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We checked the effect of biochar addition to a fertile temperate soil on plant growth and the quantity and quality of seeds of four varieties of wheat (Triticumspp., two “ancient” varieties, Vernaand Senatore Cappelli, and two “modern” varieties, Bolognaand Claudio) and a high oleic hybrid of sunflower (Helianthus annuusL.). Relatively novel is the qualitative investigation of the marketable product, as few are the works on this topic. We tested three different doses of biochar—1, 4, and 20 t ha−1—versus an untreated soil (“control”) in a 2-year open field trial in Central Italy, where wheat was grown the first year and sunflower the second year. Biochar addition did not change the soil characteristics save for the carbon content, which increased significantly with the highest dose of biochar. Also, we did not find any significant biochar-induced effect on plant growth and yields of both wheat and sunflower. Regarding the qualitative aspects, adding biochar to the soil implied an increase in total polyphenols in the middlings and bran of wheat and, with the highest dose of biochar, also in total proteins and in flavonoids and caffeic acid derivatives. Instead, no difference in carotenoids concentration and antiradical activity was observed in middlings or bran. As for the sunflower, no significant difference in seeds’ composition was detected at any of the biochar doses. The addition of biochar to a fertile, well-drained soil as the one we investigated is not detrimental to the quantity and quality of wheat and sunflower seeds. Rather, the concentration of some polyphenols in wheat appears to be positively affected by biochar addition.

Wildfires are a driving factor of forest soils and their biota, especially in fire-prone ecosystems. Fire effects on soil microbial community are complex and still largely unknown. Greater knowledge is needed as fire frequency is expected to increase with human-induced climate change. This study aims at assessing the effects of a single moderately severe wildfire on microbial community diversity and activity in a Mediterranean forest soil by DNA molecular screening (polymerase chain reaction–denaturing gradient gel electrophoresis). For this purpose, the soil of a burned area was sampled 3 days and 10 months after the fire and compared with the soil of an unburned contiguous area. For the DNA fingerprinting, we analyzed both extracellular and intracellular DNA fractions of the soil metagenome. The fire impact on soil was also rated in terms of selected enzyme activities, as reliable bioindicators of biogeochemical cycles. An immediate fire-induced general decrease in enzyme activities and more durable changes in the bacterial and fungal communities structure were found, although microbial biomass was not significantly affected. Litter layer was completely turned to char and ash by the fire, but after 10 months, it showed a fair amount of DNA, a structured microbial community, and a good enzymatic activity. Overall, such relatively fast recovery was likely caused by the microbial biomass that survived the fire, which evidently adapted to the new soil conditions.

Wildfires are a driving factor of forest soils and their biota, especially in fire-prone ecosystems. Fire effects on soil microbial community are complex and still largely unknown. Greater knowledge is needed as fire frequency is expected to increase with human-induced climate change. This study aims at assessing the effects of a single moderately severe wildfire on microbial community diversity and activity in a Mediterranean forest soil by DNA molecular screening (polymerase chain reaction-denaturing gradient gel electrophoresis). For this purpose, the soil of a burned area was sampled 3 days and 10 months after the fire and compared with the soil of an unburned contiguous area. For the DNA fingerprinting, we analyzed both extracellular and intracellular DNA fractions of the soil metagenome. The fire impact on soil was also rated in terms of selected enzyme activities, as reliable bioindicators of biogeochemical cycles. An immediate fire-induced general decrease in enzyme activities and more durable changes in the bacterial and fungal communities structure were found, although microbial biomass was not significantly affected. Litter layer was completely turned to char and ash by the fire, but after 10 months, it showed a fair amount of DNA, a structured microbial community, and a good enzymatic activity. Overall, such relatively fast recovery was likely caused by the microbial biomass that survived the fire, which evidently adapted to the new soil conditions. [ABSTRACT FROM AUTHOR]

Scientists are actively debating whether the Anthropocene, the geologic time span (GTS) we are now living in, should be considered a period, epoch, or age in the geologic timescale. The solution is not easy, because the beginning of this GTS is undefined and the end unknown. In fact, there is no agreement on when the Anthropocene began, the proposed dates ranging from the Second World War, when radioactive fallout branded soils and sediments all over the world, to little after the end of the last glacial period, i.e. 11.7 thousand years ago, therefore coinciding with the onset of the Holocene. We are in favour of a concurrence of the Anthropocene with the Holocene, although a major impact of people on the environment began diachronically in different parts of the world. This single GTS should be named Anthropocene because it is chiefly characterized by a peculiar process of change for the planet: human impact. Nevertheless, a pivotal hindrance for the Anthropocene to be worthy of a formal geologic definition remains. The Anthropocene is open ended, therefore its real duration is unknown.

Land use change is one of the anthropogenic interventions that may induce substantial modifications to both the quantity and quality of soil organic matter (SOM). Soils from three cultivated areas (two types of rainfed upland and one irrigated lowland) and two forests (subtropical managed and temperate unmanaged) in a midhill watershed of Nepal were studied to assess the effect of land use change on SOM quality. Bulk SOM was analyzed using solid‐state 13C nuclear magnetic resonance (NMR) and fractionated by acid hydrolysis into pools with different chemical composition and, thus, different tendencies to decomposition. The NMR analysis showed a clear prevalence of O‐alkyl C over alkyl C and aromatic C, with major differences between both soils and two depth intervals of the same soil (0–20 and 20–40 cm). Acid hydrolysis revealed that the labile C pool is larger in the 0‐ to 20‐ than the 20‐ to 40‐cm soil depth of each land use. Labile C was larger in the temperate unmanaged forest and the irrigated cultivated land than in the other soils at both soil depths. Of the cultivated rainfed soils, the recently reclaimed soil contained less labile C than the historically cultivated soil, while the labile C in the irrigated soil exceeded that in both rainfed soils. The results suggest that changes in land use from forest to cultivation and the irrigation of the cultivated land may significantly affect not only the quantity but also the quality of the SOM and, more importantly, its chemical recalcitrance to degradation. As a consequence, any future decisions regarding land management in the fragile mountain areas of Nepal should be carefully considered with respect to the nature of the SOM.

Abstract: Fungal activity is thought to play a direct and effective role in the breakdown and dissolution of primary minerals and in the synthesis of clay minerals in soil environments, with important consequences for plant growth and ecosystem functioning. We have studied primary mineral weathering in volcanic soils developed on trachydacite in southern Tuscany using a combination of qualitative and quantitative mineralogical and microbiological techniques. Specifically, we characterized the weathering and microbiological colonization of the magnetically separated ferromagnesian minerals (biotite and orthopyroxene) and non-ferromagnesian constituents (K-feldspar and volcanic glass) of the coarse sand fraction (250–1,000 µm). Our results show that in the basal horizons of the soils, the ferromagnesian minerals are much more intensively colonized by microorganisms than K-feldspar and glass, but that the composition of the microbial communities living on the two mineral fractions is similar. Moreover, X-ray diffraction, optical and scanning electron microscope observations show that although the ferromagnesian minerals are preferentially associated with an embryonic form of the clay mineral halloysite, they are still relatively fresh. We interpret our results as indicating that in this instance microbial activity, and particularly fungal activity, has not been an effective agent of mineral weathering, that the association with clay minerals is indirect, and that fungal weathering of primary minerals may not be as important a source of plant nutrients as previously claimed.

The umbric epipedon is a diagnostic surface horizon recognized by both the World Reference Base for Soil Resources and the U.S. Soil Taxonomy. It is mainly characterized by a dark color, a moderate to high content of OM, and a base saturation of less than 50%. In the N Apennines, Central Italy, forest soils over 600–700 m a.s.l. often have this epipedon. This paper stresses the morphological, chemical, and biological properties of the epipedon, specifically in the Vallombrosa Forest, where considerable work has been done in the last decade. Here, the umbric epipedon forms on sandstone, in high forests of Abies alba, Fagus sylvatica, and Castanea sativa. It does not have homogeneous properties throughout its thickness and often is divided into two distinct genetic horizons, A1 and A2. The A1 horizon is thinner, darker, and richer in OM, more base-saturated, and biologically more active than the underlying A2 horizon. The mean residence time of the bulk OM amounts to about a century in the A1 horizon, versus half a millennium in the A2. In both A1 and A2 horizons, the non-humic fraction prevails in the OM; this could account for the high susceptibility of the umbric epipedon to degrade when the forest is clear-cut or undergoes extensive uprooting due to windstorms or heavy snow loads. Significant discrepancies between the two A horizons have been found in regard to the microbial community. Umbric epipedons which developed under different tree species show minor differences, mainly concerning the microbial community.

The brittleness of fragipans is generally ascribed to the close‐packing fabric arrangement acquired at the initial step of pedogenesis thanks to physical processes. However, there is an on‐going debate over the agent causing soil densification. In this work, we tested the plausibility that ice segregation or liquefaction could have been the cause of the compaction of four fragipans. Two of them are located in nonseismic areas that have experienced periglacial conditions; one is from a strongly seismic area not affected by periglacial conditions, while the fourth site underwent moderate seismic activity and slight periglacial conditions. After disaggregation in the laboratory, soil specimens were submitted to freeze–thaw cycles and vibrations at different amplitude and duration, either dry or water‐saturated. Analyses of aggregate stability, bulk density, porosity, and pore‐size distribution were made on natural and treated specimens. Results indicated that the compactness arose mainly from the close‐packing arrangement of particles. The freeze–thaw cycles were able to reproduce only some of the features in the water‐saturated specimens, independent of whether they came from periglacial or seismic areas, while those from seismic areas successfully acquired the original arrangement after vibrations‐induced liquefaction. This different behavior could be partly explained by the fact that consolidation after liquefaction occurs only if a material with proper particle‐size distribution and mineralogical assemblage is saturated by solutions able to disperse phyllosilicates and promote their face‐to‐face arrangement. Our findings support the hypothesis that liquefaction of soil material due to earthquakes could indeed provide a dense parent material in which the fragipan may develop through pedogenesis.

Abstract The carbon dioxide efflux to the atmosphere and the concentrations at various depths in two soils were measured, for more than a year, under pure stands of silver fir ( Abies alba Mill.) and European beech ( Fagus sylvatica L.) in central Italy. Microbial biomass and activity at the monitored depths were determined in the laboratory and the CO₂ evolved from incubated samples was submitted to radiocarbon analysis to assess the mean residence time of the organic matter degraded by microorganisms. The CO₂ efflux showed similar trends in the two soils, with highest values in October and lowest in January. The efflux depended more on air and soil temperatures than soil moisture, and was related to these variables better under fir than under beech. In both soils, the CO₂ concentration increased with depth: in the top horizon it was low and similar to that of the atmosphere, while in the deeper horizons it often amounted to considerable values (up to more than 1% by volume in the BC horizon under fir). The subsoil of the fir stand generally showed much higher CO₂ concentrations than that of the beech. The basal respiration as determined in the laboratory was at a maximum in the topsoil and decreased sharply downwards. Therefore, the high CO₂ concentrations measured in the field at the bottom of the profiles--where roots were few, and microbial biomass and available C pool were at a minimum--appeared to be due more to slow diffusivity of the soil matrix rather than to heavy release of the gas by the biota. The organic matter respired by microorganisms in incubated soil samples showed positive values of Δ¹⁴C that revealed a recent synthesis. The estimated mean residence time increased with depth, suggesting a generally higher degree of stabilisation of the organic pool in the subsoil.

Rock fragments (particles > 2 mm) are usually considered chemically inert for plant growth. In this paper, the potential fertility in terms of exchangeable Ca, Mg, and K of rock fragments from sandstone and siltstone derived soils from northern Apennines (Italy) is reported and contrasted with that of the fine earth (particles < 2 mm). The results show that rock fragments are a source of Ca, Mg, and K. When expressed on a volume basis, the abundance of these exchangeable nutrients sometimes may equal or surpass that of the fine earth. The plant uptake of Mg and K has been demonstrated in growth experiments with Agrostis under controlled conditions.

Summary: With regard to the high mortality of silver fir (Abies alba Mill.) in Italy, pathological and climatic causes are considered crucial, while soil properties are usually neglected. Two of the largest Tuscan forests of this species, the one of Vallombrosa and the other of Mount Amiata, are seriously affected byHeter obasidion annosum, a fungus causing root rot. However, in spite of the same provenance of firs and intersterile group of the fungus, the tree death is different at the two sites. In one case, firs quickly died standing, while in the other they were uprooted after a slow course of the illness. A study was conducted on the two localities to perceive the role of soil properties in this connection. In the light of our results, pedological conditions are important, negatively affecting the plants either “directly” — limiting deep rooting and preventing the trees to achieve sufficient anchorage in the ground — and “indirectly” — favouring the spread and the virulence ofH. annosum.

Low-molecular-weight organic acids (LMWOA's) play an important role in soil genesis and plant physiology. Oxalic acid is one of the more common and abundant LMWOA's in forest soils, where it accumulates especially as salts of Ca. In two soils under silver fir (Abies alba Mill.) from Tuscany, Italy, we measured the oxalate concentration of the entire profile. Oxalate was present up to two metres depth, but accumulates preferentially in the upper horizons. We determined also the bulk density of the fine earth, and organic carbon and available phosphorus. In one of the two soils, the oxalate concentration along the profile was regressed negatively with depth and bulk density, and positively with organic C and available P.

The nitrogen content of humic and fulvic acid fractions recovered in parallel with sodium hydroxide and a mixture of sodium hydroxide and sodium pyrophosphate from a volcanic soil under pine was determined. Despite minor differences for some horizons, the values found by the two methods were similar. Furthermore, the ratio between the N contents in the humic and fulvic acid fractions (Nh : Nf) was independent of the nature of the extractant. This fact and the facility of the determination suggest investigating if the Nh: Nf ratio can be used as indicator for the quality of soil organic matter.