Soil Granulometry Research Articles

Growth Forms and Functional Guilds Distribution of Soil Fungi in Coastal Versus Inland Sites of Victoria Land, Antarctica.

Simple SummaryAntarctica represents one of the most limiting environments on Earth, where exposed soils, transiently present on coastal areas and permanently exposed on McMurdo Dry Valleys, are one of the few substrata supporting microbial communities. Within these communities, fungi are one of the dominant components and play pivotal roles in recycling the extremely limited organic matter available. Despite their astonishing adaptations, the diversity of these communities and the factors determining their resistance are still poorly known. In this optic, this study aimed to give insights in the environmental parameters determining the structure of these communities and their adaptive strategies, in terms of growth forms and lifestyles. We found that abiotic conditions were the main drivers of well differentiated communities. Additionally, we highlighted that most species seemed to be highly adapted to this habitat, which may result in a relatively low resilience ability to changes in environmental condition. Both these results are of particular concern in light of global warming. Even minimal changes to environmental conditions may dramatically alter the Antarctic soil communities, risking the disappearance of many species still undescribed.In Victoria Land, Antarctica, ice-free areas are restricted to coastal regions and dominate the landscape of the McMurdo Dry Valleys. These two environments are subjected to different pressures that determine the establishment of highly adapted fungal communities. Within the kingdom of fungi, filamentous, yeasts and meristematic/microcolonial growth forms on one side and different lifestyles on the other side may be considered adaptive strategies of particular interest in the frame of Antarctic constraints. In this optic, soil fungal communities from both coastal and Dry Valleys sites, already characterized thorough ITS1 metabarcoding sequencing, have been compared to determine the different distribution of phyla, growth forms, and lifestyles. Though we did not find significant differences in the richness between the two environments, the communities were highly differentiated and Dry Valleys sites had a higher evenness compared to coastal ones. Additionally, the distribution of different growth forms and lifestyles were well differentiated, and their diversity and composition were likely influenced by soil abiotic parameters, among which soil granulometry, pH, P, and C contents were the potential main determinants.

Could soil granulometry and permeability drive the occurrence of the dune-dwelling ants from the genus Mycetophylax?

Species distribution can be influenced by several biotic and abiotic factors. Physical soil properties, such as granulometry and permeability, can, therefore, be key determinant factors of the occurrence of ground-dwelling species. Here, we evaluate whether the physical properties of soil, such as granulometry and the resulting soil permeability, could drive nesting occurrence of the endemic psammophilous ants from the genus Mycetophylax and, in turn, their distribution. To accomplish this goal, we tested the hypothesis that variations in the granulometry and the resulting permeability (high or low D10 values) of beach soils contribute to explain the distribution pattern of dune endemic species from the genus Mycetophylax. We sampled sand soils from 26 beaches across the known distribution of the species along the Brazilian Atlantic coast. Sorting through seven mesh sieves, we determined the proportion of sand grain size of each sample and then calculated the effective diameter (D10). Therefore, we investigated the occurrence of the three ant species in relation to the soil permeability determined by D10. The spatial variation in sand grain size and its permeability across the beaches of the Atlantic coast is likely one of the contributors that influence the pattern of distribution of psammophilous ants such as Mycetophylax simplex, M. conformis, and M. morschi.

Fungal diversity and functionality are driven by soil texture in Taylor Valley, Antarctica

The McMurdo Dry Valleys surface is mainly constituted from unconsolidated permafrost. Despite the combination of cold and dry conditions, transiently wetted soils close to lake edges are hotspots of intense biological activity, that can support the surrounding soil ecosystems in such extreme environments. These soils host simple microbial communities that allow easy characterization of the parameters determining microbial establishment and diversification. Soil samples were collected close to three different glacial lakes (Lake Fryxell, Lake Hoare and Lake Joyce) located along a longitudinal gradient from the lower to the upper Taylor Valley. Fungal diversity and functionality of sampled soils were studied through ITS1 metabarcoding sequencing. The correlation between the parameters describing fungal diversity (i.e. total richness, relative richness of dominant taxonomic and functional groups, and community composition) and the edaphic physicochemical parameters (i.e. pH, moisture, C, N, P, Na + , K + , Mg 2+ and Ca 2+ , cation exchange capacity, and soil granulometry) was assessed. The fungal communities showed low richness (48 ± 32 OTUs per sample). Their composition was highly diversified even within different sites close to the same lake. The main parameters affecting the diversity and composition of fungal communities were soil texture, in turn influencing the retention of water and nutrients, and physicochemical properties. This is of particular concern for the survival of these communities, given the expected environmental changes due to global warming.

Description of two new species of the africana-group of the Genus Gryllotalpa, with a redescription of Gryllotalpa africana Beauvois (Orthoptera: Gryllotalpidae)

Three species of the africana-group of the Genus Gryllotalpa (Orthoptera: Gryllotalpidae) were recorded from Cameroon during an investigation from March 2016 to March 2018: Gryllotalpa africana Beauvois from Buea and Tombel, and two new species, Gryllotalpa tombelensis Simeu-Noutchom and Kekeunou sp. nov. from Tombel and Gryllotalpa babetensis Simeu-Noutchom and Kekeunou sp. nov. from Babété. Gryllotalpa tombelensis is characterised by short wing morphology, vestigial hind wings, small phallic complex, short internal processes, and dorsoventrally flattened body. Gryllotalpa babetensis is distinct from other species of the africana-group by the mesoscutum being more exposed between the pronotum and the base of the fore wings, having a very large phallic complex, with very long internal processes of ectophallus (3 mm long). Both new species were collected in crop fields, but which differ in their habitat characteristics, such as soil moisture, pH and granulometry. A key and comments on the africana-group species of the genus Gryllotalpa and their habitat characteristics are also provided. The finding of the present study aims to help species identification and will help future taxonomists concerned with biodiversity of this group from Cameroon.

Impact of Biochar on Water Permeability in Soil

Water is the most important substance which occurs in nature. As a soil solution it is a basis of life for plants, both as an indispensable element of plant tissues as well as a carrier of mineral salts collected by plants through root hair. Ability to collect water by plants depends on the power of its binding with soil and thus on the quality of soil and amount of water. The objective of the article is to determine the water permeability in the superficial layer of soil in relation to the applied biochar dose. The research was provided in 2018 and 2019 year at agricultural field located in Krakow, Poland. The soil used for test was typical brown clay soil. The changes of soil granulometry were made with sunflower husk biochar. The biochar permeability was 3.2·10−5 m·s−1. The lowest value of water permeability 3.3·10−7 m·s−1 was observed for soil where 60 Mg·ha−1 of biochar was applied. Water permeability is strictly connected with general porosity and is often assumed as such in many papers. It was reported that the water permeability for control soil where no addition of biochar was used indicates up to two times lower permeability in comparison to the soil where biochar was added which indicates that biochar influences the amount of water available for plants which the investigated soils were able to store.

Consequences of removal of exotic species (eucalyptus) on carbon and nitrogen cycles in the soil-plant system in a secondary tropical Atlantic forest in Brazil with a dual-isotope approach.

The impact of exotic species on heterogeneous native tropical forest requires the understanding on which temporal and spatial scales these processes take place. Functional tracers such as carbon (δ13C) and nitrogen (δ15N) isotopic composition in the soil-plant system might help track the alterations induced by the exotic species. Thus, we assess the effects from the removal of the exotic species eucalyptus (Corymbia cytriodora) in an Atlantic forest Reserve, and eucalyptus removal on the alteration of the nutrient dynamics (carbon and nitrogen). The hypotheses were: (1) the eucalyptus permanence time altered δ13C and δ15N in leaves, soils and litter fractions (leaves, wood, flowers + fruits, and rest); and (2) eucalyptus removal furthered decomposition process of the soil organic matter. Hence, we determined the soil granulometry, the δ13C and δ15N in leaves, in the superficial soil layer, and litter in three sites: a secondary forest in the Atlantic forest, and other two sites where eucalyptus had been removed in different times: 12 and 3 months ago (M12 and M3, respectively). Litter samples presented intermediate δ13C and δ15N values in comparison with leaves and soil. In the M3, the greater δ13C values in both litter rest fraction and soil indicate the presence, cycling and soil incorporation of C, coming from the C4 photosynthesis of grassy species (Poaceae). In the secondary forest, the soil δ15N values were twice higher, compared with the eucalyptus removal sites, revealing the negative influence from these exotic species upon the ecosystem N dynamics. In the M12, the leaves presented higher δ13C mean value and lower δ15N values, compared with those from the other sites. The difference of δ13C values in the litter fractions regarding the soil led to a greater fractioning of 13C in all sites, except the flower + fruit fractions in the secondary forest, and the rest fraction in the M3 site. We conclude that the permanence of this exotic species and the eucalyptus removal have altered the C and N isotopic and elemental compositions in the soil-plant system. Our results suggest there was organic matter decomposition in all litter fractions and in all sites. However, a greater organic matter decomposition process was observed in the M3 soil, possibly because of a more intense recent input of vegetal material, as well as the presence of grassy, easily-decomposing herbaceous species, only in this site. Therefore, the dual-isotope approach generated a more integrated picture of the impact on the ecosystem after removing eucalyptus in this secondary Atlantic forest, and could be regarded as an option for future eucalyptus removal studies.

Treatment and reinforcement of the loose sands of the city of Kenitra

The Kenitra city belongs to the Rharb-Mamora domain, which is affected by a continuous subsidence from the Middle Vindobonien to the present day. The sedimentary cycle of the tertiary era ends at the Pliocene, characterized by regressive character deposits identified in outcrop at the margins of the basin: They are conglomerates in the North, yellow sands in the East, sands and sandstone in the South-East. These sandy deposits vary from more or less clayey sand to greying sand, with the appearance of a very loose sand layer, at varying depths. It is with this directive that the objective of this article is to define the risks, which may affect the works built on this soil, and also determine the actions to be taken to control these risks. As a first step, an experimental approach was carried out, including in situ and laboratory tests in order to identify these formations and define their mechanical behavior. Then, the results of geotechnical survey were analyzed and exploited in calculations of bearing capacity, settlement, liquefaction,… eventually resulting in the necessity of treatment and reinforcement of this soil. These approaches have shown that there are several soil reinforcement techniques, the choice of which depends on the granulometry of soil and the cost of project.

Comparing Field Sampling and Soil Survey Database for Spatial Heterogeneity in Surface Soil Granulometry: Implications for Ecosystem Services Assessment

Lithospheric-derived resources such as soil texture and coarse fragments are key soil physical properties that contribute to ecosystem services (ES), which can be valued based on “soil” or “mineral” stocks. Soil survey data provides an inexpensive alternative to detailed field measurements which are often labor-intensive, time-consuming, and costly to obtain. However, both field and soil survey data contain heterogeneous information with a certain level of variability and uncertainty in data. This study compares the potential of using field measurements and information from the Soil Survey Geographic database (SSURGO) for coarse fragments (CF), sand (S), silt (Si), clay (C) and texture class (TC) in the surface soil (Ap horizon) for the 147-hectare Cornell University Willsboro Research Farm, NY. Maps were created based on following methods: a) utilizing data from the SSURGO database for individual soil map unit (SMU) at the field site and using representative or reported values across individual SMU; b) averaging the field data within a specific SMU boundary and using the averaged value across the SMU; and c) interpolating field data within the farm boundaries based on the individual soil cores. This study demonstrates the important distinction between mapping using the “crisp” boundary soil SSURGO databases compared to the actual spatial heterogeneity of field interpolated data. Maps of CF, S, Si, C, and TC values derived from interpolated field core samples were dissimilar to maps derived by using averaged core results or SSURGO values over the SMUs. Dissimilarities in the maps of CF, S, Si, C, and TC can be attributed to several factors (e.g., official soil series data being collected from “type locations” outside of the study areas). Correlation plot of clay estimates for each SMU showed statistically significant correlations between SSURGO and field-averaged (r = 0.823, p = 0.003) and field-interpolated clay (r = 0.584, p = 0.028) estimates, but no correlation was found for CF, S, and Si.

How soil granulometry, temperature, and water predict genetic differentiation in Namibian spiders (Ariadna: Segestriidae) and explain their behavior.

The Namib Desert is a biodiversity hotspot for many invertebrates, including spiders. Tube‐dwelling spiders belonging to the Ariadna genus are widespread in gravel plains. These sit‐and‐wait predators share a particular behavior, as they spend their life in tunnels in the soil, surrounding the entrance of their burrow with stone rings. We investigated five spider populations taking into account environmental parameters, functional traits, and molecular data. We have chosen the temperature at the soil surface and at the bottom of the burrow, the air humidity, and the soil granulometry to define the environment. The chosen functional traits were the diameter and depth of the burrows, the ratio between weight and length, the thermal properties of their silks, and the number of ring elements. The molecular branch lengths and the evolutionary distance emerging from cytochrome oxidase I gene sequences summarized the molecular analysis. Our study highlights a strong coherence between the resulting evolutionary lineages and the respective geographical distribution. Multivariate analyses of both environmental and molecular data provide the same phylogenetic interpretation. Low intrapopulation sequence divergence and the high values between population sequence divergence (between 4.9% and 26.1%) might even suggest novel taxa which deserve further investigation. We conclude that both the Kimura distance and the branch lengths are strengthening the environmental clustering of these peculiar sites in Namibia.

Effects of some properties of cedar forest soils on secondary roots of Cedrus atlantica Manetti

The effect of textural and physicochemical characteristics of five cedar forest soils on 4- and 8-month-old seedlings of Cedrus atlantica Manetti was studied in a controlled growth chamber. During their growth, cedar seedlings show a change in the root architecture by the levels of C<sub>org</sub>, N, P, and by the soil granulometry. The Tioumlilin soil conditions stimulate mainly the cumulative length and the number of secondary roots. However, the cedar forest soil of Tazekka predominates over most soils in its effect on growth by the balance of chemical elements and the high percentage of coarse particles. The analysis of the densities of secondary and tertiary roots and the cumulative length of secondary roots show four different root architectural development strategies of C. atlantica seedlings which may justify the low level of mycorrhization on young seedlings in the natural cedar forest soil. The variations of the root architectural parameters of C. atlantica seedlings are discussed in relation to the characteristics of cedar forest soils.

Seasonal changes in dry matter yield from Karst pastures as influenced by morphoclimatic features.

Pastures are strongly affected by local environmental variables in terms of their species richness, plant composition and herbage production. A multi-site monitoring study was conducted over three years to investigate the influence of morphoclimatic factors on the seasonal variations in dry matter (DM) yield from Karst pastures. Seven sites located on the Italian and Slovenian Karst regions were investigated that differed in terms of their geological and geomorphological features, as well as their soil types. At each site, the daily DM yield (kg ha-1 d-1) was determined using Corral-Fenlon method which permits to simulate herbage utilization from grazing herds. The morphoclimatic features were also analysed, with the aim to evaluate the link between seasonal DM yield and geomorphological and environmental factors. Generalized non-linear mixed models were built to study the observed seasonal variations in DM yield, using day of the year (DOY), growing degree days (GDD), and cumulative rainfall. Furthermore, environmental descriptors were included in the model in order to evaluate their effects on DM yield. The seasonal variations in yield showed two growing periods (spring and late summer), which were described by Gaussian curves. For the spring growing period, the model improved when the interaction between soil granulometry and growing degree days corresponding to the curve peak was taken into account. This confirms the influence of soil type and air temperature on pasture yield. For the late summer growing period, the interaction between the sand classes and the number of rainy days from the beginning of the period to the peak of the curve improved the model. The curve parameters of our models are correlated with environmental descriptors depending on the lithology and particle size of soils. The results are essential for the optimization of pasture management and avoiding degradation due to over- or under-grazing.

Interference competition as a key determinant for spatial distribution of mangrove crabs

BackgroundThe spatial distribution of mangrove crabs has been commonly associated with tree zonation and abiotic factors such as ground temperature and soil granulometry. Conversely, no studies were designed to investigate the role of competition for resources and predation in shaping crab distribution in mangroves, despite these biotic factors are recognised as key determinants for spatial patterns observed in the communities colonising rocky and sandy intertidal habitats.We studied floral and faunal assemblages in two zones of a Sri Lankan mangrove, a man-made upper intertidal level and a natural eulittoral, mid-shore one. Leaf choice experiments were designed to study both feeding rate and intra and inter-specific interactions for food of sesarmid crabs in the two habitats in order to better understand crab spatial distribution.ResultsThe two intertidal belts differed in terms of floral composition and crab species abundance. The eulittoral zone was strongly dominated by Neosarmatium smithi, while within the elevated littoral fringe four sesarmids (N. smithi, N. asiaticum, N. malabaricum and Muradium tetragonum) were more evenly distributed. At both levels, all sesarmids showed to collect significantly more Bruguiera spp. and Rhizophora apiculata leaves than Excoecaria agallocha ones. There was no temporal segregation in feeding activity among the four species, resulting in a high interference competition for leaves. Regardless of the habitat, N. smithi was always successful in winning inter-specific fights.ConclusionsOur results showed that the elevated littoral fringe was more crowded with crabs, but was less favourable in terms of food availability and environmental conditions. The dominance of N. smithi in gathering mangrove leaves suggests that this species may segregate the other sesarmids into less favourable habitats. The present data strongly suggest for the first time that interference competition for food can contribute to shape mangrove crab spatial distribution.

Soil Physical Quality Indicators and Refinement of the Evaluation Method through the Srelative

This study aimed to verify the efficiency of indicators of measure of physical attributes’ alterations and to refine the Srelative determination method in order to increase its sensitivity to soil physical alterations. Soils under Ficus carica L. cultivation (with 0, 20, 40 and 60% of liquid bovine biofertilizer in the irrigation depth) and under forest were used. Parameters evaluated included soil granulometry, soil bulk and particle density, soil water retention curve (SWRC), porosity and the indices S and Srelative. The experimental design was completely randomized with four replicates. For Srelative refinement, with the SWRC containing only textural porosity, the soil was dispersed in water and with the addition of 1 N sodium hydroxide (with and without removal of sodium through washing). An ANOVA was performed for 0, 20, 40 and 60% of biofertilizer in 0-10, 10-20 and 20-30 layers; Dunnett test was used to compare the mean values of S-index and Srelative-index. With respect to four methods to obtain the Srelative-index the means were compared by Tukey test. Tests of line parallelism and intercept were performed for the regressions between each of the soil physical variables and Srelative-index obtained. It was found that S and Srelative indices were sensitive to soil physical alterations caused by the application of the biofertilizer; Srelative-index was sensitive to variation in soil bulk density and total porosity and the Srelative-index obtained from the method of soil dispersion in water is more sensitive to soil physical alterations in comparison to Srelative-index obtained through ADFE.

정동진 의사글레이층의 입도와 화학 조성에 대한 연구

정동진 의사글레이층의 입도와 화학 조성에 대한 연구

Thermal properties of soil in the Murrumbidgee River Catchment (Australia)

This paper presents analyses of topsoil thermal conductivity, heat capacity, thermal diffusivity, water content, and bulk density obtained during the Australian Airborne Cal/Val Experiment for SMOS. The aim of the study presented here is to identify the structure and variability of the spatial distribution of soil properties and their mutual dependencies. Knowledge of the spatial distribution of soil bulk density and water content is essential to develop precise agronomic practices to manage the thermal properties of the soil and the quality and efficiency of cultivated plants. Thermal properties of soils were obtained from in situ measurements and modelled using the Usowicz statistical-physical model which is based on simple physical soil properties. Two soil water content measurement methods (gravimetric and dielectric) and two soil granulometry classification systems (USDA and Australian) were used to find the most effective approach. It is shown that: (i) quartz and water content and the bulk density of soil are the main factors affecting the thermal properties of the soil; (ii) the spatial distribution of conductivity and heat capacity is governed by the soil water content distribution, while the thermal diffusivity near its maximum is mainly driven by the spatial distribution of the bulk density; and (iii) soil thermal properties were estimated more accurately from the Australian soil granulometry than the USDA classification. The results not only improved the scarce information about thermal properties of Australian soils, but allow to estimate the soil thermal properties across large scales from the physical properties of the soil (based on existing databases) and the current soil water content (from satellite and/or in situ measurements).

Application of chemical oxidation to remediate HCH-contaminated soil under batch and flow through conditions.

This is the first study describing the chemical oxidation of hexachlorocyclohexanes (HCHs) in contaminated soil under water saturated and unsaturated flow through conditions. Soil contaminated with β-HCH (45mgkg-1) and γ-HCH (lindane, 25mgkg-1) was sampled from former lindane waste storage site. Efficiency of following treatments was tested at circumneutral pH: H2O2 alone, H2O2/FeII, Na2S2O8 alone, Na2S2O8/FeII, and KMnO4. Experimental conditions (oxidant dose, liquid/solid ratio, and soil granulometry) were first optimized in batch experiments. Obtained results revealed that increasing dose of H2O2 improved the oxidation efficiency while in Na2S2O8 system, maximum HCHs were removed at 300mM. However, oxidation efficiency was slightly improved by FeII-activation. Increasing the solid/liquid ratio decreased HCH removal in soil samples crushed to 500μm while an opposite trend was observed for 2-mm samples. Dynamic column experiments showed that oxidation efficiency followed the order KMnO4>Na2S2O8/FeII>Na2S2O8 whatever the flow condition, whereas the removal extent declined at higher flow rate (e.g., ~50% by KMnO4 at 0.5mL/min as compared to ~30% at 2mL/min). Both HCH removal and oxidant decomposition extents were found higher in saturated columns than the unsaturated ones. While no significant change in relative abundance of soil mineral constituents was observed before and after chemical oxidation, more than 60% of extractable organic matter was lost after chemical oxidation, thereby underscoring the non-selective behavior of chemical oxidation in soil. Due to the complexity of soil system, chemical oxidation has rarely been reported under flow through conditions, and therefore our findings will have promising implications in developing remediation techniques under dynamic conditions closer to field applications.

A study on the wind erosion potential of agricultural lands after crop harvesting (Case study: Damghan Region)

Aeolian process and subsequently soil erosion are key factors in dryland environments. Such phenomena are related not only to geoecological factors (lithology, topography, and climatology) but also to land-use and plant cover changes. Formation of new sand dunes in Damghan explains the development of human activities over the past. The aim of this study is to explain the land use changes and their contributions and impacts on Aeolian sediments in Damghan Region. The study was carried out using topographic and geologic maps, satellite imagery, aerial photographs, meteorological data, field observation and samplings. According to meteorological data, period of strong winds (May to Jun) were identified. This period is wind activity period. So, based on this period, unprotected soil surface by crop residues with the interpretation of satellite images was determined. The field samples were carried out from May to June 2008 when the wind was active. The study methods include sieving soil granulometry, and analyzing the particle size. Granulometric analyses were performed using conventional dry sieve method. The results of statistical analysis of grain size distribution showed that the mean and median of particle size were composed of coarse and very coarse sand particles. The study indicated that 90% of the agricultural lands contained more than 23% soil aggregates, where in areas with sensitive particles to erosion the Figure was 35%. It can be argued that agricultural land in study area are resistant to wind erosion.

Physical soil attributes of Conilon coffee (Coffea canephora) under organic and conventional management systems

Coffea sp. is cultivated in large areas, using both conventional and organic management. However, information about the sustainability of these two management systems is still deficient. The objective of the present study was to evaluate the physical properties of soil cultivated with Conilon coffee (C. canephora) under organic and conventional management. Two areas cultivated with Conilon coffee (under organic and conventional management) and a fragment of Atlantic forest, used as a reference, were selected for the experiment. Soil granulometry, hydraulic conductivity, water retention curve, resistance to penetration, porosity, optimal hydric interval, and other physical characteristics were measured at depths of 0 to 10 and 10 to 20 cm. The data was submitted to multivariate and descriptive statistical analyses. Higher similarity was observed between the soil cultivated with Conilon coffee under organic management and the Atlantic forest soil. Soil resistance to penetration at 10, 30, 100, 500 and 1500 kPa, macro porosity, density and total porosity were the main physical properties that differentiated both management systems studied. The non-use of agricultural machinery and the addition of organic matter may be the main reasons for higher soil sustainability observed under organic management when compared with the conventional system.

Capacity and intensity soil aeration properties affected by granulometry, moisture, and structure in no-tillage soils

Soil surface is the locus of complex apportioning of mass and energy reaching the Earth. Pore system functioning of the surface soil, particularly airflow within the soil matrix, is affected by soil deformation. Our objective was to evaluate the effect of soil structure, moisture, and granulometry on soil aeration properties of three Oxisols and one Ultisol managed under no-tillage. Undisturbed samples (572), collected from loose (0.00–0.075m) and compact (0.075–0.15m) soil layers, were capillary saturated for 24h and equilibrated to nine water tensions, from 1 to 500kPa, to determine capacity (bulk density, volumetric moisture, air-filled porosity, and degree-of-compactness) and intensity (air conductivity and permeability, blocked porosity, and pore continuity) soil physical properties related to aeration; whereas disturbed soil samples were used for soil granulometry analysis. Soil granulometry, moisture, and structure (soil compaction) affect aeration capacity and intensity properties. Regardless of soil wetness, soil compaction reduces air-filled porosity, pore continuity, and air permeability. As soil moisture decreases, air permeability increases because of greater amount and continuity of soil pores available for air flow, and this increase in permeability is greatest in sandy-textured soil compared with clay-textured soils. Intensity properties are better descriptors of the time-variable aeration status of long-term no-tilled soils.

Increase in soil aggregate stability along a Mediterranean successional gradient in severely eroded gully bed ecosystems: combined effects of soil, root traits and plant community characteristics

Our objectives were to evaluate changes in soil aggregate stability along a successional gradient, located in severely eroded Mediterranean gully bed ecosystems and to identify predictors of soil aggregate stability variations among several soil, root traits and plant community characteristics. We selected 75 plots in gully beds, representing five successional stages that differ in plant community composition, dominated by herbs, shrubs or trees according to successional stage. In each plot, we measured soil aggregate stability, basic soil characteristics, root traits and plant diversity indices. Soil aggregate stability increased along the successional gradient, being thrice higher in tree-dominated communities as compared to grass-dominated communities. This increase was mainly driven by soil organic carbon (SOC) accumulation. In early successional stages showing low SOC (below 24 g.kg−1 or 12 g.kg−1 in some cases), fine sand content and the percentage of fine roots acted as co-drivers enhancing soil aggregate stability while silt content decreased it. Plant succession in severely eroded Mediterranean gully bed ecosystems is accompanied by a strong stabilization of soil aggregates, mainly driven by SOC accumulation and for early successional stages, by soil granulometry and root traits as co-drivers. Stimulating succession thus appears as a promising restoration strategy for severely eroded ecosystems.