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SoilGrids produces maps of soil properties for the entire globe at medium spatial resolution (250 m cell size) using state-of-the-art machine learning methods to generate the necessary models. It takes as inputs soil observations from about 240 000 locations worldwide and over 400 global environmental covariates describing vegetation, terrain morphology, climate, geology and hydrology. The aim of this work was the production of global maps of soil properties, with cross-validation, hyper-parameter selection and quantification of spatially explicit uncertainty, as implemented in the SoilGrids version 2.0 product incorporating state-of-the-art practices and adapting them for global digital soil mapping with legacy data. The paper presents the evaluation of the global predictions produced for soil organic carbon content, total nitrogen, coarse fragments, pH (water), cation exchange capacity, bulk density and texture fractions at six standard depths (up to 200 cm). The quantitative evaluation showed metrics in line with previous global, continental and large-region studies. The qualitative evaluation showed that coarse-scale patterns are well reproduced. The spatial uncertainty at global scale highlighted the need for more soil observations, especially in high-latitude regions.

Developing urbanization, water shortage, watercourse pollution, and demands for more food due to population growth require a more efficient water irrigation and fertilizer application. Retaining nutrients and water in agricultural soils brings about higher crop yields and prevents pollution of water courses. Among different solutions, zeolites, which are environmental friendly, ubiquitous, and inexpensive, have been extensively employed in agricultural activities. These minerals are considered as soil conditioners to improve soil physical and chemical properties including infiltration rate, saturated hydraulic conductivity ( K s ), water holding capacity (WHC), and cation exchange capacity (CEC). Natural and surface-modified zeolites can efficiently hold water and nutrients including ammonium (NH 4 + ), nitrate (NO 3 − ) and phosphate (PO 4 3− ), potassium (K + ), and sulfate (SO 4 2− ) in their unique porous structures. Their application as slow-release fertilizers (SRFs) are reported as well. Therefore, zeolite application can improve both water use efficiency (WUE) and nutrient use efficiency (NUE) in agricultural activities and consequently can reduce the potential of surface and groundwater pollution. This review paper summarizes findings in the literature about the impact of zeolite applications on water and nutrient retention in the agriculture. Furthermore, it explores benefits and drawbacks of zeolite applications in this regard. Graphical Abstract ᅟ

PurposeForests play a critical role in terrestrial ecosystem carbon cycling and the mitigation of global climate change. Intensive forest management and global climate change have had negative impacts on the quality of forest soils via soil acidification, reduction of soil organic carbon content, deterioration of soil biological properties, and reduction of soil biodiversity. The role of biochar in improving soil properties and the mitigation of greenhouse gas (GHG) emissions has been extensively documented in agricultural soils, while the effect of biochar application on forest soils remains poorly understood. Here, we review and summarize the available literature on the effects of biochar on soil properties and GHG emissions in forest soils.Materials and methodsThis review focuses on (1) the effect of biochar application on soil physical, chemical, and microbial properties in forest ecosystems; (2) the effect of biochar application on soil GHG emissions in forest ecosystems; and (3) knowledge gaps concerning the effect of biochar application on biogeochemical and ecological processes in forest soils.Results and discussionBiochar application to forests generally increases soil porosity, soil moisture retention, and aggregate stability while reducing soil bulk density. In addition, it typically enhances soil chemical properties including pH, organic carbon stock, cation exchange capacity, and the concentration of available phosphorous and potassium. Further, biochar application alters microbial community structure in forest soils, while the increase of soil microbial biomass is only a short-term effect of biochar application. Biochar effects on GHG emissions have been shown to be variable as reflected in significantly decreasing soil N2O emissions, increasing soil CH4 uptake, and complex (negative, positive, or negligible) changes of soil CO2 emissions. Moreover, all of the aforementioned effects are biochar-, soil-, and plant-specific.ConclusionsThe application of biochars to forest soils generally results in the improvement of soil physical, chemical, and microbial properties while also mitigating soil GHG emissions. Therefore, we propose that the application of biochar in forest soils has considerable advantages, and this is especially true for plantation soils with low fertility.

PurposeThe majority of biochar studies use soils with only a narrow range of properties making generalizations about the effects of biochar on soils difficult. In this study, we aimed to identify soil properties that determine the performance of biochar produced at high temperature (700 °C) on soil pH, cation exchange capacity (CEC), and exchangeable base cation (Ca2+, K+, and Mg2+) content across a wide range of soil physicochemical properties.Materials and methodsTen distinct soils with varying physicochemical properties were incubated for 12 weeks with four rates of biochar application (0.5, 2, 4, and 8% w/w). Soil pH, CEC, and exchangeable base cations (Ca2+, K+, and Mg2+) were determined on the 7th and 84th day of incubation.Results and discussionOur results indicate that the highest biochar application rate (8%) was more effective at altering soil properties than lower biochar rates. Application of 8% biochar increased pH significantly in all incubated soils, with the increment ranging up to 1.17 pH unit. Biochar induced both an increment and a decline in soil CEC ranging up to 35.4 and 7.9%, respectively, at a biochar application rate of 8%. Similarly, biochar induced increments in exchangeable Ca2+ up to 38.6% and declines up to 11.4%, at an 8% biochar application rate. The increment in CEC and exchangeable Ca2+ content was found in soils with lower starting exchangeable Ca2+ contents than the biochar added, while decreases were observed in soils with higher exchangeable Ca2+ contents than the biochar. The original pH, CEC, exchangeable Ca2+, and texture of the soils represented the most crucial factors for determining the amount of change in soil pH, CEC, and exchangeable Ca2+ content.ConclusionsOur findings clearly demonstrate that application of a uniform biochar to a range of soils under equivalent environmental conditions induced two contradicting effects on soil properties including soil CEC and exchangeable Ca2+ content. Therefore, knowledge of both biochar and soil properties will substantially improve prediction of biochar application efficiency to improve soil properties. Among important soil properties, soil exchangeable Ca2+ content is the primary factor controlling the direction of biochar-induced change in soil CEC and exchangeable Ca2+ content. Generally, biochar can induce changes in soil pH, CEC, and exchangeable Ca2+, K+, and Mg2+ with the effectiveness and magnitude of change closely related to the soil’s original properties.

Synthetic dyes are common water contaminants that impair water quality and cause diseases such as dermatitis, cancer and dysfunction of kidneys. There is therefore a need for adsorbent materials to remove dyes from water. Here a bentonite/zeolite-NaP composite was synthesized by alkaline treatment of bentonite at 150 °C for 4 h. The composite exhibits nearly cubic zeolite-NaP crystals dispersed throughout bentonite aggregates. This composite has 512 m2/g surface area, 387 meq/100 g cation exchange capacity and 5.4 nm average pore diameter. The composite shows high removal efficiency for methylene blue, of 94%, and Congo red, of 93%, after 720 min at an initial concentration of 5 mg/l.

Solid organic matter (OM) is a biogeochemically relevant constituent of soils and sediments. It also affects sediments' geophysical properties, but is often overlooked in hydro‐ and biogeophysical approaches for the characterization of the shallow subsurface. Here, we explore the potential of spectral induced polarization (SIP) to delineate OM‐rich zones in the subsurface and provide insights into the mechanisms that drive OM‐polarization using measurements on both field cores and artificial OM‐sand mixtures. Both, field samples and artificial mixtures showed a linear relationship between the total organic carbon (TOC) content and charge storage (imaginary conductivity). The high cation exchange capacity of OM drives the increase in polarization and can help in delineating potentially microbially active OM‐rich zones in cores or field surveys. To avoid misinterpretation of SIP data in unconsolidated media, we strongly suggest quantifying TOC content in sediment samples to accompany the interpretation of field surveys. Plain Language Summary Soils and sediments are mixtures of minerals, water, air and partly decomposed organic matter (OM) derived from plants and soil organisms. The field of geophysics measures the electrical, seismic, and magnetic properties of soils and sediments and relates them to the minerals to derive images of their composition. The contribution of the organic fraction is largely ignored. We performed experiments that show that the organic‐matter fraction can contribute significantly to the electrical signal of sediments. In fact, our data show that we can locate areas of high organic content in soils using the geophysical technique of spectral induced polarization. We performed measurement on sediment profiles from a natural aquifer and lab experiments on mixtures of peat and sand, to derive a relationship between organic content and the charge storage capacity of sediments. Our results show the potential of using geophysics to map out organic content in sediments, and caution the disregard for OM when deriving physical models of sediment using electrical measurements. Key Points Organic matter (OM) with a high cation exchange capacity can dominate the imaginary conductivity response of sediments Neglecting OM may bias petro‐physical interpretations of spectral induced polarization measurements

Stomata are simultaneously tasked with permitting the uptake of carbon dioxide for photosynthesis while limiting water loss from the plant. This process is mainly regulated by guard cell control of the stomatal aperture, but recent advancements have highlighted the importance of several genes that control stomatal development. Using targeted genetic manipulations of the stomatal lineage and a combination of gas exchange and microscopy techniques, we show that changes in stomatal development of the epidermal layer lead to coupled changes in the underlying mesophyll tissues. This coordinated response tends to match leaf photosynthetic potential (V cmax) with gas-exchange capacity (g smax), and hence the uptake of carbon dioxide for water lost. We found that different genetic regulators systematically altered tissue coordination in separate ways: the transcription factor SPEECHLESS (SPCH) primarily affected leaf size and thickness, whereas peptides in the EPIDERMAL PATTERNING FACTOR (EPF) family altered cell density in the mesophyll. It was also determined that interlayer coordination required the cellsurface receptor TOO MANY MOUTHS (TMM). These results demonstrate that stomata-specific regulators can alter mesophyll properties, which provides insight into how molecular pathways can organize leaf tissues to coordinate gas exchange and suggests new strategies for improving plant water-use efficiency.

Key messageUrban trees are passively subject to and actively mitigate urban environmental pressures. Suitable selection of tree species and appropriate management can make cities useful habitats for trees.The urban environment is stressful not only because of pollution but also due to heat and drought, creating arid conditions. Trees are passively subject to the microclimate but are also actively modifying it, and they perform important urban ecosystem services. Trees function as bio-indicators of urban conditions by morphological features and by dendrochronology and dendrobiochemistry. Anchorage and mechanical stability need to be surveyed. Among the stresses in addition to deposition of metals, there is gaseous pollution of the atmosphere (SO2, NO2, and O3). Reacting to that are leaf anatomy as well as even the fine-tuning of biochemical pathways, e.g., terpene synthesis. The significant urban stresses are heat and drought. They increase top dieback and lead to a decrease of life crown-top heights from the ground (LCTH), where water relations remain similar in the crowns at various heights. Statistics of dendrochronology allow identification of pointer years with exceptionally wide and narrow tree rings. The prevalence of pointer years helps the selection of species suited for plantation in cities. Measurements of water potential at the turgor-loss point, πtlp, indicative of the permanent wilting point also helped identifying whole-plant drought tolerance. Infection by wood-decay fungi is a hazardous urban problem, as wood-decay builds up over many years increasing the danger of tree fall. Ectomycorrhiza is hampered in urban soils having a low inoculum potential due to chemical and physical soil qualities regarding cation-exchange capacity, permanent wilting point, and availability of water. Management should be based on scientific investigations. Allometry modeling allows for quantifying ecosystem services. Surveying stability is possible for instance by noninvasive acoustic tomography. Practices are irrigation and mulching. With appropriate management, cities can be useful habitats for trees contributing to biological richness and the comfort of life in cities.

Coal gasification fine slag (CGFS), which is the by-product of entrained-flow coal gasification, has superior properties, such as a large surface area, a broad pore size distribution, and a high content of carbon. This material has the potential to amend poor soils. This study was carried out to investigate the use of CGFS as a soil amendment for alkaline sandy lands. Special focus was given to the mechanisms by which CGFS changes the physicochemical properties of soil. Characterization tests and chemical composition results further attested that the large amounts of residual carbon, fluffy structure, high surface area, and wide pore diameter of CGFS are key factors that enhance the soil physicochemical properties. When 20% CGFS was applied, the bulk density of the soil decreased from 1.47 to 1.05 g/cm3, the carbon content increased significantly from 4.86 to 55.38 g/kg, the pH decreased from 8.49 to 8.23, the cation exchange capacity (CEC) increased from 2.17 to 4.68 cmol/kg, and the water holding capacity (WHC) increased from 29 to 44%. Potted plant experiments in a greenhouse showed that 20%wt. incorporation of CGFS significantly increased the germination rates of maize and wheat from 0 to 100%. Pearson correlation analysis results indicated that the changes in the soil physicochemical properties were significantly correlated with each other (p < 0.05 or 0.01) and that the WHC was significantly correlated with the germination rates of the crops. This work demonstrated that judicious application of CGFS as a natural soil amendment could not only enhance the soil physicochemical properties but also provide a new approach for the safe and environmentally friendly utilization of CGFS.

Abstract Background Linear relationships are commonly observed between shoot magnesium ([Mg]shoot) and shoot calcium ([Ca]shoot) concentrations among angiosperm species growing in the same environment. Scope and Conclusions This article argues that, in plants that do not exhibit ‘luxury’ accumulation of Mg or Ca, (1) distinct stoichiometric relationships between [Mg]shoot and [Ca]shoot are exhibited by at least three groups of angiosperm species, namely commelinid monocots, eudicots excluding Caryophyllales, and Caryophyllales species; (2) these relationships are determined by cell wall chemistry and the Mg/Ca mass quotients in their cell walls; (3) differences between species in [Mg]shoot and [Ca]shoot within each group are associated with differences in the cation exchange capacity (CEC) of the cell walls of different species; and (4) Caryophyllales constitutively accumulate more Mg in their vacuoles than other angiosperm species when grown without a supra-sufficient Mg supply.