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Carlos M Regalado - One of the best experts on this subject based on the ideXlab platform.
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performance of the commercial wet capacitance sensor as compared with time domain reflectometry in Volcanic Soils
Vadose Zone Journal, 2007Co-Authors: Carlos M Regalado, Axel Ritter, Rosa M RodriguezgonzalezAbstract:Among different alternatives, dielectric capacitance sensors may provide simultaneous readings of the volumetric water content and the soil solution electrical conductivity in the same sample volume at low cost. Reliability of capacitive sensors may be questioned, however, due to the low signal frequency at which they work, and also because of soil electrical conductivity effects on the water content estimation. In this study we evaluated the commercial capacitive WET Sensor (Delta-T Devices Ltd., Burwell, UK) compared with time domain reflectometry (TDR) in three Volcanic Soils with different textures. Although the WET Sensor uses internally the Hilhorst approach for describing the relationship between soil moisture and bulk and pore water electrical conductivity, results suggest that the Vogeler model is a better choice for the Soils studied. The sensor provides good estimation of the bulk electrical conductivity, but determination of soil water content is biased. Thus, we propose an alternative empirical equation to determine the volumetric water content from the WET Sensor readings, the soil bulk density, and an estimate of the sensor's effective frequency.
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Using TDR and Inverse Modeling to Characterize Solute Transport in a Layered Agricultural Volcanic Soil
Vadose Zone Journal, 2005Co-Authors: Axel Ritter, Carlos M Regalado, Rafael Muñoz-carpena, Mathieu Javaux, Marnik VancloosterAbstract:Volcanic Soils exhibit particular physical-chemical properties (i.e., strong and stable natural aggregation and high content of variable-charge minerals) that may influence solute transport. To determine if such techniques like TDR and inverse modeling are useful for analyzing solute transport in Volcanic Soils, we studied the governing transport processes by means of a miscible displacement experiment of Br- in a large undisturbed soil monolith. Bromide resident concentrations at several depths were monitored successfully with TDR technology, while parameters for the convective - dispersive (CDE) and mobile immobile (MIM) transport models were estimated by inverse modeling. For the relatively high soil moisture conditions, typical of high frequency-irrigation systems that we considered, Br- was found to move slowly by convection - dispersion. Simulations with the CDE and MIM transport models yielded very similar results. Although Br- is generally assumed to behave as a tracer, we found that anion in our experiment was subject to adsorption at the bottom of the monolith. This may be explained by the variable-charge nature of the minerals Fe and Al oxihydroxides) present in this Volcanic soil, which exhibited anion exchange when the pH of the soil solution decreased below the zero point of charge
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a physical interpretation of logarithmic tdr calibration equations of Volcanic Soils and their solid fraction permittivity based on lichtenecker s mixing formulae
Geoderma, 2004Co-Authors: Carlos M RegaladoAbstract:Abstract A physical interpretation of both logarithmic Time Domain Reflectometry (TDR) calibration equations and empirical estimates of the solid fraction permittivity of Volcanic Soils is given in terms of the power-law mixing formulae e eff α = ∑ i=1 N f i e i α . It is shown that, for most of the moisture range, the logarithmic Lichtenecker's law (α=0) may hold in Volcanic Soils, while for coarse mineral Soils a Birchak model (α=1/2) may be universally valid. Two distinct logarithmic dielectric regimes dominated by free and bound water were identified for at least some Soils. Such a transition from high to low water content may be predicted from the wilting point of the soil. At very low water content Lichtenecker's formula breaks down in Volcanic Soils, and a Birchak refractive index model results are more appropriate. The latter provides a generalization and physical interpretation of previous empirical estimates of the permittivity of the mineral fraction of Soils, es, and it permits the estimation of es in Volcanic Soils from dry soil samples packed in air, where previous estimates (developed for mineral Soils) failed to do so.
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time domain reflectometry models as a tool to understand the dielectric response of Volcanic Soils
Geoderma, 2003Co-Authors: Carlos M Regalado, Munoz R Carpena, A R Socorro, J Hernandez M MorenoAbstract:The transmission of an electromagnetic wave through the soil using time domain reflectometry (TDR) permits the determination of its water content, h, given the composite dielectric constant of the soil, ec, via Topp’s equation. This is possible since the dielectric constant of water is much larger than that of the soil’s solid phase (80 vs. 5) and, therefore, changes in soil moisture content lead to variations in ec. However, organic Soils and those of Volcanic origin do not obey the ‘‘universal’’ relationship ec–h originally obtained by Topp. Hence, several authors have proposed alternative empirical ec–h relationships. Volcanic Soils are particular with respect to their low bulk density, large porosity and specific surface, mainly due to the strong aggregation of particles and high concentration of Fe-oxihydroxides, and also due to the presence of allophanic clays with large surface area and water affinity. Thus, it is likely that the water retention characteristics of Volcanic Soils will exhibit an atypical dielectric behaviour. This work shows that physical models, which incorporate parameters such as bulk density, porosity and surface area, can interpret the anomalous dielectric behaviour of Volcanic Soils. Among these models, we shall distinguish those which consider three phases (water–air–soil) and those which separate the water content in two phases, i.e. free and bound water (four-phase models). Four-phase models help identify two distinct linear dielectric regimes dominated by free and bound water, respectively, for at least some Soils. Soil porosity is shown to play an important role in the dielectric behaviour of Volcanic Soils. We also found that soil andic parameters provide an a priori diagnosis criterion to evaluate the departure of Volcanic Soils from Topp’s curve. Additionally, we propose an alternative general ec–h calibration relationship for these kinds of Soils, which may be incorporated in commercial TDR devices for laboratory and field water content determination. D 2003 Elsevier Science B.V. All rights reserved.
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Physical properties of “sorriba”-cultivated Volcanic Soils from Tenerife in relation to andic diagnostic parameters
Geoderma, 2003Co-Authors: S. Armas-espinel, J.m. Hernández-moreno, Rafael Muñoz-carpena, Carlos M RegaladoAbstract:In Volcanic regions, Soils containing both noncrystalline materials and layer silicates are widespread. Although the respective contribution of these components to soil physical behaviours is difficult to quantify, it is an important issue in the Canary Islands, where Andisols and andic Soils are transported to the low lands for cultivation (‘‘sorriba’’). In this new soil environment, salinisation and sodification processes, induced by irrigation and heavy fertilisation, are potential threats to soil degradation. The purpose of this work was to evaluate some relevant physical properties of the sorriba-cultivated Volcanic Soils from Tenerife in order to relate them to salinity and sodicity soil conditions, amounts of layer silicates and remaining andic properties, characterised by: bulk density (qb), Al and Fe extracted with ammonium oxalate (Alo ,F eo) and P retention. An Andisol under forest was included in the study as a representative natural reference. Clay dispersion, water release curves and saturated hydraulic conductivity, Ks, were the selected physical properties. Four distinctive types of water release curves were identified, showing sandy behaviour at low suctions while retaining large water holding capacity at large suctions. The van Genuchten parameters helped to differentiate these curves and identify the main pore-size ranges. Under certain combinations of exchangeable cations distribution, salinity and clay mineralogy, very low Ks values were observed for Alo contents lower than 3%. The results suggest that the aggregating effect of Alo (allophanes) could not counterbalance soil structure deterioration. Furthermore, only a multivariable analysis carried out on chemistry, mineralogy and physical data had the merit to classify the studied sorriba-cultivated Volcanic Soils in terms of soil quality and soil functioning. D 2003 Elsevier Science B.V. All rights reserved.
Irwin M Umami - One of the best experts on this subject based on the ideXlab platform.
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land use and management effects on Volcanic Soils in west sumatra indonesia
Geoderma Regional, 2020Co-Authors: Susumu S Abe, Kenta Ashida, Maulana I Kamil, Keisuke Tobisaka, Khairun N Kamarudin, Irwin M UmamiAbstract:Abstract In this study, we aimed to assess the influence of land use and management on the fertility characteristics and pedogenic indicators of Volcanic Soils. Our study area was a mountainous area located in West Sumatra, Indonesia, where local farmers intensively cultivate vegetables by applying high amounts of chemical fertilizers and agrochemicals. Some negative impacts of conventional management were observed in the vegetable fields: soil acidification and loss of organic matter, with descended soil pH and increased acidity as well as decreased contents of exchangeable bases and with decreased amount of organic C. These impacts were not effectively mitigated by positive factors such as increased P availability and decreased capacity for P fixation. Continued cultivation over the years compounded the effects of these changes. Organic farming was advantageous in terms of soil fertility maintenance as it alleviated negative impacts compared to conventional farming. Natural fallow was effective in replenishing soil fertility as indicated by a significant increase in organic C, total N, and exchangeable Ca and Mg contents compared to the vegetable fields. The degree of replenishment was enhanced with a longer period under fallow; however, the natural fallow decreased P availability and increased P fixation capacity. Calliandra calothyrsus fallow further accelerated soil acidification, regardless of the rapid increase in the organic C and exchangeable bases contents. The adverse effects of Calliandra fallow were associated with the formation of humus–aluminum complexes to an extent that it changed from Sil-andic to Alu-andic Andosols.
J.l. Mora - One of the best experts on this subject based on the ideXlab platform.
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Factors affecting CO2 efflux rates and the stability of soil organic carbon storage in Volcanic Soils of the Canary Islands
Mitigation and Adaptation Strategies for Global Change, 2014Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:Because Volcanic Soils store large amounts of soil organic carbon (SOC), they play a far more important role in the carbon (C) cycle than their limited global coverage suggests. We analysed the C released as CO2 from a range of Volcanic Soils under natural conditions and analysed the influence of environmental variables (moisture and temperature), substrate availability (as assessed from the contents of various SOC fractions and the inputs of plant residues from litterfall), respiratory agents (roots, microorganisms and decomposing enzymes) and other pedological features of the topSoils (0–30 cm depth) on the CO2 efflux rates over a 2-year experimental period. High CO2 efflux rates (419 g C-CO2 m−2 y−1 as the average for Andisols) were obtained that were related to significant decreases in the amount of SOC stored. CO2 release was strongly controlled by soil moisture, although it was inhibited in the Andisols with the highest moisture levels (above 50 kg m−2 in topsoil). It was not responsive to the availability of decomposing microorganisms or enzymes and appeared more related to the inputs of easily decomposable plant residues than to the amount of either labile or recalcitrant SOC. Among the SOC pools, only the water-soluble C in saturated paste extracts (WSCse) of air-dried soil samples was consistently correlated with the CO2 efflux rates. The desiccation of Andisols appeared to induce the release of previously stabilised SOC, which was readily mineralised when the moisture conditions became favourable. The results of this study indicate that SOC storage in Andisols is highly vulnerable to drying-wetting processes even in unmanaged natural ecosystems and that microclimate conditions can be critical for successful C sequestration in these Soils.
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Storage and depth distribution of organic carbon in Volcanic Soils as affected by environmental and pedological factors
CATENA, 2014Co-Authors: J.l. Mora, C. D. Arbelo, J. A. Guerra, Cecilia Armas Herrera, A. Rodriguez-rodriguezAbstract:It has been recognised that Volcanic Soils, particularly Andosols, can store large amounts of soil organic carbon (SOC). This study investigates the factors controlling the regional and vertical distributions of SOC in Soils of Volcanic origin. To this aim, we investigated the vertical distribution of SOC in a total of 212 soil profiles representing all combinations of soil-forming factors in a Volcanic area with a high diversity of ecosystems and soil types. We analysed the SOC contents in relation to intrinsic (soil type and relevant soil properties: texture and pH) and extrinsic factors (climate, parent material, relief), and we studied the patterns of SOC distribution with depth by fitting the SOC contents to different curve models. Furthermore, we selected ten soil profiles for a more detailed study to assess the effect of vegetation by examining the relationships of the SOC storage and depth distribution to the amount and allocation of plant roots and litterfall. SOC storage was controlled by the interaction of climatic (rainfall), time (substrate age), topographic (slope) and biotic (plant-mediated) factors. Our results indicate that under humid conditions, large organic inputs and the inhibition of microbial degradation due to low pH, AI-toxicity and persistent anaerobiosis within soil microaggregates largely contributed to SOC accumulation. Soil type was a poor predictor of SOC storage, most likely due to the co-occurrence of young and evolved Andosols and a certain andic character in many Soils that did not qualify as Andosols. The distributions of root carbon and SOC appeared to be closely interrelated, suggesting a major role of roots in the supply of organic matter and the lack of significant bioturbation. The depth distribution of SOC was best fitted by the quadratic, cubic and power models, the latter being a feasible alternative that should be used to this aim in Volcanic Soils rather than the widely used exponential model.
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Interannual variations of soil organic carbon fractions in unmanaged Volcanic Soils (Canary Islands, Spain).
Ecology and evolution, 2012Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:The stability over time of the organic C stocked in Soils under undisturbed ecosystems is poorly studied, despite being suitable for detecting changes related to climate fluctuations and global warming. Volcanic Soils often show high organic C contents due to the stabilization of organic matter by short-range ordered minerals or Al-humus complexes. We investigated the dynamics of different organic C fractions in Volcanic Soils of protected natural ecosystems of the Canary Islands (Spain) to evaluate the stability of their C pools. The study was carried out in 10 plots, including both undisturbed and formerly disturbed ecosystems, over two annual periods. C inputs to (litterfall) and outputs from (respiration) the soil, root C stocks (0–30 cm), soil organic C (SOC) fractions belonging to C pools with different degrees of biogeochemical stability –total oxidisable C (TOC), microbial biomass C (MBC), water soluble C (WSC), hot-water extractable C (HWC), humic C (HSC), – and total soil N (TN) (at 0–15 and 15–30 cm) were measured seasonally.A statistically significant interannual increase in CO2 emissions and a decrease in the SOC, mainly at the expense of the most labile organic forms, were observed, while the root C stocks and litterfall inputs remained relatively constant over the study period. The observed changes may reflect an initial increase in SOC resulting from low soil respiration rates due to drought during the first year of study. The Soils of nearly mature ecosystems were more apparently affected by C losses, while those undergoing the process of active natural regeneration exhibited disguised C loss because of the C sequestration trend that is characteristic of progressive ecological succession.
Antonio Rodríguez-rodríguez - One of the best experts on this subject based on the ideXlab platform.
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Effectiveness of Polyacrylamide, Wood Shred Mulch, and Pine Needle Mulch as Post-Fire Hillslope Stabilization Treatments in Two Contrasting Volcanic Soils
Forests, 2017Co-Authors: Jonay Neris, C. D. Arbelo, Stefan H. Doerr, Jesús Santiago Notario Del Pino, Antonio Rodríguez-rodríguezAbstract:Post-fire hillslope stabilization treatments aim to reduce runoff-erosion risks following forest fires by counteracting the impact of fire on key soil and hillslope properties. Here we evaluate the effectiveness of wood shred mulch, long-leaved pine needle mulch, and polyacrylamide (PAM) in reducing post-fire runoff and erosion in two Volcanic soil types of contrasting wettability using rainfall simulations (55 mm h−1 for 30 min) at the microplot (0.25 m2) scale. The cover provided by the wood shreds and pine needles led to a reduction of runoff and erosion in both the wettable—(62% and 92%, respectively, for wood shreds, and 55% and 87%, respectively, for needle mulch) and the extremely water-repellent Soils (44% and 61%, respectively, for wood shreds). In contrast to what might be expected, PAM did not reduce runoff or erosion when applied to the extremely water-repellent Soils, suggesting that PAM should not be applied in this terrain type. Although more research is needed to determine whether the high effectiveness of pine needle mulch and wood shred mulch fully translates to coarser scales, the results are encouraging in terms of these materials’ ability to provide effective and relatively economic mitigation treatments for fire-induced runoff-erosion risks in Volcanic Soils.
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Factors affecting CO2 efflux rates and the stability of soil organic carbon storage in Volcanic Soils of the Canary Islands
Mitigation and Adaptation Strategies for Global Change, 2014Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:Because Volcanic Soils store large amounts of soil organic carbon (SOC), they play a far more important role in the carbon (C) cycle than their limited global coverage suggests. We analysed the C released as CO2 from a range of Volcanic Soils under natural conditions and analysed the influence of environmental variables (moisture and temperature), substrate availability (as assessed from the contents of various SOC fractions and the inputs of plant residues from litterfall), respiratory agents (roots, microorganisms and decomposing enzymes) and other pedological features of the topSoils (0–30 cm depth) on the CO2 efflux rates over a 2-year experimental period. High CO2 efflux rates (419 g C-CO2 m−2 y−1 as the average for Andisols) were obtained that were related to significant decreases in the amount of SOC stored. CO2 release was strongly controlled by soil moisture, although it was inhibited in the Andisols with the highest moisture levels (above 50 kg m−2 in topsoil). It was not responsive to the availability of decomposing microorganisms or enzymes and appeared more related to the inputs of easily decomposable plant residues than to the amount of either labile or recalcitrant SOC. Among the SOC pools, only the water-soluble C in saturated paste extracts (WSCse) of air-dried soil samples was consistently correlated with the CO2 efflux rates. The desiccation of Andisols appeared to induce the release of previously stabilised SOC, which was readily mineralised when the moisture conditions became favourable. The results of this study indicate that SOC storage in Andisols is highly vulnerable to drying-wetting processes even in unmanaged natural ecosystems and that microclimate conditions can be critical for successful C sequestration in these Soils.
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Interannual variations of soil organic carbon fractions in unmanaged Volcanic Soils (Canary Islands, Spain).
Ecology and evolution, 2012Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:The stability over time of the organic C stocked in Soils under undisturbed ecosystems is poorly studied, despite being suitable for detecting changes related to climate fluctuations and global warming. Volcanic Soils often show high organic C contents due to the stabilization of organic matter by short-range ordered minerals or Al-humus complexes. We investigated the dynamics of different organic C fractions in Volcanic Soils of protected natural ecosystems of the Canary Islands (Spain) to evaluate the stability of their C pools. The study was carried out in 10 plots, including both undisturbed and formerly disturbed ecosystems, over two annual periods. C inputs to (litterfall) and outputs from (respiration) the soil, root C stocks (0–30 cm), soil organic C (SOC) fractions belonging to C pools with different degrees of biogeochemical stability –total oxidisable C (TOC), microbial biomass C (MBC), water soluble C (WSC), hot-water extractable C (HWC), humic C (HSC), – and total soil N (TN) (at 0–15 and 15–30 cm) were measured seasonally.A statistically significant interannual increase in CO2 emissions and a decrease in the SOC, mainly at the expense of the most labile organic forms, were observed, while the root C stocks and litterfall inputs remained relatively constant over the study period. The observed changes may reflect an initial increase in SOC resulting from low soil respiration rates due to drought during the first year of study. The Soils of nearly mature ecosystems were more apparently affected by C losses, while those undergoing the process of active natural regeneration exhibited disguised C loss because of the C sequestration trend that is characteristic of progressive ecological succession.
C. D. Arbelo - One of the best experts on this subject based on the ideXlab platform.
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Effectiveness of Polyacrylamide, Wood Shred Mulch, and Pine Needle Mulch as Post-Fire Hillslope Stabilization Treatments in Two Contrasting Volcanic Soils
Forests, 2017Co-Authors: Jonay Neris, C. D. Arbelo, Stefan H. Doerr, Jesús Santiago Notario Del Pino, Antonio Rodríguez-rodríguezAbstract:Post-fire hillslope stabilization treatments aim to reduce runoff-erosion risks following forest fires by counteracting the impact of fire on key soil and hillslope properties. Here we evaluate the effectiveness of wood shred mulch, long-leaved pine needle mulch, and polyacrylamide (PAM) in reducing post-fire runoff and erosion in two Volcanic soil types of contrasting wettability using rainfall simulations (55 mm h−1 for 30 min) at the microplot (0.25 m2) scale. The cover provided by the wood shreds and pine needles led to a reduction of runoff and erosion in both the wettable—(62% and 92%, respectively, for wood shreds, and 55% and 87%, respectively, for needle mulch) and the extremely water-repellent Soils (44% and 61%, respectively, for wood shreds). In contrast to what might be expected, PAM did not reduce runoff or erosion when applied to the extremely water-repellent Soils, suggesting that PAM should not be applied in this terrain type. Although more research is needed to determine whether the high effectiveness of pine needle mulch and wood shred mulch fully translates to coarser scales, the results are encouraging in terms of these materials’ ability to provide effective and relatively economic mitigation treatments for fire-induced runoff-erosion risks in Volcanic Soils.
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Factors affecting CO2 efflux rates and the stability of soil organic carbon storage in Volcanic Soils of the Canary Islands
Mitigation and Adaptation Strategies for Global Change, 2014Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:Because Volcanic Soils store large amounts of soil organic carbon (SOC), they play a far more important role in the carbon (C) cycle than their limited global coverage suggests. We analysed the C released as CO2 from a range of Volcanic Soils under natural conditions and analysed the influence of environmental variables (moisture and temperature), substrate availability (as assessed from the contents of various SOC fractions and the inputs of plant residues from litterfall), respiratory agents (roots, microorganisms and decomposing enzymes) and other pedological features of the topSoils (0–30 cm depth) on the CO2 efflux rates over a 2-year experimental period. High CO2 efflux rates (419 g C-CO2 m−2 y−1 as the average for Andisols) were obtained that were related to significant decreases in the amount of SOC stored. CO2 release was strongly controlled by soil moisture, although it was inhibited in the Andisols with the highest moisture levels (above 50 kg m−2 in topsoil). It was not responsive to the availability of decomposing microorganisms or enzymes and appeared more related to the inputs of easily decomposable plant residues than to the amount of either labile or recalcitrant SOC. Among the SOC pools, only the water-soluble C in saturated paste extracts (WSCse) of air-dried soil samples was consistently correlated with the CO2 efflux rates. The desiccation of Andisols appeared to induce the release of previously stabilised SOC, which was readily mineralised when the moisture conditions became favourable. The results of this study indicate that SOC storage in Andisols is highly vulnerable to drying-wetting processes even in unmanaged natural ecosystems and that microclimate conditions can be critical for successful C sequestration in these Soils.
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Storage and depth distribution of organic carbon in Volcanic Soils as affected by environmental and pedological factors
CATENA, 2014Co-Authors: J.l. Mora, C. D. Arbelo, J. A. Guerra, Cecilia Armas Herrera, A. Rodriguez-rodriguezAbstract:It has been recognised that Volcanic Soils, particularly Andosols, can store large amounts of soil organic carbon (SOC). This study investigates the factors controlling the regional and vertical distributions of SOC in Soils of Volcanic origin. To this aim, we investigated the vertical distribution of SOC in a total of 212 soil profiles representing all combinations of soil-forming factors in a Volcanic area with a high diversity of ecosystems and soil types. We analysed the SOC contents in relation to intrinsic (soil type and relevant soil properties: texture and pH) and extrinsic factors (climate, parent material, relief), and we studied the patterns of SOC distribution with depth by fitting the SOC contents to different curve models. Furthermore, we selected ten soil profiles for a more detailed study to assess the effect of vegetation by examining the relationships of the SOC storage and depth distribution to the amount and allocation of plant roots and litterfall. SOC storage was controlled by the interaction of climatic (rainfall), time (substrate age), topographic (slope) and biotic (plant-mediated) factors. Our results indicate that under humid conditions, large organic inputs and the inhibition of microbial degradation due to low pH, AI-toxicity and persistent anaerobiosis within soil microaggregates largely contributed to SOC accumulation. Soil type was a poor predictor of SOC storage, most likely due to the co-occurrence of young and evolved Andosols and a certain andic character in many Soils that did not qualify as Andosols. The distributions of root carbon and SOC appeared to be closely interrelated, suggesting a major role of roots in the supply of organic matter and the lack of significant bioturbation. The depth distribution of SOC was best fitted by the quadratic, cubic and power models, the latter being a feasible alternative that should be used to this aim in Volcanic Soils rather than the widely used exponential model.
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Interannual variations of soil organic carbon fractions in unmanaged Volcanic Soils (Canary Islands, Spain).
Ecology and evolution, 2012Co-Authors: C. M. Armas-herrera, J.l. Mora, C. D. Arbelo, Antonio Rodríguez-rodríguezAbstract:The stability over time of the organic C stocked in Soils under undisturbed ecosystems is poorly studied, despite being suitable for detecting changes related to climate fluctuations and global warming. Volcanic Soils often show high organic C contents due to the stabilization of organic matter by short-range ordered minerals or Al-humus complexes. We investigated the dynamics of different organic C fractions in Volcanic Soils of protected natural ecosystems of the Canary Islands (Spain) to evaluate the stability of their C pools. The study was carried out in 10 plots, including both undisturbed and formerly disturbed ecosystems, over two annual periods. C inputs to (litterfall) and outputs from (respiration) the soil, root C stocks (0–30 cm), soil organic C (SOC) fractions belonging to C pools with different degrees of biogeochemical stability –total oxidisable C (TOC), microbial biomass C (MBC), water soluble C (WSC), hot-water extractable C (HWC), humic C (HSC), – and total soil N (TN) (at 0–15 and 15–30 cm) were measured seasonally.A statistically significant interannual increase in CO2 emissions and a decrease in the SOC, mainly at the expense of the most labile organic forms, were observed, while the root C stocks and litterfall inputs remained relatively constant over the study period. The observed changes may reflect an initial increase in SOC resulting from low soil respiration rates due to drought during the first year of study. The Soils of nearly mature ecosystems were more apparently affected by C losses, while those undergoing the process of active natural regeneration exhibited disguised C loss because of the C sequestration trend that is characteristic of progressive ecological succession.
