Extensive green roofs can mitigate the adverse effects of urban nature loss by providing ecosystem services, such as biodiversity increase, stormwater management and temperature regulation. They also sequester carbon, retain nutrients and potentially improve urban air and rainwater quality. This study examined how roof age, substrate depth, fertilization and vegetation type affect carbon, nitrogen and phosphorus substrate stocks, as well as two nitrogen fluxes (mineralization and nitrification). We hypothesized that vegetation type (Sedum-only vs. diverse vegetation), substrate depth and fertilization would be the main drivers of these stocks and fluxes. Twelve extensive green roofs in three cities in Flanders, Belgium, were sampled across four seasons. Results suggest limited carbon sequestration potential. Roofs with diverse vegetation, particularly those with mosses and herbs, had higher total carbon and nitrogen substrate stocks. Carbon stocks ranged from 1400 to 2880 g m− 2 (mean: 1600 g m− 2) in diverse roofs, compared to 700–1050 g m− 2 (mean: 860 g m− 2; p < 0.001) in species-poor roofs. Nitrogen stocks ranged from 62 to 100 g m− 2 (mean: 83 g m− 2) in diverse roofs and between 38 and 60 g m− 2 (mean: 50 g m− 2; p < 0.001) in species-poor roofs. Fertilization had no significant effect, while substrate depth only influenced phosphorus substrate stocks (p = 0.012). Overall, extensive green roofs offer limited carbon sequestration and nutrient retention. However, optimizing substrate composition and increasing plant diversity could enhance these benefits. This study highlights the potential for improving green roof performance through better design and management.

Decarbonization of anthropogenic activities is critical to limit global warming. Enhanced silicate weathering (ESW) is a promising negative emission technology that permanently removes CO2 through chemical reactions between silicates and water. However, traditional ex-situ processes are often cost-prohibitive, and in-situ approaches face challenges related to monitoring, leakage risks, and slow kinetics. Recent research indicates that biota (e.g., bacteria, fungi, earthworms) can enhance weathering rates, but the synergistic potential of multiple biota types remains underexplored. This study evaluates the techno-economic potential of a novel bioreactor concept that integrates multiple biota types with silicates, water and a CO2 source to bio-accelerate CO2 sequestration under milder, lower cost conditions. A prospective techno-economic assessment was conducted for three feedstock scenarios: 1) basalt and straw, 2) diabase and biochar and 3) steel slag and biochar, using Germany as a representative industrial case. For each scenario, the maximum economically viable rock use was determined relative to the European Emission Trading System (ETS) price of 90 /tCO2, and minimum sequestration target capacities were identified. Results indicate that the steel slag and biochar scenario is the most favorable, requiring a minimum sequestration capacity of 415 kgCOQ/t rock. Sensitivity analysis highlighted the COQ sequestration capacity, rock usage, feedstock cost, and transport logistics as key cost drivers. This study addresses an identified gap in techno-economic assessments of biologically assisted weathering systems and provides development targets for future optimization. The findings suggest that biota-assisted ESW reactors could offer a viable pathway for scalable and economically competitive COQ removal.

The development of carbon dioxide removal methods, coupled with decreased CO2 emissions, is fundamental to achieving the targets outlined in the Paris Agreement limiting global warming to 1.5 °C. Here we are investigating the importance of the organic carbon feedstock to support silicate mineral weathering in small-scale flow through bioreactors and subsequent CO2 sequestration. Here, we combine two bacteria and two fungi, widely reported for their weathering potential, in simple flow through bioreactors (columns) consisting of forsterite and widely available, cheap organic carbon sources (wheat straw, bio-waste digestate of pig manure and biowaste, and manure compost), over six weeks. Compared to their corresponding abiotic controls, the inoculated straw and digestate columns release more total alkalinity (~2 times more) and produce greater dissolved and solid inorganic carbon (29% for straw and 13% for digestate), suggesting an increase in CO2 sequestration because of bio-enhanced silicate weathering. Microbial biomass is higher in the straw columns compared to the digestate and manure compost columns, with a phospholipid fatty acid derived total microbial biomass 10 x greater than the other biotic columns. Scanning Electron Microscopy imaging shows the most extensive colonisation and biofilm formation on the mineral surfaces in the straw columns. The biotic straw and digestate columns sequester 50 and 14 mg C more than their abiotic controls respectively, while there is no difference in the manure columns. The selection of organic carbon sources to support microbial communities in the flow through bioreactors controlls the silicate weathering rates and CO2 sequestration.

Anthropogenic land use alters soil properties and influences biological transformations in the root zone, thereby affecting the distribution and supply of soil nutrients. It is generally acknowledged that human land-use activities such as intensive cattle farming and cultivation of citrus products lead to a homogenization of soil nutrients. This research aims at investigating the heterogeneity in soil nutrient stocks and BSi stocks (a beneficial plant element) within the Savannah biome of South Africa. In this study, C-N-Si stocks and their ratios were quantified in the soil of five different land use types, common in South Africa. The five different land use types are i) bush savannahs, ii) mopane-dominated woodlands, iii) annually burned land, iv) communal grazing land and v) citrus orchards. Empirical research however could not fully validate this hypothesis. In particular fire management and game farming (natural land use type) led to more variability in nutrient pools, with occasional occurrences of C-N-Si hotspots. Our results suggest that when ecosystem analysis of soil nutrient and carbon stocks is handled as a homogeneous unit potentially large mistakes are made, even in anthropogenic landscapes previously hypothesized with uniform nutrient distributions.

Enhanced weathering (EW) is an emerging carbon dioxide (CO2) removal technology that can contribute to climate change mitigation. This technology relies on accelerating the natural process of mineral weathering in soils by manipulating the abiotic variables that govern this process, in particular mineral grain size and exposure to acids dissolved in water. EW mainly aims at reducing atmospheric CO2 concentrations by enhancing inorganic carbon sequestration. Until now, knowledge of EW has been mainly gained through experiments that focused on the abiotic variables known for stimulating mineral weathering, thereby neglecting the potential influence of biotic components. While bacteria, fungi, and earthworms are known to increase mineral weathering rates, the use of soil organisms in the context of EW remains underexplored. This protocol describes the design and construction of an experimental setup developed to enhance mineral weathering rates through soil organisms while concurrently controlling abiotic conditions. The setup is designed to maximize weathering rates while maintaining soil organisms' activity. It consists of a large number of columns filled with rock powder and organic material, located in a climate chamber and with water applied via a downflow irrigation system. Columns are placed above a fridge containing jerrycans to collect the leachate. Representative results demonstrate that this setup is suitable to ensure the activity of soil organisms and quantify their effect on inorganic carbon sequestration. Challenges remain in minimizing leachate losses, ensuring homogeneous ventilation through the climate chamber, and avoiding flooding of the columns. With this setup, an innovative and promising approach is proposed to enhance mineral weathering rates through the activity of soil biota and disentangle the effect of biotic and abiotic factors as drivers of EW.

Enhanced weathering (EW) of silicate rocks is a negative emission technology that captures CO 2 from the atmosphere. Olivine (Mg 2 SiO 4 ) is a fast weathering silicate mineral that can be used for EW and is abundant in dunite rock. In addition to CO 2 sequestration, EW also has co-benefits in an agricultural context. Adding silicate minerals to soils can significantly improve crop health and growth as the weathering releases elements such as silicon (Si) that can stimulate crop growth and increase stress resistance, a co-benefit that is becoming increasingly important as global warming proceeds. However, dunite also contains heavy metals, especially nickel (Ni) and chromium (Cr), potentially limiting its use in an agricultural context. In this study, we investigate the influence of dunite addition on growth of barley and wheat in a mesocosm experiment. We amended the soil with the equivalent of 220 ton ha -1 dunite, using two grain sizes (p 80 = 1020 µm and p 80 = 43.5 µm), under two rainfall regimes (each receiving the same amount of 800 mm water y −1 but at daily versus weekly rainfall frequency). Our results indicate that the amendment of fine dunite increased leaf biomass but only with daily rainfall. Aboveground biomass was significantly reduced with weekly rainfall compared to daily rainfall, but this reduction was slightly alleviated by fine dunite application for wheat. This indicates a positive effect of dunite during drying-rewetting cycles. For barley the negative effect of reduced rainfall frequency was not counterbalanced by dunite application. Contrary to our expectations, calcium (Ca) and Si concentrations in crops decreased with fine dunite application, while, as expected, magnesium (Mg) concentration increased. Coarse dunite application did not significantly affect crop nutrient concentrations, most likely due to its lower weathering rate. In contrast to what was expected, plant Ni and Cr concentrations did not increase with dunite application. Hence, despite high dunite application in our experiment, plants did not accumulate these heavy metals, and only benefited from the released nutrients, albeit dependent on grain size and rainfall frequency.

With rising population growth, there is a need for increased food production. With rising temperatures and more frequent droughts due to climate change, it becomes more challenging to keep up with this increased demand for food. Therefore, a change in land use and management is needed in which enhanced silicate weathering (ESW) can play an important role. Weathering of silicate rocks has been regulating the atmospheric CO2 concentrations for over decades, but with the rise in atmospheric CO2, the natural weathering is too slow. Grinding the silicate rocks into a fine powder and spread it over for example agricultural fields will increase the reactive surface area and hence, the amount of CO2 that is stored in soils. The application of silicate minerals to soils can enhance plant growth by multiple processes, for example by counteracting soil acidification and by the release of plant nutrients. In this way, ESW can be used on agricultural fields without competing for land like other carbon capture techniques (e.g. Bio-Energy with carbon capture and storage). This study investigates the use of olivine (a fast-weathering Mg-rich silicate mineral) as a fertilizer in agriculture using a full-factorial mesocosm experiment. Barley and wheat were grown under two different rain regimes (daily rain vs weekly rain) and with application of two different grain sizes of olivine (p80 = 1020 µm and p80 = 43.5 µm). Our results showed increased plant growth and biomass with olivine addition, albeit only for fine olivine. However, this was not translated in an increase in yield of wheat and barley. Besides changes in biomass, we found significant differences in plant nutrient concentrations. As expected, Mg concentration increased significantly. However, BSi and Ca concentrations decreased with fine olivine application. Nitrogen in grains was also increased in the fine olivine treatment. In contrast to fine olivine, coarse olivine addition had almost no influence on nutrients. Ca, Mg and Si concentrations in plant samples followed the same trend as in the soil pore water, in contrast to metal concentrations. Olivine addition increased Ni and Cr availability in the soil pore water, but the concentrations of these elements in plant tissue did not increase and were even below detection limit for the majority of samples. While the influence of olivine on metal concentrations in plant samples was not affected by rain treatment, the influence of olivine on nutrients in the plants and plant growth was. Fine olivine addition enhanced the plants resistance to drought as it reduced the decrease in biomass with weekly rain treatment compared to daily rain treatment. This positive effect of olivine addition can be due to the increased weathering rate in combination with enhancement of soil properties like increased soil water retention. In this way, the use of olivine as a fertilizer on agricultural fields can mitigate climate change while it can also contribute to the solution for increased food demand.

Quantifying and analysing leaching water is essential to understand water and nutrient cycles and the vertical transport of elements through soils. Zero tension lysimeters (ZTLs) have been widely used to capture the soil solution leaching by gravity. This study designed and evaluated a 3D-printed ZTL (ZTL(3D)) with specific characteristics and materials to quantitatively capture dissolved element fluxes. By 3D-printing the ZTLs, we were able to include specific 3D structures and precise details in the design allowing installation of samplers from the surface rather than trenches, and thus avoiding the need for installation trenches to remain open. The ZTLs(3D) connect directly with the surface, do not depend on secondary collectors, can be installed at any depth, and samplers are easily retractable when dismantling the field set up. The material used, Nylon 12, was tested for dissolved organic carbon (DOC) release. The ZTL(3D) design was printed in two different external shapes while characteristics and internal design were identical. The difference in external shape was to study the effects of two contrasting types of installation: a cylindrical sampler for vertical installation (by soil coring from the surface) and a rectangular samplers for horizontal installation (from a pit or a trench wall). We installed them at different depths (2, 30 and 75 cm) in a forest soil and conducted rainfall simulation experiments. A water bucket model (WBM), created to calculate the water drainage fluxes that the ZTLs(3D) should collect, reproduced very well the variation in soil water content measured by soil moisture sensors installed adjacent to the ZTLs(3D) at 16, 30, 50 and 75 cm depth. Drainage fluxes simulated by the WBM showed that the vertical installation performed better at collecting water at all depths than the horizontal installation, but overall the ZTLs(3D) failed to collect the simulated amounts of drainage water. Nonetheless, the ZTLs(3D) did collect leachate water, enabling their chemical analysis. Combining the concentrations in the water collected by the ZTLs(3D) with the modelled drainage fluxes does allow estimation of DOC- and elemental leaching rates. This article presents the novel design of these two types of ZTLs(3D) because future improvements may result in better performance, and discusses their (dis)agreement with the modelled WBM fluxes. Highlights New 3D-printed zero tension lysimeters (ZTLs) to capture element fluxes when installed vertically (cylindrical design) or horizontally (cubic design) were tested. Two external sampler shapes were created to optimise the installation process and both collected drainage water successfully. Vertical installation ZTLs worked better than horizontal types, but neither well-reflected drainage fluxes simulated by water bucket model (WBM). Combined with WBM, both ZTL types provided a reliable method for quantifying nutrient and organic carbon leaching at different soil depths.

A number of negative emission technologies (NETs) have been proposed to actively remove CO2 from the atmosphere, with enhanced silicate weathering (ESW) as a relatively new NET with considerable climate change mitigation potential. Models calibrated to ESW rates in lab experiments estimate the global potential for inorganic carbon sequestration by ESW at about 0.5-5 Gt CO2 year(-1), suggesting ESW could be an important component of the future NETs mix. In real soils, however, weathering rates may differ strongly from lab conditions. Research on natural weathering has shown that biota such as plants, microbes, and macro-invertebrates can strongly affect weathering rates, but biotic effects were excluded from most ESW lab assessments. Moreover, ESW may alter soil organic carbon sequestration and greenhouse gas emissions by influencing physicochemical and biological processes, which holds the potential to perpetuate even larger negative emissions. Here, we argue that it is likely that the climate change mitigation effect of ESW will be governed by biological processes, emphasizing the need to put these processes on the agenda of this emerging research field.

Societal Impact Statement Mitigating climate change and increasing agricultural sustainability are twin challenges society faces in the upcoming decades. One measure that can contribute to reducing atmospheric CO 2 is "enhanced weathering" through application of ground silicates. Here we propose that mycorrhizal fungi may critically contribute to the success of enhanced weathering in agricultural systems. Fundamental lab‐based experiments now need to go hand in hand with real‐world field trials, with the goal to optimize both decarbonization and environmental sustainability of agricultural ecosystems. Summary Arbuscular mycorrhizal fungi have significantly contributed to weathering of the earth's surface since their evolutionary origin 400–500 million years ago. They have been a key player in the global carbon cycle over geological timescales. In order to reach the global warming targets as agreed at the Paris summit in 2015, implementation of negative emission technologies is necessary. Among the options, one of the simplest is "enhanced weathering", where silicate rock is ground into small particles to enhance weathering rate. Here we synthesize the ways by which mycorrhizal fungi interact with these particles when applied to agricultural fields, and suggest they may stimulate weathering by various direct and indirect mechanisms. We conclude that because the intensity with which mycorrhiza interact with soil is tightly related to plant provisioning of photosynthates in exchange for soil‐derived nutrients, weathering rates and hence carbon sequestration are likely to increase with agricultural activities that stimulate plant reliance on and investment in arbuscular mycorrhizal fungi.

Increasing urbanization brings along problems such as elevated CO2 emissions, eutrophication, air and water pollution, floods, rising temperature and a decrease in biodiversity. Urban green infrastructures, such as green roofs, have the potential to help mitigate those by using the properties of natural ecosystems and the services they provide in a “engineered” way. Green roofs can for example act as buffers and filters for carbon (C), nutrients, such as nitrogen (N) and phosphorus (P), and water. Hereby improving CO2 concentrations in the atmosphere by capturing it in plant biomass and improving eutrophication by retaining some dissolved organic carbon (DOC) and mineral N and P in the substrate. In this research we determine which green roof properties affect the C, N and P cycle in a beneficial way. Therefore, we investigate the influence of different parameters (i.e. roof age, roof size, vegetation type (Sedum and herbs vs. Sedum-only), fertilization, substrate depth, substrate water content, substrate bulk density, substrate pH, plant biomass, plant C/N ratio, N mineralization and nitrification) on the C and nutrient stocks of green roofs. We hypothesize that vegetation type and roof age will be the main factors influencing the C and nutrient stocks. A roof with Sedum and herbs will have a higher nutrient and C input resulting in higher stocks compared to a Sedum-only roof because herbs have a higher turn-over rate compared to Sedum-species. Furthermore, older roofs will stock more C. In the beginning C will be mainly sequestered in plant biomass until the roof is densely covered. Here after, green roofs will be able to build up an organic matter layer if the net primary production exceeds decomposition. To assess the influence of these parameters on the C, N and P stocks, twelve extensive green roofs were investigated in Belgium. The substrate and vegetation of every roof was sampled at four timepoints (spring, summer and autumn of 2019, winter 2020). Substrate samples were analyzed for stocks (total C, total N, total P) along with other abiotic soil parameters as well as some key soil processes (N mineralization and relative nitrification) for soil fertility. Our first findings show, as expected, that roofs with Sedum and herbs have an increased total C, N and P in their substrate. In addition, C and P stocks are significantly influenced by roof age: while P stocks slightly decrease over time, C stocks only increased transiently —against our predictions—, with a peak at around 9 years old.

Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, United Kingdom, 2 Institute of the Surface-Earth System Science, Tianjin University, Tianjin, China, Department of Ancient Scripture, Brigham Young University, Provo, UT, United States, 4 R.H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel, Department of Biology, Global Change Ecology Centre,

Dissolved Si (DSi) provision from land systems triggers diatom growth and CO 2 sequestration. Soils and ecosystems act as a Si “filter”, transforming DSi originated from mineral weathering into biogenic Si (BSi) after DSi uptake by plants, or into other pedogenic forms of Si (non-BSi). Land use changes the quantity of BSi and non-BSi pools along the soil profile. However, methods used to isolate Si pools include chemical extractions at high temperatures and alkaline environments and therefore are unable to provide information concerning the dissolution potential of BSi and non-BSi pools under normal conditions of temperature and pH. Here, we conducted a batch experiment where forest, pasture and cropland soil samples were mixed with water at 25 °C and pH 7. The soil samples were collected from a temperate land use gradient located in the Belgian Loess Belt. We measured dissolved Si and aluminium (Al) during 80 days. BSi and non-BSi pool contents along the soil profile were known, as they had been established previously through chemical extraction. Results show that BSi and non-BSi enriched samples present distinct Si and Al dissolution curves. While non-BSi pools contribute significantly with immediate availability of Si, BSi pools present an initial slow dissolution. Therefore, croplands that were depleted of phytoliths and had poorly organic horizons display higher concentrations of initial dissolved Si, while pastures and forests, where pedogenic pools dominate only at depths below 40 cm, have more limited initial Si release.

The weathering of silicates is a major control on atmospheric CO2 at geologic timescales. It was proposed to enhance this process to actively remove CO2 from the atmosphere. While there are some studies that propose and theoretically analyze the application of rock powder to agricultural land, results from field experiments are still scarce. In order to evaluate the efficiency and side effects of Enhanced Weathering (EW), a mesocosm experiment was set up and agricultural soil from Belgium was amended with olivine-bearing dunite ground to two different grain sizes, while distinguishing setups with and without crops. Based on measurements of Mg, Si, pH, and DIC, the additional weathering effect of olivine could be confirmed. Calculated weathering rates are up to 3 orders of magnitude lower than found in other studies. The calculated CO2 consumption by weathering based on the outlet water of the mesocosm systems was low with 2.3–4.9 tCO2km-2a-1 if compared with previous theoretical estimates. Suspected causes were the removal or dilution of Mg as a weathering product by processes like adsorption, mineralization, plant uptake, evapotranspiration, and/or preferential flow, not specifically addressed in previous EW experiments for CO2 consumption. The observation that Mg concentrations in the upper soil layers were about 1 order of magnitude higher than in the outlet water indicates that a careful tracking of weathering indicators like Mg in the field is essential for a precise estimate of the CO2 consumption potential of EW, specifically under global deployment scenarios with a high diversity of ecosystem settings. Porewater Mg∕Si molar ratios suggest that dissolved Si is reprecipitating, forming a cation-depleted Si layer on the reactive mineral surface of freshly ground rocks. The release of potentially harmful trace elements is an acknowledged side effect of EW. Primarily Ni and Cr are elevated in the soil solution, while Ni concentrations exceed the limits of drinking water quality. The use of olivine, rich in Ni and Cr, is not recommended, and alternative rock sources are suggested for the application.

While the importance of grasslands in terrestrial silicon (Si) cycling and fluxes to rivers is established, the influence of large grazers has not been considered. Here, we show that hippopotamuses are key actors in the savannah biogeochemical Si cycle. Through a detailed analysis of Si concentrations and stable isotope compositions in multiple ecosystem compartments of a savannah-river continuum, we constrain the processes influencing the Si flux. Hippos transport 0.4 metric tons of Si day-1 by foraging grass on land and directly egesting in the water. As such, they bypass complex retention processes in secondary soil Si pools. By balancing internal processes of dissolution and precipitation in the river sediment, we calculate that hippos affect up to 76% of the total Si flux. This can have a large impact on downstream lake ecosystems, where Si availability directly affects primary production in the diatom-dominated phytoplankton communities.

A social network approach provides a valuable framework to assess and strengthen teacher collaboration, which is considered important in realizing inclusive education. However, to our knowledge. there is no research that has used a social network approach to measure and strengthen teacher collaboration in the context of inclusive education. Therefore, this study aims to develop and validate a social network instrument that provides teachers, school teams and researchers insight into teacher collaboration in the light of inclusive education. Regarding the development, specific issues that need to be taken into account in developing a network questionnaire are shown and applied. Regarding the validation. evidence on the content, response processes and internal structure of the instrument are provided. Additionally, the cognitive load to complete the instrument and the value of feedback after completing the instrument are studied. Data were gathered in three primary and two secondary schools through a mixed method design, using an online questionnaire (N = 91) and focus groups and interviews with a subset of the participants (N = 23). The findings suggest that our instrument is a valid tool to assess teacher collaboration. and to strengthen teacher collaboration by providing teachers and teams feedback on their networks.