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Soil biota accounts for ~25% of global biodiversity and is vital to nutrient cycling and primary production. There is growing momentum to study total belowground biodiversity across large ecological scales to understand how habitat and soil properties shape belowground communities. Microbial and animal components of belowground communities follow divergent responses to soil properties and land use intensification; however, it is unclear whether this extends across heterogeneous ecosystems. Here, a national-scale metabarcoding analysis of 436 locations across 7 different temperate ecosystems shows that belowground animal and microbial (bacteria, archaea, fungi, and protists) richness follow divergent trends, whereas β-diversity does not. Animal richness is governed by intensive land use and unaffected by soil properties, while microbial richness was driven by environmental properties across land uses. Our findings demonstrate that established divergent patterns of belowground microbial and animal diversity are consistent across heterogeneous land uses and are detectable using a standardised metabarcoding approach. It is unclear whether microbes and animals residing in soils follow similar distribution patterns. Here, the authors report richness and diversity of soil microbes and invertebrates across soil, vegetation, and land use gradients in Wales, showing that land use affects animals while soil traits affect microbes.

The unknown consequences and potential impacts of mankind's ability to destroy, alter, or manipulate ecosystems on a vast scale drives our need to better understand the earth system. A fundamental challenge for soil science in the 21st century is to understand the role of soil processes in relation to the function of the earth system. The rationale for developing a definition of soil natural capital stems from the premise that we value ‘things’ based on their perceived value to human well-being. As a consequence, ignorance of the value of a resource, or system, may lead to its neglect and omission from decision making. Therefore, there is a need to develop a definition of soil natural capital, fitting within a broad framework, which can be used to assess soil ecosystem services that contribute to the function of the earth system. Though various definitions of soil natural capital have been proposed, mostly in the agricultural context, it still remains a nebulous and ill-defined term. The objective of this paper is to develop an embracing definition of soil ‘natural capital’ focusing on (i) mass, (ii) energy, and (iii) organization/entropy. Mass is further subdivided into solid, liquid and gas phases, and organization into physicochemical, biotic, and spatiotemporal structure. We differentiate between two aspects of capital, the quantity and the quality. As a result of our definition, soil moisture, temperature, and structure emerge as valuable stocks, alongside the more traditionally viewed stocks such as inorganic (mineralogy, texture) and organic materials (OM content). We go on to demonstrate how natural capital fits within the ecosystem services framework, and how using integrated valuation and process based models it can be evaluated. Finally we discuss measurement and monitoring needs that fit with this vision of evaluation.

Soil texture and the soil water characteristic are key properties used to estimate flow and transport parameters. Determination of clay content is therefore critical for understanding of plot-scale soil heterogeneity. With increasing interest in proximal soil sensing, there is the need to relate obtained signals to soil properties of interest. Inference of soil texture, especially clay mineral content, from instrument response from electromagnetic induction and radiometric methods is of substantial interest. However, the cost of soil sampling and analysis required to link proximal measurements and soil properties, for example, clay mineral content, can sometimes outweigh the benefits of using a fast proximal technique. In this paper, we propose that determination of a soil’s hygroscopic water content at 50% atmospheric relative humidity (RH50), which is time and cost efficient, and particularly suitable for developing countries, can act as a useful surrogate for clay content in interpreting soil spatial patterns based on proximal signals. We used standard clays such as kaolinite, illite, and montmorillonite to determine the water release characteristic as a function of hygroscopic water content. We also determined clay content of soils from temperate (Arizona, United States) and tropical (Trinidad) regions using the hydrometer method and hygroscopic water content for soils equilibrated at RH50. We found linear dependence of clay percentage and RH50 for a range of soil mineralogies. Hygroscopic water measurements offer an inexpensive and simple way to estimate site-specific clay mineral content that in turn can be used to interpret geophysical signal data in reconnaissance surveys.

Soil organic carbon (SOC) is a soil health indicator and understanding dynamics changing SOC stocks will help achieving net zero goals. Here we present four datasets featuring 11,750 data points covering co-located aboveground and below-ground metrics for exploring ecosystem SOC dynamics. Five sites across England with an established land use contrast, grassland and woodland next to each other, were rigorously sampled for aboveground (n = 109), surface (n = 33 soil water release curves), topsoil, and subsoil metrics. Commonly measured soil metrics were analysed in five soil increments for 0–1 metre (n = 4550). Less commonly measured soil metrics which were assumed to change across the soil profile were measured on a subset of samples only (n = 3762). Additionally, we developed a simple method for soil organic matter fractionation using density fractionation which is part of the less common metrics. Finally, soil metrics which may impact SOC dynamics, but with less confidence as to their importance across the soil profile were only measured on topsoil (~5–15 cm = mineral soil) and subsoil (below 50 cm) samples (n = 2567).

Greenhouse gas stabilisation in the atmosphere is one of the most pressing challenges of this century. Sequestering carbon in the soil by changing land use and management is increasingly proposed as part of climate mitigation strategies, but our understanding of this is limited in quantitative terms. Here we collate a substantial national and regional data set (15 790 soil cores) and analyse it in an advanced statistical modelling framework. This produced new estimates of the effects of land use on soil carbon stock (Sc) in the UK, different in magnitude and ranking order from the previous best estimates. Soil carbon stocks were highest in woodlands, followed by rough grazing, semi-natural grasslands, and improved grasslands, and they were lowest in croplands. Estimates were smaller than the previous estimates, partly because of new data, but mainly because the effect is more reliably characterised using a logarithmic transformation of the data. With the very large data set analysed here, the uncertainty in the differences among land uses was small enough to identify consistent mean effects. However, the variability in these effects was large, and this variability was similar across all surveys. This has important implications for agri-environment schemes seeking to sequester carbon in the soil by altering land use, because the effect of a given intervention is very hard to verify. We examined the validity of the “space-for-time” substitution, and, although the results were not unequivocal, we estimated that the effects are likely to be overestimated by 5 %–33 %, depending upon land use.

Ecosystems may exhibit alternative stable states (ASS) in response to environmental change. Modelling and observational data broadly support the theory of ASS, however evidence from manipulation experiments supporting this theory is limited. Here, we provide long-term manipulation and observation data supporting the existence of drought induced alternative stable soil moisture states (irreversible soil wetting) in upland Atlantic heath, dominated by Calluna vulgaris (L.) Hull. Manipulated repeated moderate summer drought and intense natural summer drought both lowered resilience resulting in shifts in soil moisture dynamics. The repeated moderate summer drought decreased winter soil moisture retention by ~10%. However, intense summer drought, superimposed on the experiment, that began in 2003 and peaked in 2005 caused an unexpected erosion of resilience and a shift to an ASS; both for the experimental drought manipulation and control plots, impairing the soil from rewetting in winter. Measurements outside plots, with vegetation removal, showed no evidence of moisture shifts. Further independent evidence supports our findings from historical soil moisture monitoring at a long-term upland hydrological observatory. The results herald the need for a new paradigm regarding our understanding of soil structure, hydraulics and climate interaction.

Encroachment of pinyon–juniper woodland into rangeland ecosystems is prevalent across the western United States. Mechanisms associated with this successful encroachment are speculative, but probably, in part, involve the effective use of water resources. We explored the ecohydrological characteristics of a two-needle pinyon pine (Pinus edulis Engelm.)–Utah juniper [Juniperus osteosperma (Torr.) Little] woodland on the Colorado Plateau in Utah. We have discovered that a high level of natural soil water repellency or hydrophobicity exists under the canopies of both pinyon and juniper species. We found, following summer precipitation events, that soil water repellency under trees concentrated the soil water below the surface through finger flow or bypass infiltration, contrasting with piston flow and much more uniform soil wetting in intercanopy locations. We propose that the trees \"engineer\" their environment, creating water repellency as a way of providing an ecohydrological advantage and reducing potential water uptake by shallow-rooted herbaceous species. In addition, we speculate that soil water repellency may be a major contributing factor to the \"nutrient islands\" observed to persist under juniper canopies even after the trees have been cut down and removed.

The Glastir Monitoring and Evaluation Programme (GMEP) ran from 2013 until 2016 and was probably the most comprehensive programme of ecological study ever undertaken at a national scale in Wales. The programme aimed to (1) set up an evaluation of the environmental effects of the Glastir agri-environment scheme and (2) quantify environmental status and trends across the wider countryside of Wales. The focus was on outcomes for climate change mitigation, biodiversity, soil and water quality, woodland expansion, and cultural landscapes. As such, GMEP included a large field-survey component, collecting data on a range of elements including vegetation, land cover and use, soils, freshwaters, birds, and insect pollinators from up to three-hundred 1 km survey squares throughout Wales. The field survey capitalised upon the UK Centre for Ecology & Hydrology (UKCEH) Countryside Survey of Great Britain, which has provided an extensive set of repeated, standardised ecological measurements since 1978. The design of both GMEP and the UKCEH Countryside Survey involved stratified-random sampling of squares from a 1 km grid, ensuring proportional representation from land classes with distinct climate, geology and physical geography. Data were collected from different land cover types and landscape features by trained professional surveyors, following standardised and published protocols. Thus, GMEP was designed so that surveys could be repeated at regular intervals to monitor the Welsh environment, including the impacts of agri-environment interventions. One such repeat survey is scheduled for 2021 under the Environment and Rural Affairs Monitoring & Modelling Programme (ERAMMP). Data from GMEP have been used to address many applied policy questions, but there is major potential for further analyses. The precise locations of data collection are not publicly available, largely for reasons of landowner confidentiality. However, the wide variety of available datasets can be (1) analysed at coarse spatial resolutions and (2) linked to each other based on square-level and plot-level identifiers, allowing exploration of relationships, trade-offs and synergies. This paper describes the key sets of raw data arising from the field survey at co-located sites (2013 to 2016). Data from each of these survey elements are available with the following digital object identifiers (DOIs): Landscape features (Maskell et al., 2020a–c), https://doi.org/10.5285/82c63533-529e-47b9-8e78-51b27028cc7f, https://doi.org/10.5285/9f8d9cc6-b552-4c8b-af09-e92743cdd3de, https://doi.org/10.5285/f481c6bf-5774-4df8-8776-c4d7bf059d40; Vegetation plots (Smart et al., 2020), https://doi.org/10.5285/71d3619c-4439-4c9e-84dc-3ca873d7f5cc; Topsoil physico-chemical properties (Robinson et al., 2019), https://doi.org/10.5285/0fa51dc6-1537-4ad6-9d06-e476c137ed09; Topsoil meso-fauna (Keith et al., 2019), https://doi.org/10.5285/1c5cf317-2f03-4fef-b060-9eccbb4d9c21; Topsoil particle size distribution (Lebron et al., 2020), https://doi.org/10.5285/d6c3cc3c-a7b7-48b2-9e61-d07454639656; Headwater stream quality metrics (Scarlett et al., 2020a), https://doi.org/10.5285/e305fa80-3d38-4576-beef-f6546fad5d45; Pond quality metrics (Scarlett et al., 2020b), https://doi.org/10.5285/687b38d3-2278-41a0-9317-2c7595d6b882; Insect pollinator and flower data (Botham et al., 2020), https://doi.org/10.5285/3c8f4e46-bf6c-4ea1-9340-571fede26ee8; and Bird counts (Siriwardena et al., 2020), https://doi.org/10.5285/31da0a94-62be-47b3-b76e-4bdef3037360.

Projected climate warming may substantially increase carbon emissions from wet organic soils, contributing to a positive feedback between the terrestrial carbon cycle and climate change. Evidence suggests that in these soils the stimulation of soil respiration by warming can be sustained over long periods of time due to the large availability of C substrates. However, the long-term response of wet organic soils to drought remains uncertain. Organo-mineral soils might be particularly vulnerable, because of their limited soil moisture pool to buffer drought events. Using a whole-ecosystem climate-change experiment in North Wales (UK) we show that soil respiration in podzolic (organo-mineral) soils from wet shrublands is more vulnerable to recurrent drought than to warming, and that the drought impact does not attenuate at decadal time scales. Stimulation of soil respiration by drought was linked to major changes in soil structure that led to a 54 % reduction in water holding capacity compared to control. Bryophyte abundance was found to buffer soil moisture losses, moderating soil CO₂efflux under warming. As there was no evidence of change in plant productivity to offset the increased soil C emissions under drought, this response may result in a positive climate feedback. The results indicate the potentially critical role that changes in sub-dominant vegetation and in soil physical properties may have in determining climate change impacts on soil C dynamics.

The observation of low dielectric values <2, consistent with the bright areas of the surface of Mars, is completely counter to expectation for soils dominated by mafic minerals, especially Fe minerals and pyroxenes that tend to have dielectric values two to three times higher than quartz, which has a value of 4.7. To this day, this observation has not been explained. The recent success of the Phoenix lander in locating water on Mars, however, is renewing interest in the use of sensors to determine Martian soil properties. We took measurements on the Hawaiian JSC Mars-1 soil simulant, considered to reflect the properties of the soils of the bright regions of Mars. Our objective was to determine if soil structure and dielectric phase configuration could account for low dielectric responses. We discovered that low dielectric values can be reconciled with mafic, Fe-bearing silicate mineralogy due to the presence of a palagonite structure with internal porosity. Furthermore, dielectric response as a function of water content is startlingly lower than standard soil calibration equations from Earth, meaning that the application of these equations may significantly underestimate water content determined from dielectric measurements—not because of “bound water,” but because of the altered dielectric phase configuration due to the palagonite internal pore structure. The implications of this finding for future planetary missions are that all sensors relying on interpreting soil properties from measurements of bulk soil electrical, thermal, or dielectric properties will be similarly affected in the presence of materials with internal porosity.