Ogano-mineral interactions promote greater soil organic carbon storage under aspen in semi-arid montane forests from Utah

Question: Forest species influence soil organic carbon (SOC) storage through litter input and microclimate, which in interaction with soil texture and mineralogy may lead to differences in SOC stabilization and chemistry. The decline of quacking aspen (Populus tremuloides) and expansion of conifers in the western United States due to natural succession, management practices and climate change could affect SOC dynamics. The objectives of this study were to: (i) assess the effects of overstory composition on SOC storage and stability across the aspen-conifer ecotone, and (ii) characterize the chemical composition of SOC with Fourier transform infrared spectroscopy. Methods: We sampled mineral soil (0-15 cm) across the natural gradient of aspen and mixed conifers stands (Abies lasiocarpa and Pseudotsuga menziesii) in semi-arid montane forests from Utah. SOC was divided into light fraction (LF), mineral-associated SOC in the silt and clay fraction (MoM), and a dense subfraction > 53 µm (SMoM) using wet sieving and electrostatic attraction. SOC decomposability and solubility was derived from long term laboratory incubations and hot water extractions. Mineral matrix samples were obtained by removal of organic matter with NaOCl (6%) at room temperature. We applied Fourier transform infrared spectroscopy to analyze the chemistry of organic matter (OM) (i.e., bulk soil spectra – mineral matrix spectra), LF, and MoM. Results: Vegetation cover did not affect SOC storage (47.0 ± 16.5 Mg C ha−1), SOC decomposability (cumulative CO2-C release of 93.2 ± 65.4 g C g−1 C), or SOC solubility (9.8 ± 7.2 mg C g−1 C), but MoM content increased with presence of aspen [pure aspen (31.2 ± 15.1 Mg C ha-1) > mixed (25.7 ± 8.8 Mg C ha−1) > conifer (22.8 ± 9.0 Mg C ha−1)]. Silt+clay (%) had a positive effect on MoM content (r = 0.64, p < 0.0001), and was negatively correlated to decomposable SOC per gram of C (r = -0.48, p = 0.001) or soluble SOC (r = -0.59, p < 0.0001), indicating that organo-mineral complexes reduced biological availability of SOC. Differences in chemistry among vegetation classes were patent in the LF, with greater proportion of polysaccharides and C-O groups (e.g., esters, phenols, carboxylate) for aspen and mixed LF and greater proportion of aliphatic C for mixed and conifer LF. The same patterns remained in MoM, although the effect of vegetation was statistically significant only for aliphatic C. Conclusions: Our results suggest that aspen dominance favors SOC storage as MoM, although the influence of vegetation may be surpassed by texture in sites with relatively high content of silt and clay (i.e., > 70 %). Management efforts towards the conservation and regeneration of aspen may promote long-term C sequestration in sites with silt + clay content around 40 - 70 %. Greater storage of MoM under aspen may be caused by chemical protection of relatively simple molecules resulting from litter breakdown, fine root turnover, or rhizodeposition, rather than the preservation of recalcitrant compounds (i.e., aliphatic C)

Chemical Composition of Soil Organic Carbon from Mixed Aspen‐Conifer Forests Characterized with Fourier Transform Infrared Spectroscopy

Forest species control the quantity and chemistry of organic matter input, which in interaction with the soil physicochemical properties, environmental conditions and microbial community associated with a given ecosystem may result in specific patterns of soil organic carbon (SOC) stabilization and chemistry. The objectives of this study were: (a) to characterize the chemistry of soil organic matter and SOC fractions across the gradient from pure aspen (Populus tremuloides Michx.) to pure conifer (Abies lasiocarpa (Hook.) Nutt. and Pseudotsuga menziesii (Mirbel) Franco) stands in semi‐arid montane forests, and (b) to determine whether the effect of overstory composition on SOC chemistry was patent beyond the influence of site conditions and microbial decomposer community. We used Fourier transform infrared spectroscopy to analyse the chemistry of bulk soil (BS), light fraction (LF) and mineral‐associated SOC (MoM) from mineral soils (0–15 cm) sampled across the natural gradient of aspen and mixed conifer stands from northern and southern Utah. Vegetation overstory had a subtle effect on the MoM fraction, indicating higher proportion of aliphatic C with aspen dominance, whereas there were no differences in LF chemistry between vegetation types. Independently of the vegetation cover type, the MoM fraction was enriched in aliphatic C compared to the LF, although the proportion of polysaccharides and C‐O groups increased in the MoM fraction for plot samples. Differentiation between spectra from soils developed on sedimentary rock and soils developed on basalt, quartzite and limestone, highlighted the influence of parent material and mineralogy on MoM chemistry. The patterns in SOC fractions\u27 chemistry do not allow an affirmation that greater SOC storage under aspen is due to the accumulation of recalcitrant compounds (i.e., aliphatic C) and controlled by litter chemistry. Rather, they suggest that the ensemble of litter chemistry, microbial community and soil properties in aspen stands enhances SOC storage

Spatial evaluation of the soils capacity and condition to store carbon across Australia

International audienceThe soil security concept has been put forward to maintain and improve soil resources inter alia to provide food, clean water, climate change mitigation and adaptation, and to protect ecosystems. A provisional framework suggested indicators for the soil security dimensions, and a methodology to achieve a quantification. In this study, we illustrate the framework for the function soil carbon storage and the two dimensions of soil capacity and soil condition. The methodology consists of (i) the selection and quantification of a small set of soil indicators for capacity and condition, (ii) the transformation of indicator values to unitless utility values via expert-generated utility graphs, and (iii) a two-level aggregation of the utility values by soil profile and by dimension. For capacity, we used a set of three indicators: total organic and inorganic carbon content and mineral associated organic carbon in the fine fraction (MAOC) estimated via their reference value using existing maps of pedogenons and current landuse to identify areas of remnant genosoils (total organic and inorganic carbon) and the 90th percentile for MAOC. For condition we used the same set of indicators, but this time using the estimated current value and comparing with their reference-state values (calculated for capacity). The methodology was applied to the whole of Australia at a spatial resolution of 90 m x 90 m. The results show that the unitless indicator values supporting the function varied greatly in Australia. Aggregation of the indicators into the two dimensions of capacity and condition revealed that most of Australia has a relatively low capacity to support the function, but that most soils are in a generally good condition relative to that capacity, with some exceptions in agricultural areas, although more sampling of the remnant genosoils is required for corroboration and improvement. The maps of capacity and condition may serve as a basis to estimate a spatially-explicit local index of Australia’s soil resilience to the threat of decarbonization

Grazing, tiling and canopy effects on carbon dioxide fluxes in a Spanish dehesa

There is increasing interest in carbon sequestering capacity of agroforestry systems especially in relation to climate change. Appropriate implementation of silvopastoral practices in dehesa systems may contribute to their sustainability; improve soil carbon (C) and nitrogen (N) storage capacity while reducing the carbon dioxide (CO2) flux from the soil to the atmosphere. The response of soil respiration (Rs) to grazing and tilling practices and trees canopy influence were studied in a dehesa ecosystem in the center of Spain from July 2008 to February 2010. Four different treatments were established: non grazed-non tilled; non grazed-tilled; grazed-non tilled and grazed and tilled. In all the treatments Rs, soil temperature (Ts), soil moisture (Ms), soil C and N stocks were measured. Grazing reduced Rs by 12 % across all experiment. Increments of 3 Mg/ha in C stocks and 0.3 Mg/ha in N stocks in grazing soils were observed. Although, no clear tilling effect on Rs was found, a decrease of 3.5 Mg/ha in soil C stocks and 0.3 Mg/ha in N stocks was detected in tilled soils. Presence of tree canopy induced increases in Rs, soil C and N stocks; while decreases in Ts were observed, but grazing decreased the tree canopy influence on annual C losses by Rs. The Ms constrained the temperature response of Rsduring the experiment, and meaningful Q10 values were only obtainable during the wettest time, ranging from 2.5 to 5.7. Grazing and tree canopy had a positive influence in the ability of soils to store soil C and N, while tilling had a negative effect on soil C and N store capacity in this study. Maintaining the beneficial practices and improving tillage management in this area may have important consequences in carbon sequestration capacity in this dehesa system

Hand-feel soil texture and particle-size distribution in central France. Relationships and implications

International audienceDue to cost constraints, field texture classes estimated by hand-feel by soil surveyors are more abundant than laboratory measurements of particle-size distribution. Thus, there is a considerable potential to use field-estimated soil textures for mapping on the condition that they are reliable and can be characterized by a probability distribution function similar to values obtained by laboratory measurements. This study aimed to investigate and elucidate the differences between the field texture classes estimated by hand-feel and soil texture determined from particle-size analysis under laboratory conditions in a region of Central France. We tested several hypotheses to explain the discrepancies between field estimates and laboratory measurements (organic C content, pH, more detailed particle-size analyses, and CEC). Finally, we simulated the consequences of using particle-size distribution estimated from field texture on a pedotransfer function (PTF) for water retention. Laboratory measurements of clay, silt, and sand content for each field texture class were available for about 17,400 samples. Considering laboratory measurements and the French texture triangle as the reference, the overall accuracy of field texture class allocation was 73%, which was better than most of the results previously reported in the literature. When looking at each field texture class, most predictions were consistent; however, there were noticeable differences between a few field texture classes and particle-size classes. The extreme texture classes located at the corners of the texture triangle were better predicted than those located at the centre of the triangle. We found the discrepancy of field texture classes can be explained by the very fine sand (50–100 µm) and very coarse sand (1000–2000 µm) contents. Based on the particle-size distribution from each field texture class, we calculated their joint probability distribution function of their corresponding laboratory measurements of clay, silt, and sand content. Results showed that PTF values predicted using hand-feel texture were consistent with those obtained with the measured particle-size distribution. Overall, we demonstrated the value of hand-feel texture in expanding the soil texture database and supporting the expansion of the national database to inform soil water retention properties

Drivers and human impacts on topsoil bacterial and fungal community biogeography across Australia

International audienceSoil microbial diversity mediates a wide range of key processes and ecosystem services influencing planetary health. Our knowledge of microbial biogeography patterns, spatial drivers and human impacts at the continental scale remains limited. Here, we reveal the drivers of bacterial and fungal community distribution in Australian topsoils using 1384 soil samples from diverse bioregions. Our findings highlight that climate factors, particularly precipitation and temperature, along with soil properties, are the primary drivers of topsoil microbial biogeography. Using random forest machine‐learning models, we generated high‐resolution maps of soil bacteria and fungi across continental Australia. The maps revealed microbial hotspots, for example, the eastern coast, southeastern coast, and west coast were dominated by Proteobacteria and Acidobacteria. Fungal distribution is strongly influenced by precipitation, with Ascomycota dominating the central region. This study also demonstrated the impact of human modification on the underground microbial community at the continental scale, which significantly increased the relative abundance of Proteobacteria and Ascomycota, but decreased Chloroflexi and Basidiomycota. The variations in microbial phyla could be attributed to distinct responses to altered environmental factors after human modifications. This study provides insights into the biogeography of soil microbiota, valuable for regional soil biodiversity assessments and monitoring microbial responses to global changes

Model averaging for mapping topsoil organic carbon in France

The soil organic carbon (SOC) pool is the largest terrestrial carbon (C) pool and is two to three times larger than the C stored in vegetation and the atmosphere. SOC is a crucial component within the C cycle, and an accurate baseline of SOC is required, especially for biogeochemical and earth system modelling. This baseline will allow better monitoring of SOC dynamics due to land use change and climate change. However, current estimates of SOC stock and its spatial distribution have large uncertainties. In this study, we test whether we can improve the accuracy of the three existing SOC maps of France obtained at national (IGCS), continental (LUCAS), and global (SoilGrids) scales using statistical model averaging approaches. Soil data from the French Soil Monitoring Network (RMQS) were used to calibrate and evaluate five model averaging approaches, i.e., Granger-Ramanathan, Bias-corrected Variance Weighted (BC-VW), Bayesian Modelling Averaging, Cubist and Residual-based Cubist. Cross-validation showed that with a calibration size larger than 100 observations, the five model averaging approaches performed better than individual SOC maps. The BC-VW approach performed best and is recommended for model averaging. Our results show that 200 calibration observations were an acceptable calibration strategy for model averaging in France, showing that a fairly small number of spatially stratified observations (sampling density of 1 sample per 2500 km2) provides sufficient calibration data. We also tested the use of model averaging in data-poor situations by reproducing national SOC maps using various sized subsets of the IGCS dataset for model calibration. The results show that model averaging always performs better than the national SOC map. However, the Modelling Efficiency dropped substantially when the national SOC map was excluded in model averaging. This indicates the necessity of including a national SOC map for model averaging, even if produced with a small dataset (i.e., 200 samples). This study provides a reference for data-poor countries to improve national SOC maps using existing continental and global SOC maps.</p

A proposal for the assessment of soil security: Soil functions, soil services and threats to soil

Human societies face six existential challenges to their sustainable development. These challenges have been previously addressed by a myriad of concepts such as soil conservation, soil quality, and soil health. Yet, of these, only soil security attempts to integrate the six existential challenges concurrently through the five biophysical and socio-economic dimensions of capacity, condition, capital, connectivity and codification. In this paper, we highlight past and existing concepts, and make a proposal for a provisional assessment of soil security. The proposal addresses three roles of soil: soil functions, soil services and threats to soil. For each identified role, we indicate a potential, but not exhaustive, list of indicators that characterise the five dimensions of soil security. We also raise issues of quantification and combination of indicators briefly. We found that capacity and condition are theoretically easier to measure and quantify than connectivity and codification. The dimension capital might be conveniently assessed using indicators that relate to the economic value of soils. The next step is to test this proposal for which we make recommendations on potential study cases and examples. We conclude that the five dimensions of soil security can potentially be assessed quantitatively and comprehensively using indicators that characterise each role, but also found that there is need for further work to devise an operational measurement methodology to estimate connectivity of people to soil

Current NPP cannot predict future soil organic carbon sequestration potential. Comment on “Photosynthetic limits on carbon sequestration in croplands”

International audienc

Comprender la gestión de la autonomía de los centros escolares

Comprender la problemática de la autonomía escolar y su vinculación práctica, especialmente, con la calidad de la enseñanza. Por una parte, agentes internos (dirección y equipo directivo, docentes, coordinadores de ciclo y jefes de departamentos, padres y madres y el psicopedagogo) y, por otra, agentes externos (inspección, asesores del CEP y equipos de orientación educativa). Todos ellos de centros educativos de Primaria y Secundaria situados en las provincias de Cádiz, Sevilla y Málaga. Se realizó un total de 85 entrevistas semi-estructuradas a los diversos agentes y se organizaron seis grupos de discusión, tres compuestos por agentes externos e internos y otros tres formados por alumnado de Secundaria. 1. La autonomía escolar debe ser concebida teniendo en cuenta los contextos sociales, culturales y económicos de los centros. Aunque no se puede afirmar que tenga una relación causal con la calidad de la enseñanza, sí que es una pieza clave de la misma. 2. Para el desarrollo de la autonomía, la forma más adecuada es el liderazgo entendido como dinamización y como dinámica del grupo, donde se conjuguen elementos tales como la confianza y la responsabilidad, la flexibilidad, la conjunción sistemática y la transparencia. 3. En cuanto a la percepción del papel de la Administración, se entiende que es una institución ausente, intransigente, desconfiada y controladora. Los centros se sienten dominados por la burocracia, y las acciones de la Administración no parecen potenciar su autonomía. 4. La cultura individualista está muy asentada entre el profesorado, aunque comienzan a extenderse prácticas relacionadas con una cultura participativa centrada en la colaboración, la coordinación y el trabajo en grupo. 5. La autonomía exige mejores recursos y una adecuada administración de los mismos, lo que no supone aumentar considerablemente los gastos y presupuestos, sino alcanzar los mínimos desde los cuales y con los cuales los centros pueden plantearse orientar sus acciones hasta la autonomía. Esta investigación no está cerrada, sino que permanece abierta. Se podría indagar, a través de Estudios de Casos, la presencia del liderazgo en los centros, la presencia de diversas culturas individualistas, la aparición de rasgos de la cultura de la colegialidad, y a través de Cuestionarios, opiniones sobre la escolaridad, sobre el papel de la administración, y sobre los recursos escolares.Ministerio Educación CIDEBiblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5 - 3 Planta; 28014 Madrid; Tel. +34917748000; Fax +34917748026; [email protected]