Mediterranean Soils Research Articles

Soil-Easily Extractable Glomalin: An Innovative Approach to Deciphering Its Molecular Composition under the Influence of Seasonality, Vegetation Cover, and Wildfire.

Easily extractable glomalin (EEG) is a fraction of soil organic matter thought to contain mainly glomalin-related soil glycoproteins produced by mycorrhizal fungi. The EEG has an impact on various soil ecological functions, primarily related to soil aggregation formation and stability as well as water repellence. Here, analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used for studying the molecular composition of soil EEG, and a detailed description of the chemical composition is reported. Samples extracted from Mediterranean soils under different vegetation covers (Pinus halepensis and shrubland species, Rosmarinus officinalis, and Brachypodium spp, predominantly), impacted or not by forest fires and collected at different times, were studied. A total of 139 compounds were identified and grouped based on their probable biogenic origin. The EEG chemical composition is dominated by lipids, aromatic compounds, steranes, and hydroaromatics with a remarkable abundance of compounds from plant origin. Significant EEG structural changes can indicate environmental disturbances such as those after a wildfire. The EEG soil organic fraction is found to be a stable and heat-resistant material in nature if soil temperatures remain below 200-250 °C. This study advances the understanding of EEG by providing a detailed molecular characterization and highlighting its role as a stable, heat-resistant component of soil organic matter in Mediterranean ecosystems. The main findings indicate that while EEG is structurally resilient and mostly originates from plant material, its composition is more similar to that of humic acids than to that of glycoproteins.

Performance and land characteristics of brackishwater pond to support sustainability of Pacific white shrimp (Litopenaeus vannamei) culture intensive technology.

Intensive technology Pacific white shrimp (Litopenaeus vannamei) culture has been applied in Bulukumba Regency, South Sulawesi Province, but information on the performance of Pacific white shrimp culture and the land characteristics or environment of the pond has not yet been obtained. The research purposes are to find out the performance and the land characteristics or environment of Pacific white shrimp culture intensive technology to serve as a basis for determining the culture development. Five transects perpendicular to the shoreline and three transects parallel to the coastline, or 15 water sample stations, were identified in the field. Other data was obtained from the extraction of Sentinel-2 and SPOT (Satellite pour l'Observation de la Terre) satellite imagery 7. The size of intensive technology Pacific white shrimp culture ponds in Bulukumba Regency ranges from 1600 to 5000 m2 which is stocked with fry with a stocking density of 100-300 ind./m2 which can produce 12.0-50.0 tons/ha/cycle after rearing for 100-142daysof culture with a food conversion ratio of 1.2:1-2.0:1. The land characteristics of intensive technology Pacific white shrimp culture ponds in Bulukumba Regency are characterized by elevation from 10.0 to 20.0m above sea level, wavy topography, tidal range between 1.35 and 1.70m, dominated by Latosol or Cambisol and Alfisol or Mediterranean soil great groups, the quality of the source water can generally support Pacific white shrimp culture, and the annual rainfall is from 1341 to 1763mm and it is not built on former mangrove land. It is recommended that existing Pacific white shrimp culture ponds increase the capacity and capability of their wastewater treatment plant ponds and implement better water management and feed management so that the quality of wastewater from intensive technology Pacific white shrimp culture ponds can also be better so that productivity can be increased and sustainable.

Impact of Drying–Wetting Cycles on Nitrification Inhibitors (DMPP and DMPSA) in a Greenhouse Experiment with Two Contrasting Mediterranean Soils

Studies of the impact of nitrification inhibitors (NIs), specifically DMPP and DMPSA, on N2O emissions during “hot moments” have produced conflicting results regarding their effectiveness after rewetting. This study aimed to clarify the effectiveness of NIs in reducing N2O emissions by assessing residual DMP concentration and its influence on ammonia-oxidizing bacteria (AOB) in two pot experiments using calcareous (Soil C, Calcic Haploxerept) and acidic soils (Soil A, Dystric Xerochrepts). Fertilizer treatments included urea (U), DMPP, and DMPSA. The experiments were divided into Phase I (water application to dry period, 44 days) and Phase II (rewetting from days 101 to 121). In both phases for Soil C, total N2O emissions were reduced by 88% and 90% for DMPP and DMPSA, respectively, compared with U alone. While in Phase I, the efficacy of NIs was linked to the regulation of AOB populations, in Phase II this group was not affected by NIs, suggesting that nitrification may not be the predominant process after rewetting. In Soil A, higher concentrations of DMP from DMPP were maintained compared to Soil C at the end of each phase. Despite this, NIs had no significant effect due to low nitrification rates and limited amoA gene abundance, indicating unfavorable conditions for nitrifiers. The study highlights the need to optimize NIs to reduce N2O emissions and improve nitrogen efficiency, while understanding their interactions with the soil. This knowledge is necessary in order to design fertilization strategies that improve the sustainability of agriculture under climate change.

Adsorption and mineralization of metalaxyl-m and chlorpyrifos in irrigated Mediterranean soil under the effects of salinity.

To evaluate the effects of salinity on the fate of pesticides in a Mediterranean irrigated system, experiments were carried out under laboratory conditions to determine the adsorption, desorption, and mineralization of chlorpyrifos (CPF) and metalaxyl-M (MET) in a soil sample from an irrigated field in northern Tunisia. Adsorption/desorption isotherms and mineralization kinetics data were obtained over a realistic range of salinities via batch equilibrium and incubation techniques. On the basis of the experimental results, MET has a lower sorption capacity than CPF does, and the adsorption data for both compounds were better fitted by the Freundlich equation, with Kf values of 0.477, 0.486, 0.426, 0.444 and 0.474 L kg-1 for MET and 38.994, 39.084, 40.644, 44.055 and 45.185 L kg-1 for CPF at salinities of 0, 1, 2, 5 and 10 g L-1, respectively. According to the mineralization experiments, increasing salinity increased the half-lives of both pesticides. For MET, the DT50 values in unsterilized soil were 206.68, 220.74, 222.16, and 238.73 days, and those in sterilized soil were 2772.58, 4077.33, 6301.33, and 8664.33 days at salinities of 0, 1, 2, 5, and 10 g L⁻1, respectively. For CPF, the DT50 values were 115.52, 138.62, 157.53, and 177.73 days in unsterilized soil and 346.57, 533.19, 693.14, and 990.21 days in sterilized soil. In terms of leaching behavior, the calculated groundwater ubiquity score (GUS) values for the MET and CPF indicate that the MET is classified as a leacher and that the CPF is classified as a nonleacher.

Influence of Arsenate Competition on Tungstate Sorption by Soil

The green and digital transitions toward sustainable development will drive an increased demand for critical raw materials, among which tungsten plays a crucial role in emerging sustainable technologies. Understanding the sorption processes of tungsten in soils is essential for assessing its bioavailability and potential toxicity to living organisms. In many soils, tungsten may co-exist with other contaminants, such as arsenic. Investigating the competitive sorption between these two anions helps clarify how they interact within the soil matrix. Batch experiments were conducted on three Mediterranean soils to evaluate the sorption behavior of tungstate and arsenate, both individually and in combination, using a “Langmuir-type” model. Both anions exhibited the highest sorption in acidic soils and the lowest in alkaline soils. While the shapes of the isotherms were similar in both single and binary systems, the maximum sorption values decreased when a co-occurring anion was present. These reductions can be attributed to competition for soil sorption sites, which have a high affinity for both anions. In all tested soils, the percentage decrease in arsenate sorption in the presence of tungstate was greater than the decrease observed for tungstate in the presence of arsenate. Gaining a deeper understanding of tungsten’s sorption mechanisms is critical, not only for advancing environmental research but also for informing regulations that currently give limited attention to the presence of tungsten in soils.

Rehabilitation of a degraded acid Mediterranean soil after 11 years of by‐product calcium amendments and pasture improvement

AbstractThe clearing of natural vegetation and tillage for agricultural purposes makes acid soils highly vulnerable to degradation, resulting in significant losses of soil fertility and crop productivity. This work focused on nature‐based agricultural solutions to rehabilitate degraded acid soils in low‐resource systems. We studied after 6 and 11 years how the introduction of a legume‐rich pasture replacing a natural pasture or a tilled forage crop, with and without Ca‐amendment, contributed to recover the soil health, the fertility and the productivity of degraded Ultisols in Western Spain. Industrial by‐products, mainly sugar foam, were used as Ca‐amendment to promote circular economy. The Ca‐amendment factor influenced soil chemistry to 30 cm depth, while the type of soil use affected soil organic matter (SOM) to 15 cm; and both factors had positive effects on biomass productivity. Except for pH and Ca, no interaction between factors was found. Ca‐amendment increased nutrient availability and soil pH, and Al ion precipitated at 0–15 cm depth. As a result, biomass production increased by 35% relative to no Ca‐amendment. Forage cop produced 66% more biomass than pastures, but this increase did not translate into an increase in SOM. In fact, the legume‐rich pasture was the best option to recover soil organic C and N levels, earlier and deeper. Over the 11 years, the use of pastures and Ca‐amendment enhanced biomass production stability. Relative to natural, the improved pasture did not increase plant biomass but provided higher biomass stability and quality in terms of legume abundance, which was promoted when sugar foam was applied. Pastures also favoured key biological variable as earthworm's population, increasing it by four times with respect to forage crops. Compared to the non‐amended and unfertilized natural pasture out of the experiment, the use of improved pasture, followed by natural pasture, combined with sugar foam and fertilization enhanced soil health, soil fertility and biomass production stability. Thus, this solution has proven effective for restoring degraded acid soils, promoting diversity and mitigating climate change, while offering a more economically beneficial alternative.

Fire enhances changes in phosphorus (P) dynamics determining potential post-fire soil recovery in Mediterranean woodlands

Soil phosphorus (P), which is essential for ecosystem functioning, undergoes notable changes after fire. However, the extent to which fire characteristics affect P dynamics remains largely unknown. This study investigated the impact of type of fire (prescribed burning and natural wildfires) of different levels of severity on P dynamics in Mediterranean soils. Soil P concentrations in the organic layers were strongly affected by fire severity but not fire type. Low severity fire did not have any observable effect, while moderate fire increased soil P levels by 62% and high severity decreased soil P concentration by 19%. After one year, the soil P concentration remained unchanged in the low severity fires, while rather complex recovery was observed after moderate and high severity fires. In the mineral layers, P concentration was reduced (by 25%) immediately after the fires and maintained for one year (at 42%). 31P-NMR spectroscopy revealed almost complete post-fire mineralization of organic P forms (mono- and diesters), large increases in inorganic orthophosphate and a decrease in the organic:inorganic P ratio (Po:Pi). After one year, di-esters and orthophosphate recovered to pre-fire levels at all sites, except those where parent material composition (high pH and Fe concentration) had an enduring effect on orthophosphate retention, and thus, on the total soil P. We showed that fire severity and soil pH (and hence, soil mineralogy) played an essential role in soil P dynamics. These findings are important for reliable assessment of the effects of fire on soil P conservation and for improving the understanding the impact of prescribed burning.

Use of Cannabis sativa L. for Improving Cadmium-Contaminated Mediterranean Soils—Effect of Mycorrhizal Colonization on Phytoremediation Capacity

Although the phytoremediation strategy has been studied worldwide, little research data are available regarding the influence of mycorrhizae on the phytoremediation capacity of various plants grown in Cd-contaminated soils in Mediterranean environments. Therefore, a pot experiment was carried out to study the possible effectiveness of hemp plant (Cannabis sativa L.) in the remediation of moderately and heavily Cd-contaminated soils and additionally to quantify the effect of Cd on Arbuscular Mycorrhizal Fungi (AMFs). For this purpose, an alkaline clay soil collected from the Farm of Institute of Plant Breeding and Genetic Resources (North Greece) was contaminated with two levels of Cd (3 and 30 mg Cd kg−1, corresponding to Levels A and B, respectively—first factor) at two incubation times (10 and 30 days—second factor) and six treatments (Control_30d, Control_10d, CdA_30d, CdB_30d, CdA_10d, CdB_10d) were created. Soil Cd concentrations, both pseudo-total and available to plants, were determined after extraction with Aqua Regia mixture and DTPA solution, respectively, before and after the cultivation of hemp plants and after the harvesting. Cd concentrations in the aboveground and underground plant parts were also estimated after digestion with Aqua Regia, while root colonization by AMFs was determined with a microscope. The highest plant’s Cd concentration, more than 50%, was observed in its underground part, at all Cd-contaminated treatments, indicating a strong capacity for cadmium to gather up in the roots. Among different Cd levels and incubation days, significant differences were recorded in the rates of root colonization by AMFs. Among different Cd levels and incubation days, 3 mg Cd Kg−1 soil promoted AMF root colonization, particularly at 10-day incubation, while 30 mg Cd Kg−1 soil diminished it. Colonization was lower with longer incubation times at both levels of Cd. Hemp appears to be a viable option for phytostabilization in Cd-contaminated soils, enabling further utilization of AMFs to assist the phytoremediation process.

Different seasons and vegetation cover more than fire control nutrient stoichiometry and biological activities in Mediterranean soils

Mediterranean soils are affected by degradation phenomena, exacerbated by anthropic disturbance. These ecosystems are affected by peculiar climatic conditions, characteristic vegetation and frequent fire that with the anthropic activities can compromise soil nutrient status. Studies concerning the nutrients stoichiometry in Mediterranean area are scarce, therefore the present research aim to fill the gap about the effect of seasonal variations, vegetation cover and fire occurrences on soil nutrient balance and microbial biomass and activity. The sampling was performed inside the Vesuvius National Park across 24 sites during two seasons (Fall and Spring), under trees and shrubs and in burned and unburned areas. Soils were characterized for carbon (C), nitrogen (N), phosphorous (P) and potassium (K) concentrations, for bacterial and fungal biomass (Eub and Fungi) and for microbial activities (respiration, hydrolase: HA, dehydrogenase: DHA, β-glucosidase: β-glu and urease: U). The results showed that, both in Fall and Spring, high C:N (18.7), C:P (130) and N:P (6.74) ratios were observed in soils under trees. Both in soils under trees and shrubs, low eubacterial biomass (trees: 90.2 ng g−1 w.w.; shrubs: 44.4 ng g−1 w.w.), respiration (trees: 0.24 mg CO2 g−1 d.w. min−1; shrubs: 0.14 mg CO2 g−1 d.w. min−1) and hydrolase (trees: 37.0 mmol FDA g−1 d.w. min−1; shrubs: 11.9 mmol FDA g−1 d.w. min−1) activities were observed in Spring. Fire effect was evident only in Fall where low values of eubacterial biomass (667 ng g−1 w.w.) and respiration activity (0.60 mg CO2 g−1 d.w. min−1) were observed in burnt soils. In conclusion, the seasonal variations and the vegetation cover appeared the main environmental factors that affect nutrient stoichiometry and microbial biomass and activity in Mediterranean soils. It is necessary to monitor Mediterranean soils during different seasons and encourage the growth of native vegetation to enhance nutrient cycling and maintain soil health.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Bismuth Film along with dsDNA-Modified Electrode Surfaces as Promising (bio)Sensors in the Analysis of Heavy Metals in Soils.

Heavy metals constitute pollutants that are particularly common in air, water, and soil. They are present in both urban and rural environments, on land, and in marine ecosystems, where they cause serious environmental problems since they do not degrade easily, remain almost unchanged for long periods, and bioaccumulate. The detection and especially the quantification of metals require a systematic process. Regular monitoring is necessary because of seasonal variations in metal levels. Consequently, there is a significant need for rapid and low-cost metal determination methods. In this study, we compare and analytically validate absorption spectrometry with a sensitive voltammetric method, which uses a bismuth film-plated electrode surface and applies stripping voltammetry. Atomic absorption spectroscopy (AAS) represents a well-established analytical technique, while the applicability of anodic stripping voltammetry (ASV) in complicated sample matrices such as soil samples is currently unknown. This sample-handling challenge is investigated in the present study. The results show that the AAS and ASV methods were satisfactorily correlated and showed that the metal concentration in soils was lower than the limit values but with an increasing trend. Therefore, continuous monitoring of metal levels in the urban complex of a city is necessary and a matter of great importance. The limits of detection of cadmium (Cd) were lower when using the stripping voltammetry (SWASV) graphite furnace technique compared with those obtained with AAS when using the graphite furnace. However, when using flame atomic absorption spectroscopy (flame-AAS), the measurements tended to overestimate the concentration of Cd compared with the values found using SWASV. This highlights the differences in sensitivity and accuracy between these analytical methods for detecting Cd. The SWASV method has the advantage of being cheaper and faster, enabling the simultaneous determination of heavy elements across the range of concentrations that these elements can occur in Mediterranean soils. Additionally, a dsDNA biosensor is suggested for the discrimination of Cu(I) along with Cu(II) based on the oxidation peak of guanine, and adenine residues can be applied in the redox speciation analysis of copper in soil, which represents an issue of great importance.

Adsorption of sulfamethoxazole and ethofumesate in biochar- and organoclay-amended soil: Changes with adsorbent aging in the laboratory and in the field

Biochars and organoclays have been proposed as efficient adsorbents to reduce the mobility of agrochemicals in soils. However, following their application to soils, these adsorbents undergo changes in their physicochemical properties over time due to their interaction with soil components. In this study, the adsorption capacity of a commercial biochar and a commercial organoclay for the antibiotic sulfamethoxazole (SFMX) and the pesticide ethofumesate (ETFM) was evaluated over aging periods of 3 months in the laboratory and 1 year in the field, subsequent to their application to a Mediterranean soil. The results showed that the adsorption of SFMX and ETFM in the soil amended with the adsorbents was greater than in the unamended soil, but for both chemicals, adsorption decreased with aging of the adsorbents in the soil. Characterization of the adsorbents before and after aging revealed physical blocking of adsorption sites by soil components. The loss of adsorption capacity of the adsorbents upon aging led to higher leaching of SFMX and ETFM in the soil containing field-aged adsorbents, although leaching remained lower than in unamended soil. Our findings reveal that, under the Mediterranean environment studied, the efficacy of the studied materials as adsorbents is maintained to a considerable extent for at least one year after their field application, which would have positive implications in their use for attenuating the dispersion of agricultural contaminants in the environment.

The Imperishable Rays of Byzantinism. On the Occasion of the 85th Anniversary of the Birth of the “Mediterranean Soil Scientist” Academician S. S. Averintsev

The Imperishable Rays of Byzantinism. On the Occasion of the 85th Anniversary of the Birth of the “Mediterranean Soil Scientist” Academician S. S. Averintsev

Potential valorization and transformation of plastic biomass waste into useful fertilizers in agricultural Mediterranean soils under extreme climate conditions

Plastics are widely used in agricultural practices, although recently they have been recognized as a new emerging risk in soils. Polyethylene (PE), is commonly used by farmers to cover agricultural practices; geotextile, is used mainly for ground and crop covering; and polyvinyl chloride (PVC) is considered the main material contained in irrigation hoses. The present study aimed to assess the effects of three plastics (polyethylene, geotextile, polyvinyl chloride) on the soils’ fertility. Several pot experiments were conducted in soil samples from the study area (Thessaly) contaminated with adequate amounts of each plastic type (PE, geotextile: 2% v/v and PVC: 5% v/v). Water was added in two quantities: one to maintain typical soil moisture levels according to the crops’ requirements and an elevated amount to form supersaturating soil conditions similar to those following a flood event. Furthermore, temperature effect was also investigated to assess its impact on plastics’ behavior and soil fertility. The levels of all nitrogen forms and the microbial activity were determined at 10, 30, and 60 days. Significant changes were observed in the concentrations of nitrate, nitrite, and ammonium ions under ambient soil moisture conditions especially when the microplastics were incubated for a longer period. PE addition resulted in greater changes, followed by geotextile, although PVC addition did not induce significant changes in the nitrification process during the experimental time. PE and geotextile microplastics appeared to enhance microbial colonization and total microbial activity. In addition, soil characteristics were notably altered when moisture stress conditions were reached (85%) and when soils were flooded for two months, leading to a severe decrease in the availability of all nitrogen forms. The results showed that alterations in soil nitrogen forms in the presence of plastics study are crucial for maintaining the health and improving the productivity of Mediterranean soils.

Biochar Addition to a Mediterranean Agroecosystem: Short-Term Divergent Priming Effects

The goal of this study was to evaluate biochar’s resistance to microbial decomposition and its impact on native soil organic matter (SOM) decomposition. Conducted in a vineyard with a sandy loam Mediterranean soil with neutral pH and low organic carbon content, the experiment involved the application of 6.5 g biochar kg−1 derived from pine (PB) and corn cob (ZB). The monitoring period spanned two years, with soil samples collected at short- and medium-term timepoints (2 and 26 months post-application) and incubated in the lab for an additional 250 days. Soil respiration, the CO2-C isotopic signature, and dissolved organic carbon (DOChw) were assessed to identify potential priming effects (PE) and evaluate their persistence over two years. In the short term, biochar-induced priming effects were feedstock and pyrolysis temperature dependent, exhibiting negative priming in high-temperature wood biochar and positive priming in low-temperature grass biochar. The mechanism behind short-term positive priming was attributed to the higher labile organic carbon (OC) content in ZB compared to PB. In the medium term, initial strong priming effects shifted to slightly negative priming effects in both biochars, indicating the depletion of labile carbon fractions and the emergence of physical protection processes that mitigated priming.

Tungsten Bioaccessibility and Environmental Availability in Tungsten-Spiked Agricultural Soils

Tungsten is an essential element for many cutting-edge industries. Its use is increasing, so much that it has become a “critical element”. With the increase in the use of tungsten, a possible increase in its presence in environmental matrices including soil is expected. In this research, we assessed the environmental availability and bioaccessibility of W in relation to soil properties. Four representative Mediterranean soils, collected in Italy, were spiked with tungsten and incubated for 12 months. In the spiked soils, the environmental availability of the element was determined by the Wenzel sequential extractions. The bioaccessibility was determined by the UBM (BARGE) method in both the gastric and intestinal phases. The findings indicated that the environmental availability is largely influenced by soil properties such as pH and organic matter, while a lower influence was discovered for bioaccessibility, particularly for the gastric phase. These differences could be ascribed to the characteristics of the extractants utilized in the various tests, in particular the pH values. These results could be a valuable reference to integrate with studies on really and not spiked contaminated soils, for the improvement of risk assessments and the development of strategies for remediating soils polluted with tungsten.

Phytoremediation & Valorization of Cu-contaminated Soils Through Cannabis sativa (L.) Cultivation: A Smart Way to Produce Cannabidiol (CBD) in Mediterranean Soils

PurposeThe potential of industrial hemp (Cannabis sativa L.) for phytoremediation of copper-contaminated Mediterranean soils was investigated. The accumulation of copper in hemp’s parts and the effect of contaminated soil on the production of cannabidiol (CBD) were, also, of primary concern.MethodsTwo soil types, a Clay Loam & a Sandy Clay Loam, were exposed to two levels of Cu contamination, with low & high Cu concentrations. The soils’ total and available Cu content, along with Cu in plant tissues, were determined. Height, fresh aboveground biomass and leaf chlorophyll content were further evaluated. Furthermore, the amount of cannabidiol (CBD) in the hemp flowers was determined.ResultsHemp appeared to be highly resistant, as can successfully grow in both soil types having low or high Cu levels. The maximum Cu content was detected in the highest part of the plant roots, with a progressive decline towards the upper parts of the plant (CuRoots > CuShoots > CuLeaf), in both soil types. It has been observed that more than 50% of the plant’s copper concentration is accumulated in the roots. Furthermore, the hemp plants cultivated in high Cu-contaminated soils produced greater amounts of cannabidiol (CBD).ConclusionΗemp proved to be a promising plant for phytostabilization in Cu-contaminated soils, as its above-ground biomass is almost free of metals and can be used further for fiber production. The presence of Cu in soils did not appear to disrupt the production of the important secondary metabolite CBD, but rather increased following increasing soil Cu content.Graphical

Improved soil carbon stock spatial prediction in a Mediterranean soil erosion site through robust machine learning techniques.

Soil serves as a reservoir for organic carbon stock, which indicates soil quality and fertility within the terrestrial ecosystem. Therefore, it is crucial to comprehend the spatial distribution of soil organic carbon stock (SOCS) and the factors influencing it to achieve sustainable practices and ensure soil health. Thus, the present study aimed to apply four machine learning (ML) models, namely, random forest (RF), k-nearest neighbors (kNN), support vector machine (SVM), and Cubist model tree (Cubist), to improve the prediction of SOCS in the Srou catchment located in the Upper Oum Er-Rbia watershed, Morocco. From an inventory of 120 sample points, 80% were used for training the model, with the remaining 20% set aside for model testing. Boruta's algorithm and the multicollinearity test identified only nine (9) factors as the controlling factors selected as input data for predicting SOCS. As a result, spatial distribution maps for SOCS were generated for all models, then compared, and further validated using statistical metrics. Among the models tested, the RF model exhibited the best performance (R2 = 0.76, RMSE = 0.52 Mg C/ha, NRMSE = 0.13, and MAE = 0.34 Mg C/ha), followed closely by the SVM model (R2 = 0.68, RMSE = 0.59 Mg C/ha, NRMSE = 0.15, and MAE = 0.34 Mg C/ha) and Cubist model (R2 = 0.64, RMSE = 0.63 Mg C/ha, NRMSE = 0.16, and MAE = 0.43 Mg C/ha), while the kNN model had the lowest performance (R2 = 0.31, RMSE = 0.94 Mg C/ha, NRMSE = 0.24, and MAE = 0.63 Mg C/ha). However, bulk density, pH, electrical conductivity, and calcium carbonate were the most important factors for spatially predicting SOCS in this semi-arid region. Hence, the methodology used in this study, which relies on ML algorithms, holds the potential for modeling and mapping SOCS and soil properties in comparable contexts elsewhere.

Soil legacy and organic amendment role in promoting the resistance of contaminated soils to drought

The application of organic amendments is a common practice in the restoration of contaminated and degraded soils. We designed an experiment in pot mesocosms to study the effect of organic amendment (comparing a short-term addition of biosolid compost with soils amended 17 years ago) and soil legacy (comparing soils exposed or not to extensive grazing over a remediation process) on the resistance of a degraded Mediterranean soil against a simulated drought event. Pots were sown with a forage mixture (Lolium rigidum and Medicago polymorpha), and soil resistance was evaluated by measuring soil chemical properties, biological activity (soil enzyme activities and respiration rate), soil microbial community composition and plant production. Our results showed a positive effect of the organic amendment and the exposure to extensive grazing on soil properties, increasing soil water retention and the stability of plant production under drought conditions. The long-term amendment addition avoided the negative consequences of drought on L. rigidum production (the species with the lowest tolerance to water stress), while M. polymorpha biomass in soils exposed to grazing was 12 times the biomass in the non-amended and non-exposed soil. However, soil biological activity (enzyme activities and respiration rate) as well as microbial diversity were not limited by the simulated drought conditions under any type of soil management legacy, demonstrating the great adaptation of the microbial communities to water stress conditions in semiarid Mediterranean soils. Soils exposed to organic matter inputs in the long-term, through amendment addition or exposure to grazing, showed high similarities in terms of bacterial and fungal composition.

Carbon and nutrient colimitations control the microbial response to fresh organic carbon inputs in soil at different depths

Despite the potential of subsoil carbon (C) to buffer or amplify climate change impacts, how fresh C and nutrients interact to control microorganismal effects on the C balance in deep soil horizons has yet to be determined. In this study, we aimed to estimate the impact of fresh C input at different soil depths on soil microbial activity. To conduct this study, Mediterranean soils from 3 layers (0–20, 20–50 and 50–100 cm of depth) were incubated over 28 days. Carbon and nutrient fluxes were measured after the addition of an amount of C equivalent to the postharvest root litter derived-C of a barley crop (4.3 atom% 13C), with and without nitrogen and phosphorus supply. We found that the microbial mineralization was C limited in the topsoil, while C and N colimited in the subsoil. These variations in stoichiometric constraints along the soil profile induced different microbial responses to C and/or nutrient addition. A stronger priming effect was observed in the topsoil than in the subsoil, and the sole C addition induced a negative C balance. Conversely, subsoil showed a positive C balance following fresh C addition, changing to critical soil C losses when nutrients were supplied with C. Our results show that fresh C input to subsoil (e.g., through deep-rooting crops) might foster soil C sequestration, but this positive effect can be reversed if such C inputs are combined with high nutrient availability (e.g., through fertilization), alleviating microbial limitation at depth.