site where broadleaves were abundant. The organic matter did not only differ in quantity, but also in quality as estimated by the C/N ratio, and therefore affected the CEC and element relative availability. No differences at the two sites were found for water-extractable and exchangeable elements, but the ratio between the exchangeable and the acid-extractable forms were different, suggesting a higher relative availability of the elements at the spruce dominated site, and thus potentially higher leaching. Both theoretical and empirical studies have suggested that podzolisation and accumulation of organic matter in the O horizon are related to stagnation of ecosystem processes and ecosystem decline. Our data suggest that the presence to windthrow sites and the inclusion of broadleaf species acts to slow or even reverse podzolisation even in spruce dominated sites.

Characteristics of soil organic matter in a limnic histosol of the alpine morainic system

Histosols represent a large carbon reservoir and their preservation is important to limit the emission of CO2 and the related ecological consequences. In these soils, C storage is governed by waterlogging, bacterial activity, and type of vegetation from which soil organic matter (SOM) originated. In limnic peats, moreover, calcium could play some roles on SOM dynamics. The characteristics of organic fractions composing a Limnic Histosol subjected to intermittent periods of oxidation have been studied to understand the main factors influencing SOM dynamics and accumulation. Soil organic matter was constituted mainly by the unextractable fraction (88.0% of organic C). Dissolved organic matter was in low concentrations (1.30%), formed mainly by undecomposed labile material. Fulvic and humic acids (HAs) were highly humified and rich in O-containing groups, probably because of the periodic oxidizing conditions. Humic acids (concentration, 5.38%), further fractionated by dialysis in three fractions on a molecular weight basis, were constituted mainly by the heaviest fraction (greater than 50 kDa; concentration, 5.36%). Humin was composed of a hydrophobic fraction, derived probably from lipids and waxes, and of a hydrophilic fraction, with features closer to those of HA. Both fractions contained surprisingly large amounts of carboxyl and phenolic groups and trapped a large percentage of Ca, which is unextractable even after strong acid treatments. This suggests that humin was actually formed by smaller molecules that strongly interact with Ca through their polar groups, forming larger aggregates. The large percentage of unextractable organic material and the strong interaction with Ca could preserve SOM from microbial degradation and, hence, limit the mineralization even in the absence of water, preserving a C sink that is presently storing a large amount of C in both organic and carbonate forms.

Influence of serpentine abundance on the vertical distribution of available elements in soils

Background and AimBiotic and abiotic factors contribute in shaping the distribution through the soil profile of elements released by mineral weathering; among them, leaching and biocycling dominate in temperate environments. We evaluated if the intensity of leaching and biocycling of nutrients can be modulated by element deficiencies linked to the abundance of serpentine in the soil parent material, i.e. if the most deficient elements are more efficiently retained.MethodsWe selected twelve poorly developed soils from Northern Italian beech stands, with variable amounts of serpentinites in the parent material, and determined total and exchangeable Ca, Mg and K, as well as an index of abundance of serpentine minerals.ResultsThe total element content depended on the abundance of serpentines, while only exchangeable Mg was related to the parent material. The vertical trend of Ca and K indicated the role of biocycling in all soils, but the relative availability of Ca (ratio between exchangeable and total content) was much higher in the top horizons of serpentine-rich soils.ConclusionsThe different element availability among soils suggested that the vertical distribution of available elements was linked to the parent material and that losses were limited in serpentine-rich soils, probably because plants take up the deficient elements as soon as they are released from litter and thus limit their leaching in deeper soil horizons.

Destabilization of aggregates in some typic fragiudalfs

Several mechanisms are responsible of the destabilization of soil aggregates in water: slaking, swelling, and dispersion of the clay and mechanical breakdown by abrasion. The aggregate resistance differs in relation to the dominant disruptive phenomenon, and by applying different methods to assess aggregate stability, a specific physical susceptibility of different horizons may be evidenced. Therefore, we evaluated the relative importance of the mechanisms of breakdown in some Typic Fragiudalfs, taking into account the specific horizon characteristics, to understand if the fragipan brittleness is related to a specific mechanism, and how the soil properties affect the resistance to fast wetting. The standard wet sieving test, which evaluates all destabilization mechanisms together, indicated a clear role of soil organic matter in protecting the aggregates, with greater losses in the deeper horizons (about 70%), but did not allow us to discriminate between fragipans and other horizons. When the losses caused by water abrasion were separated from the breakdown due to wetting phase using a kinetic approach, a high breakdown caused by fast wetting was found in deep horizons, but still no difference between fragipan and non-fragipans were visible, even though fragipan clods are known to be particularly sensitive to fast wetting. By excluding the effect of organic matter and prewetting the samples with ethanol, differences between these horizons appeared within the water saturation phase and fragipans and non-fragipans were found to be sensitive to different mechanisms. In fragipans, the relative percentage of slaking was higher, always above 30%, whereas for non-fragipans clay dispersion and swelling weighted more heavily. The complexity of the clay fraction did not allow us to relate the mineralogy to swelling or dispersion, but slaking was instead clearly related to clay arrangement and the consequent porosity characteristics (r2 = 0.62), and not to clay content only.

Alien red oak affects soil organic matter cycling and nutrient availability in low-fertility well-developed soils.

Background and aimsInvasive alien species can dramatically change the litter and organic matter decomposition rate, nutrient cycling and availability, thus threatening the ecosystem functionality. We assessed the effect of red oak (QR) introduction on low fertility well-developed soils, originally covered by Quercus robur L. (QC).MethodsWe determined litter and soil organic matter composition and decomposition rate by combining morphological features with 13C NMR spectroscopy, NaClO oxidation and soil respiration. Total and available nutrients were also determined.ResultsThe sites showed different humus forms: Dysmull-Hemimoder in QC and Mor in QR. The Oi horizons had a similar composition, but the higher presence of tannins and alkyl C/O − alkyl C and aryl C/O − alkyl C ratios in QR indicated that litter was less degradable. This was confirmed by soil respiration tests, with a higher preservation of the NaClO resistant fraction along the profile, mainly due to selective accumulation of alkyl components. This was accompanied by high retention of phosphorus in the organic horizons and drastic reduction of both total and available P in the mineral horizons. Calcium was strongly affected too.ConclusionsIn these well-developed soils red oak changed organic matter dynamics, reduced P availability and cation biocycling, leading the ecosystem functionality towards a no-return threshold.

Early stages of soil development on serpentinite: the proglacial area of the Verra Grande Glacier, Western Italian Alps

PurposeClimate change is driving strong variations in mountain habitats, such as glacier retreat, which is releasing large surfaces soon colonized by vegetation and attacked by weathering and pedogenesis. Many proglacial soil chronosequences have been studied in different parts of the world, but no study is available on early soil development and pedogenesis on serpentinite.Materials and methodsWe analysed the development of the main chemical (pH, organic matter, nutrients and exchangeable cations) and morphological properties in three soil chronosequences in the Verra Grande Glacier forefield (Italian side of the Monte Rosa Group, Western Alps), characterized by slightly different parent materials (pure serpentinite or serpentinite with small gneiss inclusions) and topography (steep lateral moraines or flat basal till).Results and discussionOrganic matter accumulation, acidification and base and metal leaching are the most important pedogenetic processes active during early stages of soil formation on serpentinite in the upper subalpine altitudinal belt. These processes are associated with minor changes in color and structure showing weak mineral weathering. Biocycling of nutrients is limited on pure serpentinite because of weak primary productivity of the plant community. Pedogenesis is quite slow throughout the forefield, and it is slowest on pure serpentinite. On flat surfaces, where slow erosion permits a fast colonization by Ericaceae, the podzolization process begins after few centuries since moraine deposition, while on steep slopes more time is required.ConclusionsPedogenesis on serpentinite is extremely slow. The fast colonization by grassland species increases the speed of pedogenetic trends where serpentinitic till is enriched by small quantities of P-rich gneiss. The encroachment of forest-shrub species increases the speed of pedogenetic trends thanks to a strong nutrient biocycling.

Wet Aggregate Stability of Some Botswana Soil Profiles

ABSTRACT During intense and short rainfall events, important losses of fertility are expected as a result of erosion in drylands because the nutrient pools are concentrated in the topsoil. Therefore, we evaluated the kinetics of aggregate stability in some Haplargids and Torripsamments in Botswana as it represents a resistance factor against losses of materials, measuring also the release of organic matter and phosphorus during wet sieving. We found very low contents of 1–2 mm aggregates in both soil types—although the Haplargids had higher levels of this size aggregate (19%) compared with the Torripsamments (10%)—and no differences between the topsoil and the deeper horizons. The total losses of aggregates were similar in topsoils and deep soil horizons and independent from soil order, but the Entisols had a greater proportion of aggregate breakdown, 38% on the average, when the sample was water-saturated. Only clay and silt content, and cation exchange capacity showed good correlations with aggregate stability. Organic matter or iron oxides had no effect, suggesting that aggregation is the result of cation bridging between mineral particles. Up to 97% of the organic matter released into water was lost at the beginning of the wet sieving, but the amounts were not related to aggregate breakdown, indicating that organic matter, besides not influencing the stability of macroaggregates, had little effect on the stabilization of microaggregates. Phosphorus was also released during the wet sieving, and was related to soil available P (r = 0.713 after 5 min). With no effect of organic matter on aggregate stability, and nutrients concentrated in the topsoil, the vulnerability of these soils to fertility losses is therefore extremely high.