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Global warming effects in our ecosystems could be offset by reducing carbon emissions and protecting and increasing carbon stocks. Accurate estimates of carbon stocks and fluxes of soil organic carbon (SOC) are thus needed to asses the impact of climate and land-use change on soil C uptake and soil C emissions to the atmosphere. Here, we present an assessment of SOC stocks in woodlands (forest, shrublands and grasslands) of peninsular Spain based on field measurements in more than 900 soil profiles. Estimations of soil C stocks for the 7 796 306 plots of the Spanish Forest Map (24.3 X 106 ha.) were carried out using a statistical model that included, as explanatory variables, vegetation cover, parent material, soil consistency, mean annual temperature, total annual precipitation and elevation, and the influence of spatial correlation. We present what we believe is the most reliable estimation of current SOC in woodlands of peninsular Spain thus far, based on the considered predictors, the high number of profiles and the validity and refinement of the data layers employed. Mean concentration of SOC was 8.8 kgm-2, which is slightly higher than that presented in previous studies. This value corresponds to a total stock of 2574TgSOC, which is four times the amount of carbon estimated to be stored in the biomass of Spanish forests. Climate and vegetation cover were the main variables influencing SOC, with important ecological implications for peninsular Spanish ecosystems in the face of global change. The fact that SOC was positively related to annual precipitation and negatively related to mean annual temperature suggests that future climate change may strongly reduce the potential of Spanish soils as carbon sinks. However, this may be mediated by changes in vegetation cover (e.g., by favouring the development of forests associated to higher SOC values) and threatened by perturbations such as fire. The estimations presented here should improve our capacity to respond to global change by carbon stocks conservation and management. [ABSTRACT FROM AUTHOR]

The article discusses the study which quantifies and explores the role of land use and soil as determinants of soils' ability to store carbon (C) along Mediterranean systems. The study investigated the soil organic C (SOC) contents from different soil and land use types in Andalusia, Spain. The study used soil information from different databases, digital maps, and digital elevation models. Results show that SOC stocks were calculated for each combination of land use and soil type.

Urban and peri-urban agriculture is one of the strategies that emerged on the path towards agri-food sustainability in cities. This paper aims at improving the knowledge of the soil properties in a peri-urban area and their agricultural potential to support ecosystems with biodiversity worth conserving. The study area was located in the mid-plain of the Segura River (SE Spain). Arable soil layer samples were collected at 68 points to assess the distribution of organic carbon and to study other indicators of soil quality. A Wilcoxon and Kruskal–Wallis test was conducted to compare between the types of soils present in the area (calcaric Fluvisols and calcaric Regosols) and soil uses (industrial, cultivated and abandoned). Statistical analysis indicates that there are significant differences (at the 0.05 significance level) between Fluvisols and Regosols (p value = 3.65 × 10−5). Regarding use, the abandoned Fluvisols presented an average value of 9.33 g kg−1 of OC while the Fluvisols that are currently cultivated have a higher average content of OC (11.35 g kg−1). For soils under industrial use, the average OC content is 5.13 g kg−1. Spatial distribution of organic carbon in these soils depends on the type of soil and the human influence on them, including the use. [ABSTRACT FROM AUTHOR]

This study aimed to establish sound relationships between soil properties of agricultural land in central Spain and their spectral attributes to contribute to deriving an indicator for sustainable farm management. Sixteen plots, managed under various conditions, eight with traditional tillage and eight with other alternative managements, were selected to gather soil samples representing three predominant soil orders (Leptosols, Cambisols, and Luvisols). Soil sampling was conducted from depths ranging from 0 to 30 cm (0–50; 5–10, 10–20, and 20–30 cm), ensuring a broad spectrum of sample variability across different times and locations. The reflectance of soil 64 soil samples was measured within the range of 400 to 900 nm, and the corresponding concentrations of soil organic carbon and majoritarian minerals, calcium carbonate, quartz, phyllosilicates, K-Feldspar, and plagioclase were determined for each sample. Partial least squares analysis was employed to construct prediction models using a calibration dataset comprising 66% of randomly selected samples. The remaining 33% of samples were utilized for model validation. The prediction models for the measured soil chemical properties yielded R2 values ranging from 0.14 to 0.79. Only SOC and limestone provided accurate prediction models. These findings hold promise for developing a soil health indicator tailored for site-specific crop management. However, the complex composition of soil organic carbon and calcium carbonate in certain soils underscores the importance of careful interpretation and validation of remote sensing data, as well as the need for advanced modeling approaches that can account for the interactions between multiple soil constituents. [ABSTRACT FROM AUTHOR]

Abstract Trace element (TE)-contaminated soils require the improvement of their physico-chemical properties in order to allow their restoration through phytostabilization technologies. This study aimed to determine the usefulness of oxidative stress related parameters to validate the suitability of two different combinations of organic (solid fraction of pig slurry) and inorganic (paper mill sludge or a commercial red mud derivative) amendments for the phytostabilization of an acidic (4.2) TE-contaminated mine soil from SE Spain. Two wild species (Silybum marianum and Piptatherum miliaceum) were greenhouse cultivated and the development of the plants, their ionome, and oxidative stress related parameters were determined. Both amendment combinations increased significantly soil pH (to 5–6) and soil/pore water total organic C and total N concentrations, allowing an adequate plant growth and development (plants did not grow in untreated soils). The combination of amendments significantly reduced metal availability and showed to be effective (specially the one including the red mud derivative) in limiting shoot TE concentrations, which were all within common ranges (exclusion based tolerance of these species). Both protein carbonylation and lipid peroxidation were significantly higher in S. marianum plants from phytostabilized soils than in those from non-contaminated soils, which confirms the oxidative stress these plants suffer despite their satisfactory growth in the treated soils. P. miliaceum plants showed no differences between phytostabilized and non-contaminated soils. Therefore, the combination of amendments and TE-tolerant autochthonous species would be a suitable option for the phytostabilisation of soils contaminated by mining activities, reducing TE solubility and allowing an adequate plant growth. Highlights • Solid pig slurry plus inorganic amendments stabilized trace elements in a mine soil. • Milk thistle and smilo grass plants were able to grow well only in amended soil. • Trace element concentrations in the plants were within common ranges for mine soils. • Carbonyl proteins and MDA levels confirmed oxidative stress in milk thistle plants. • Amendments-native species combination suitable for mine soils phytostabilization. [ABSTRACT FROM AUTHOR]

Cave-monitoring studies clarify the climatic, surface vegetation, and karst processes affecting the cave system and lay the foundation for interpreting geochemical stalagmite records. Here we report the monitoring of cave air, bedrock chemistry, and drip water δ13 C DIC , δ18 O, and δ D, as well as 16 trace elements, covering a full annual cycle spanning the 16 months between November 2019 and March 2021 in La Vallina cave in the northwestern Iberian Peninsula. While decreased rainfall and increased evapotranspiration in the summer months lead to a strong reduction in drip rates, there is little seasonal variation in δ18 O and δ D in a given drip, likely reflecting the discrete moderately mixed to well-mixed karst water reservoirs. Small differences in δ18 O and δ D between drip sites are attributed to variable evaporation intensity and/or transit times. The carbon isotope signature of the dissolved inorganic carbon of drip water (δ13 C DIC) is likely driven by seasonal changes in the temperature controlling biological processes (vegetation and microbial soil activity), resulting in minimum δ13 C DIC in summer and autumn months. Increased bedrock dissolution due to higher soil p CO 2 in summer and autumn results in increased trace element concentrations of congruently dissolved elements. Cave air measurements (p CO 2 , δ13 C air , and temperature) indicate the seasonal ventilation (winter) and stagnation (summer) of cave air. The opposite effects of reduced cave air p CO 2 , seasonally variable biological activity, and increased drip rate limit the extent of the seasonal variation in degassing and prior calcite precipitation (PCP) supported by trace elements (Sr/Ca index). Estimated stalagmite growth rates using monitoring data suggest biannual phases of potential calcite precipitation in summer and winter and growth cessation during spring and autumn, depending on cave and drip water conditions and the location within the cave, which has important implications for the proxy interpretation of stalagmite records. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests that warming associated with climate change is decreasing the total amount of soil organic carbon (SOC) in drylands, although scientific research has not given enough emphasis to particulate (POC) and mineral-associated organic carbon (MAOC) pools. Biocrusts are a major biotic feature of drylands and have large impacts on the C cycle, yet it is largely unknown whether they modulate the responses of POC and MAOC to climate change. Here, we assessed the effects of simulated climate change (control, reduced rainfall (RE), warming (WA), and RE + WA) and initial biocrust cover (low (< 20%) versus high (> 50%)) on the mineral protection of soil C and soil organic matter quality in a dryland ecosystem in central Spain for 9 years. At low initial biocrust cover levels, both WA and RE + WA increased SOC, especially POC but also MAOC, and promoted a higher contribution of carbohydrates, relative to aromatic compounds, to the POC fraction. These results suggest that the accumulation of soil C under warming treatments may be transitory in soils with low initial biocrust cover. In soils with high initial biocrust cover, climate change treatments did not affect SOC, neither POC nor MAOC fraction. Overall, our results indicate that biocrust communities modulate the negative effect of climate change on SOC, because no losses of soil C were observed with the climate manipulations under biocrusts. Future work should focus on determining the long-term persistence of the observed buffering effect by biocrust-forming lichens, as they are known to be negatively affected by warming. [ABSTRACT FROM AUTHOR]

Numerous permanent and temporary wetlands occur throughout the world's drylands. Although characterised by diverse water inundation frequencies, durations and depths, these wetlands in drylands are typically hotspots of biological activity and productivity. The healthy functioning and even existence of many wetlands in drylands, however, is threatened by desiccation resulting from a combination of climate change and human disturbance. Near Alcañiz in arid northeast Spain, three adjacent saladas (playas) with contrasting hydroperiods provide an opportunity to investigate how moisture availability affects their soil carbon (C) stocks, CO2 efflux, and microbial communities. Predicting the impacts of changes in moisture availability on the C cycle in wetlands in drylands is challenging but important because many contain large C stocks and may be significant sources and sinks of greenhouse gases. Frequent inundation and/or near-permanent soil water saturation supports the generation of organic C from a range of different sources. Soil inorganic C was greatest on the driest salada (3.8%) compared to the wetter saladas (3.0% and 2.1%) owing to evaporative concentration and the reaction of CO2 with available Ca2+, Mg2+ and Na+ ions. CO2 efflux was greatest at intermediate moisture levels (142 mg CO2 m−2 h−1), but the spatial and temporal variability in CO2 efflux on salada surfaces is large, demonstrating the need for intensive sampling regimes to provide realistic estimates of their contribution to atmospheric CO2 exchanges. Different microbial community structures also characterise each salada. The saladas near Alcañiz, and many other similar features in northeast Spain, are renowned for their rare and threatened flora and fauna, yet their soil C cycle characteristics and soil microbial communities provide additional reasons to monitor the impacts of climate change and protect these vulnerable environments from further anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

Abstract: Irrigated spring cropping systems on sloping soils require conservation agriculture (CA) to minimise soil erosion. In southern Spain, management of residues in the commonly-practiced maize–cotton rotation is a major hurdle against adoption of CA. Recently, a minimal-cultivation, irrigated permanent bed system has been developed in which, two weeks before sowing, maize or cotton residues are relocated from the seed rows on the top of beds into the furrows. This allows solar heating of the beds which accelerates seedling emergence. This paper presents the effects that the introduction of this system had on soil properties along a variably-sloping landscape in which six homogeneous zones were identified. It also discusses the system''s potential for carbon sequestration and shows that a similar quantity of carbon is stored after 4 years under irrigated permanent beds to that after 11–21 years in rainfed no-tillage systems. The relocation of residues resulted on average in lower soil organic carbon concentration (SOCc) in the beds than in the furrows (1.40 and 1.51% respectively in the top 5cm of soil). Under this system SOCc also varied among the landscape zones particularly in the top layers. SOCc was highest in the most eroded shoulder-backslope zone (Z2) though soil organic carbon storage (SOCs) there was the lowest because of the zone''s high >2-mm soil fraction. The SOCs (0–30cm) global average during the study was 35.2MgCha−1 and ranged from 22.4 MgCha−1 in the shoulder Z2 zone to 41.4MgCha−1 in the Z5 footslope zone. When compared to conventionally-managed fields nearby, following this management system appeared to improve soil characteristics significantly and protect against soil erosion. [Copyright &y& Elsevier]

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This study compares the distribution of bulk soil organic carbon (SOC), its fractions (unprotected and physically, chemically, and biochemically protected), available phosphorus (P avail), organic nitrogen (N org), and stable isotope (δ15 N and δ13 C) signatures at four soil depths (0–10, 10–20, 20–30, and 30–40 cm) between a nearby open forest reference area and a historical olive orchard (established in 1856) located in southern Spain. In addition, these soil properties, as well as water stable aggregates (Wsagg), were contrasted at eroding and deposition areas within the olive orchard, previously determined using 137 Cs. SOC stock in the olive orchard (about 40 t C ha -1) was only 25 % of that in the forested area (about 160 t C ha -1) in the upper 40 cm of soil, and the reduction was especially severe in the unprotected organic carbon. The reference and the orchard soils also showed significant differences in the δ13 C and δ15 N signals, likely due to the different vegetation composition and N dynamics in both areas. Soil properties along a catena, from erosion to deposition areas within the old olive orchard, showed large differences. Soil C org , P avail and N org content, and δ15 N at the deposition were significantly higher than those of the erosion area, defining two distinct areas with a different soil quality status. These overall results indicate that the proper understanding of C org content and soil quality in olive orchards requires the consideration of the spatial variability induced by erosion–deposition processes for a convenient appraisal at the farm scale. [ABSTRACT FROM AUTHOR]

A long-term field experiment (1984–2011), was conducted on a Calcic Haploxeralf from semi-arid central Spain to evaluate the combined effect of three treatments: farmyard manure (FYM), straw and control without organic amendments (WOA) and five increasing rates of mineral N on: (1) some energetic parameters of crop production, and (2) the effect of the different treatments on soil organic carbon (SOC) and total N stocks. Crop rotation included spring barley, wheat and sorghum. The energy balance variables considered were net energy produced (energy output minus energy input), the energy output/input ratio and energy productivity (crop yield per unit energy input). Results showed small differences between treatments. Total energy inputs varied from 9.86 GJ ha−1year−1(WOA) to 11.14 GJ ha−1year−1in the FYM system. For the three crops, total energy inputs increased with increasing rates of mineral N. Energy output was slightly lower in the WOA (33.40 GJ ha−1year−1) than in the two organic systems (37.34 and 34.96 GJ ha−1year−1for FYM and straw respectively). Net energy followed a similar trend. At the end of the 27-year period, the stocks of SOC and total N had increased noticeably in the soil profile (0–30 cm) as a result of application of the two organic amendments. Most important SOC changes occurred in the FYM plots, with mean increases in the 0–10 cm depth, amounting an average of 9.9 Mg C ha−1(667 kg C ha−1year−1). Increases in N stocks in the top layer were similar under FYM and straw and ranged from 0.94 to 1.55 Mg N ha−1. By contrast, simultaneous addition of increasing rates of mineral N showed no significant effect on SOC and total N storage. [ABSTRACT FROM AUTHOR]

Aims: Dehesas are agroforestry systems characterized by scattered trees among pastures, crops and/or fallows. A study at a Spanish dehesa has been carried out to estimate the spatial distribution of the soil organic carbon stock and to assess the influence of the tree cover. Methods: The soil organic carbon stock was estimated from the five uppermost cm of the mineral soil with high spatial resolution at two plots with different grazing intensities. The Universal Kriging technique was used to assess the spatial distribution of the soil organic carbon stocks, using tree coverage within a buffering area as an auxiliary variable. Results: A significant positive correlation between tree presence and soil organic carbon stocks up to distances of around 8 m from the trees was found. The tree crown cover within a buffer up to a distance similar to the crown radius around the point absorbed 30 % of the variance in the model for both grazing intensities, but residual variance showed stronger spatial autocorrelation under regular grazing conditions. Conclusions: Tree cover increases soil organic carbon stocks, and can be satisfactorily estimated by means of crown parameters. However, other factors are involved in the spatial pattern of the soil organic carbon distribution. Livestock plays an interactive role together with tree presence in soil organic carbon distribution. [ABSTRACT FROM AUTHOR]

Forests represent an important resource for mitigating the greenhouse effect, but which is the contributions of the different forest types in sequestering and keeping soil C for a longer time is still uncertain, particularly in the Mediterranean area. The aim of this work is to quantify the soil organic C (SOC) stock in the 0-30 and 0-100 cm depths of mineral soil, according to the main forest types-conifers, broadleaf and evergreen broadleaf-and the different climatic zones of Spain, using a database comprising records of 1,974 pedons. Conifers and broadleaf forests show a trend in SOC stock distribution, with the stocks decreasing with increasing Mediterranean conditions. On average, in the 0-30 cm depth, the soils under broadleaf store the highest amount of SOC (5.9 ± 0.1 kg m), followed by conifers (5.6 ± 0.1 kg m) and evergreen broadleaf soils with an amount always lower (3.4 ± 0.2 kg m). Climate and forest cover are the principal factors in determining the amount of SOC stored in Spanish forests. The significantly higher amount of SOC found in conifers and broadleaf forests than the evergreen broadleaf forests leads us to hypothesize a decrease in the SOC if climate change will increase drought periods with a consequent expansion of this latter forest type. Correlations between the SOC stocks under the different forest types, climate and soil features support the major role of climate and vegetation in controlling SOC sequestration in the Mediterranean area, while the effect of texture is less pronounced. Assigning a precise SOC stock to the different forest types, according to each climatic zone, would notably help to obtain an accurate SOC estimate at national level and for future assessments of the status of this large C reservoir. [ABSTRACT FROM AUTHOR]

Contents of soil organic carbon (SOC), gypsum, CaCO3, and quartz, among others, were analyzed and related to reflectance features in visible and near-infrared (VIS/NIR) range, using partial least square regression (PLSR) in ParLes software. Soil samples come from a sloping olive grove managed by frequent tillage in a gypsiferous area of Central Spain. Samples were collected in three different layers, at 0–10, 10–20 and 20–30 cm depth (IPCC guidelines for Greenhouse Gas Inventories Programme in 2006). Analyses were performed by C Loss-On-Ignition, X-ray diffraction and water content by the Richards plates method. Significant differences for SOC, gypsum, and CaCO3 were found between layers; similarly, soil reflectance for 30 cm depth layers was higher. The resulting PLSR models (60 samples for calibration and 30 independent samples for validation) yielded good predictions for SOC (R2 = 0.74), moderate prediction ability for gypsum and were not accurate for the rest of rest of soil components. Importantly, SOC content was related to water available capacity. Soils with high reflectance features held c.a. 40% less water than soils with less reflectance. Therefore, higher reflectance can be related to degradation in gypsiferous soil. The starting point of soil degradation and further evolution could be established and mapped through remote sensing techniques for policy decision making. [ABSTRACT FROM AUTHOR]