Soil textural heterogeneity impacts bacterial but not fungal diversity

Soils harbour high levels of microbial diversity, underpinning their ability to provide key soil functions and ecosystem services. The extreme variety of soil microbial life is often explained by reference to the physical and chemical heterogeneity of the soil environment. However, detailed understanding of this link is still lacking, particularly as micro-scale studies are difficult to scale up to the soil profile or landscape level. To address this, we used soil samples collected from a wide range of temperate oceanic habitats (e.g. arable, grassland, coniferous and deciduous woodland, heathland; 335 sites in total) to evaluate the link between soil texture and microbial diversity. Soil particle size distribution was measured in each sample using laser granulometry (i.e. sand, silt, clay), while the diversity of bacterial and fungal communities were determined by metabarcoding with an Illumina MiSeq using16S and ITS1 taxonomy marker gene regions, respectively. Multifractal analysis of the soil particle size distribution was then used to describe the heterogeneity of the soil particle sizes. Overall, our results showed no impact of habitat type upon textural heterogeneity indicating that it is an aspect of soil quality resistant to management decisions. Using a structural equation modelling approach, we show that soil textural heterogeneity positively influences bacterial diversity but had little impact upon fungal diversity. We also find that textural composition impacts both bacterial and fungal composition, with many specific microbial taxa showing co-occurrence relationships with clay and fine-silt sized particles. Our results strongly indicate that soil textural heterogeneity influences microbial community diversity regardless of soil management practices and biophysical activities. The close linkages between different groups of soil organisms can obscure the mechanisms driving the development of biodiversity, however, it is clear that the soil physical environment has differential impacts on organisms with different life history strategies

Decoupled richness of generalist anaerobes and sulphate-reducing bacteria is driven bypHacross land uses in temperate soils

Sulphate‐reducing bacteria (SRB) represent a key biological component of the global sulphur (S) cycle and are common in soils, where they reduce SO42− to H2S during the anaerobic degradation of soil organic matter. The factors that regulate their distribution in soil, however, remain poorly understood. We sought to determine the ecological patterns of SRB richness within a nationwide 16S metabarcoding dataset. Across 436 sites belonging to seven contrasting temperate land uses (e.g., arable, grasslands, woodlands, heathland and bog), SRB richness was relatively low across land uses but greatest in grasslands and lowest in woodlands and peat‐rich soils. There was a shift in dominant SRB taxa from Desulfosporosinus and Desulfobulbus in arable and grassland land uses to Desulfobacca in heathland and bog sites. In contrast, richness of other generalist anaerobic bacterial taxa found in our dataset (e.g., Clostridium, Geobacter and Pelobacter) followed a known trend of declining richness linked to land‐use productivity. Overall, the richness of SRBs and anaerobes had strong positive correlations with pH and sulphate concentration and strong negative relationships with elevation, soil organic matter, total carbon and carbon‐to‐nitrogen ratio. It is likely that these results reflect the driving influence of pH and competition for optimal electron acceptors with generalist anaerobic bacteria on SRB richness

Evaluation of mesofauna communities as soil quality indicators in a national-level monitoring programme

Mesofauna underpin many ecosystem functions in soils. However, mesofauna communities are often overlooked when discussing these functions on large scales. They have been proposed as bioindicators of soil quality and ecosystem health. This study aimed to evaluate differences amongst mesofauna communities, particularly Acari and Collembola, across multiple habitat and soil types, as well as organic matter levels, and their relationships with soil characteristics, on a national-scale. Soil cores were collected from 685 locations as part of a nationwide soil monitoring programme of Wales. Plant community composition, soil type, as well as physical and chemical variables, including pH, total C and N, were measured at these locations. Mesofauna were extracted from soil cores and identified using a Tullgren funnel technique. Acari were sorted to Order; Collembola were sorted according to Super-family. Abundances of mesofauna were consistently lowest in arable sites and highest in lowland woodlands, except for Mesostigmata. Differences between similar habitat types (e.g. Fertile and Infertile grasslands) were not detected using the national-level dataset and differences in mesofauna communities amongst soil types were unclear. Relationships between mesofauna groups and soil organic matter class, however, were much more informative. Oribatid abundances were lowest in mineral soils and correlated with all soil properties except moisture content. Collembola and Mesostigmata abundances were likely negatively influenced by increased moisture levels in upland peat habitats where their abundances were lowest. These groups also had low abundances in heathlands and this was reflected in low diversity values. Together, these findings show that this national-level soil survey can effectively identify differences in mesofauna community structure and correlations with soil properties. Identification of mesofauna at high taxonomic levels in national-level soil monitoring is encouraged to better understand the ecological context of changes in soil properties

Plant and soil communities are associated with the response of soil water repellency to environmental stress

A warming climate and expected changes in average and extreme rainfall emphasise the importance of understanding how the land surface routes and stores surface water. The availability and movement of water within an ecosystem is a fundamental control on biological and geophysical activity, and influences many climatic feedbacks. A key phenomenon influencing water infiltration into the land surface is soil hydrophobicity, or water repellency. Despite repellency dictating the speed, volume and pattern of water infiltration, there is still major uncertainty over whether this critical hydrological process is biologically or physicochemically controlled. Here we show that soil water repellency is likely driven by changes in the plant and soil microbial communities in response to environmental stressors. We carried out a field survey in the summers of 2013 to 2016 in a variety of temperate habitats ranging across arable, grassland, forest and bog sites. We found that moderate to extreme repellency occurs in 68% of soils at a national scale in temperate ecosystems, with 92% showing some repellency. Taking a systems approach, we show that a wetter climate and low nutrient availability alter plant, bacterial and fungal community structure, which in turn are associated with increased soil water repellency across a large-scale gradient of soil, vegetation and land-use. The stress tolerance of the plant community and associated changes in soil microbial communities were more closely linked to changes in repellency than soil physicochemical properties. Our results indicate that there are consistent responses to diverse ecosystem stresses that will impact plant and microbial community composition, soil properties, and hydrological behaviour. We suggest that the ability of a biological community to induce such hydrological responses will influence the resilience of the whole ecosystem to environmental stress. This highlights the crucial role of above-belowground interactions in mediating climatic feedbacks and dictating ecosystem health

Global environmental changes impact soil hydraulic functions through biophysical feedbacks

Although only representing 0.05% of global freshwater, or 0.001% of all global water, soil water supports all terrestrial biological life. Soil moisture behaviour in most models is constrained by hydraulic parameters that do not change. Here we argue that biological feedbacks from plants, macro‐fauna and the microbiome influence soil structure, and thus the soil hydraulic parameters and the soil water content signals we observe. Incorporating biological feedbacks into soil hydrological models is therefore important for understanding environmental change and its impacts on ecosystems. We anticipate that environmental change will accelerate and modify soil hydraulic function. Increasingly we understand the vital role that soil moisture exerts on the carbon cycle and other environmental threats such as heatwaves, droughts and floods, wildfires, regional precipitation patterns, disease regulation and infrastructure stability, in addition to agricultural production. Biological feedbacks may result in changes to soil hydraulic function that could be irreversible, resulting in alternative stable states (ASS) of soil moisture. To explore this, we need models that consider all the major feedbacks between soil properties and soil‐plant‐faunal‐microbial‐atmospheric processes, which is something we currently do not have. Therefore, a new direction is required to incorporate a dynamic description of soil structure and hydraulic property evolution into soil‐plant‐atmosphere, or land surface, models that consider feedbacks from land use and climate drivers of change, so as to better model ecosystem dynamics

Experimental evidence for drought induced alternative stable states of soil moisture

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

The effects of land use on soil carbon stocks in the UK

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 (15790 soil cores), and analyse it in an advanced statistical modelling framework. This produced new estimates of the effects of land use on soil carbon stocks 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 and semi-natural grasslands, then improved grasslands, and 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 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 over-estimated by 5–33 %, depending upon land use

Final report on project SP1210: Lowland peatland systems in England and Wales – evaluating greenhouse gas fluxes and carbon balances

Lowland peatlands represent one of the most carbon-rich ecosystems in the UK. As a result of widespread habitat modification and drainage to support agriculture and peat extraction, they have been converted from natural carbon sinks into major carbon sources, and are now amongst the largest sources of greenhouse gas (GHG) emissions from the UK land-use sector. Despite this, they have previously received relatively little policy attention, and measures to reduce GHG emissions either through re-wetting and restoration or improved management of agricultural land remain at a relatively early stage. In part, this has stemmed from a lack of reliable measurements on the carbon and GHG balance of UK lowland peatlands. This project aimed to address this evidence gap via an unprecedented programme of consistent, multi year field measurements at a total of 15 lowland peatland sites in England and Wales, ranging from conservation managed ‘near-natural’ ecosystems to intensively managed agricultural and extraction sites. The use of standardised measurement and data analysis protocols allowed the magnitude of GHG emissions and removals by peatlands to be quantified across this heterogeneous data set, and for controlling factors to be identified. The network of seven flux towers established during the project is believed to be unique on peatlands globally, and has provided new insights into the processes the control GHG fluxes in lowland peatlands. The work undertaken is intended to support the future development and implementation of agricultural management and restoration measures aimed at reducing the contribution of these important ecosystems to UK GHG emissions

Fifty years of reduction in sulphur deposition drives recovery in soil pH and plant communities

1. Sulphur deposition through rainfall has led to species loss and ecosystem degradation globally, and across Europe huge reductions in sulphur emissions since the 1970s were expected to promote the recovery of acidified ecosystems. However, the rate and ecological impact of recovery from acidification in terrestrial ecosystems is still unclear as is the influence of management and climate, as to date there has been no long-term spatially extensive evaluation of these changes. 2. Here, we present data from thousands of sites across Great Britain (pH range 3.3–8.7) surveyed repeatedly from 1978–2019 and assess change in soil pH and plant acidity preference (Ellenberg R) in response to atmospheric deposition of sulphur and nitrogen. We analyse change in grasslands managed for pasture, referred to as high-intensity habitats, and compare to seminatural habitats comprising rough grassland, broadleaved woodland, bog and heathland, referred to as low-intensity habitats. 3. Soil pH increased from 1978 to 2007 but then decreased between 2007 and 2019, resulting in a net increase of ~0.2 pH units in low-intensity habitats but no change in high-intensity habitats. The community average Ellenberg R increased in seminatural habitats by ~0.2 units but remained stable in intensive grasslands. 4. In seminatural habitats, but not intensive grasslands, these changes in plant community composition were associated with the soil pH changes which were in turn linked to decreasing sulphur deposition and differences in rainfall. 5. Nitrogen deposition, which was relatively stable over the survey period, showed no additional effect upon soil acidity once sulphur deposition was accounted for. 6. Synthesis: Our results provide conclusive evidence that reductions in acid emissions are stimulating the gradual recovery of chronically acidified terrestrial ecosystems at a whole-country scale, while also suggesting this recovery is being compromised by changing climate and land management

Divergent national-scale trends of microbial and animal biodiversity revealed across diverse temperate soil ecosystems

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