Showing papers by "Richard D. Bardgett published in 2016"

The significance of soils and soil science towards realization of the United Nations sustainable development goals

Abstract: . In this forum paper we discuss how soil scientists can help to reach the recently adopted UN Sustainable Development Goals (SDGs) in the most effective manner. Soil science, as a land-related discipline, has important links to several of the SDGs, which are demonstrated through the functions of soils and the ecosystem services that are linked to those functions (see graphical abstract in the Supplement). We explore and discuss how soil scientists can rise to the challenge both internally, in terms of our procedures and practices, and externally, in terms of our relations with colleague scientists in other disciplines, diverse groups of stakeholders and the policy arena. To meet these goals we recommend the following steps to be taken by the soil science community as a whole: (i) embrace the UN SDGs, as they provide a platform that allows soil science to demonstrate its relevance for realizing a sustainable society by 2030; (ii) show the specific value of soil science: research should explicitly show how using modern soil information can improve the results of inter- and transdisciplinary studies on SDGs related to food security, water scarcity, climate change, biodiversity loss and health threats; (iii) take leadership in overarching system analysis of ecosystems, as soils and soil scientists have an integrated nature and this places soil scientists in a unique position; (iii) raise awareness of soil organic matter as a key attribute of soils to illustrate its importance for soil functions and ecosystem services; (iv) improve the transfer of knowledge through knowledge brokers with a soil background; (v) start at the basis: educational programmes are needed at all levels, starting in primary schools, and emphasizing practical, down-to-earth examples; (vi) facilitate communication with the policy arena by framing research in terms that resonate with politicians in terms of the policy cycle or by considering drivers, pressures and responses affecting impacts of land use change; and finally (vii) all this is only possible if researchers, with soil scientists in the front lines, look over the hedge towards other disciplines, to the world at large and to the policy arena, reaching over to listen first, as a basis for genuine collaboration.

Plant diversity and root traits benefit physical properties key to soil function in grasslands

Abstract: Plant diversity loss impairs ecosystem functioning, including important effects on soil. Most studies that have explored plant diversity effects belowground, however, have largely focused on biological processes. As such, our understanding of how plant diversity impacts the soil physical environment remains limited, despite the fundamental role soil physical structure plays in ensuring soil function and ecosystem service provision. Here, in both a glasshouse and a long-term field study, we show that high plant diversity in grassland systems increases soil aggregate stability, a vital structural property of soil, and that root traits play a major role in determining diversity effects. We also reveal that the presence of particular plant species within mixed communities affects an even wider range of soil physical processes, including hydrology and soil strength regimes. Our results indicate that alongside well-documented effects on ecosystem functioning, plant diversity and root traits also benefit essential soil physical properties.

Global soil biodiversity atlas

Abstract: 2015 was the United Nations International Year of Soils and, for the first time, soils and the life within them were in the spotlight globally. An international group of experts and scientists from the European Commission’s Joint Research Centre (JRC), in close collaboration with colleagues from the Commission’s Directorate-General for the Environment and the Global Soil Biodiversity Initiative, have produced the first ever Global Soil Biodiversity Atlas. Soils are vital for human survival and underpin many sectors of our economy. It is estimated that 99% of the world’s food comes from the terrestrial environment. But soils are also home to over a quarter of global biodiversity. Millions of soil-dwelling organisms promote essential ecosystem services – from plant growth to food production. They support biodiversity, benefit human health, promote the regulation of nutrient cycles that in turn influence climate, and represent an unexplored capital of natural sources. Our knowledge of soil life is growing continuously, thanks to recent technological advances and awareness of its value. However, it is estimated that only 1% of soil microorganism species have been identified. Therefore, understanding the highly complex and dynamic life below ground remains one of the most fascinating challenges facing scientists today. A clearer picture of our soils will allow us to better understand environmental and global climate change processes whilst also exploring possible adaptation strategies. Pressures on soil organisms are well known. An ever increasing global population, and increased demand for food and fibre lead to intensified agriculture, greater use of fertilisers and pesticides as well as monocultures. Unsustainable agricultural practices, climate change, soil erosion and loss of aboveground diversity all negatively affect organisms that live in soil. To develop actions that will preserve soil life, we need to better understand the consequences of the loss of soil biodiversity. The Global Soil Biodiversity Atlas raises awareness of the role of soil organisms in sustaining life on our planet, and presents the latest research on soil biodiversity. It is also a major contribution to the EU target of halting the loss of biodiversity and ecosystem services in the EU by 2020, and the goals of the 2030 Agenda for Sustainable Development on sustainable food production and fighting land degradation. This publication marks a crucial step towards a global coordinated effort to assess life below ground, and highlights the need to improve soil conservation and the diversity of life within it.

Legacy effects of grassland management on soil carbon to depth.

Abstract: The importance of managing land to optimize carbon sequestration for climate change mitigation is widely recognized, with grasslands being identified as having the potential to sequester additional carbon. However, most soil carbon inventories only consider surface soils, and most large-scale surveys group ecosystems into broad habitats without considering management intensity. Consequently, little is known about the quantity of deep soil carbon and its sensitivity to management. From a nationwide survey of grassland soils to 1 m depth, we show that carbon in grassland soils is vulnerable to management and that these management effects can be detected to considerable depth down the soil profile, albeit at decreasing significance with depth. Carbon concentrations in soil decreased as management intensity increased, but greatest soil carbon stocks (accounting for bulk density differences), were at intermediate levels of management. Our study also highlights the considerable amounts of carbon in subsurface soil below 30 cm, which is missed by standard carbon inventories. We estimate grassland soil carbon in Great Britain to be 2097 Tg C to a depth of 1 m, with ~60% of this carbon being below 30 cm. Total stocks of soil carbon (t ha(-1) ) to 1 m depth were 10.7% greater at intermediate relative to intensive management, which equates to 10.1 t ha(-1) in surface soils (0-30 cm), and 13.7 t ha(-1) in soils from 30 to 100 cm depth. Our findings highlight the existence of substantial carbon stocks at depth in grassland soils that are sensitive to management. This is of high relevance globally, given the extent of land cover and large stocks of carbon held in temperate managed grasslands. Our findings have implications for the future management of grasslands for carbon storage and climate mitigation, and for global carbon models which do not currently account for changes in soil carbon to depth with management.

Vascular plants promote ancient peatland carbon loss with climate warming.

Abstract: Northern peatlands have accumulated one third of the Earth's soil carbon stock since the last Ice Age. Rapid warming across northern biomes threatens to accelerate rates of peatland ecosystem respiration. Despite compensatory increases in net primary production, greater ecosystem respiration could signal the release of ancient, century- to millennia-old carbon from the peatland organic matter stock. Warming has already been shown to promote ancient peatland carbon release, but, despite the key role of vegetation in carbon dynamics, little is known about how plants influence the source of peatland ecosystem respiration. Here, we address this issue using in situ (14)C measurements of ecosystem respiration on an established peatland warming and vegetation manipulation experiment. Results show that warming of approximately 1 °C promotes respiration of ancient peatland carbon (up to 2100 years old) when dwarf-shrubs or graminoids are present, an effect not observed when only bryophytes are present. We demonstrate that warming likely promotes ancient peatland carbon release via its control over organic inputs from vascular plants. Our findings suggest that dwarf-shrubs and graminoids prime microbial decomposition of previously 'locked-up' organic matter from potentially deep in the peat profile, facilitating liberation of ancient carbon as CO2. Furthermore, such plant-induced peat respiration could contribute up to 40% of ecosystem CO2 emissions. If consistent across other subarctic and arctic ecosystems, this represents a considerable fraction of ecosystem respiration that is currently not acknowledged by global carbon cycle models. Ultimately, greater contribution of ancient carbon to ecosystem respiration may signal the loss of a previously stable peatland carbon pool, creating potential feedbacks to future climate change.

Plant community controls on short-term ecosystem nitrogen retention

Abstract: Retention of nitrogen (N) is a critical ecosystem function, especially in the face of widespread anthropogenic N enrichment; however, our understanding of the mechanisms involved is limited. Here, we tested under glasshouse conditions how plant community attributes, including variations in the dominance, diversity and range of plant functional traits, influence N uptake and retention in temperate grassland. We added a pulse of (15) N to grassland plant communities assembled to represent a range of community-weighted mean plant traits, trait functional diversity and divergence, and species richness, and measured plant and microbial uptake of (15) N, and leaching losses of (15) N, as a short-term test of N retention in the plant-soil system. Root biomass, herb abundance and dominant plant traits were the main determinants of N retention in the plant-soil system: greater root biomass and herb abundance, and lower root tissue density, increased plant (15) N uptake, while higher specific leaf area and root tissue density increased microbial (15) N uptake. Our results provide novel, mechanistic insight into the short-term fate of N in the plant-soil system, and show that dominant plant traits, rather than trait functional diversity, control the fate of added N in the plant-soil system.

Temperature sensitivity of soil enzymes along an elevation gradient in the Peruvian Andes

Abstract: Soil enzymes are catalysts of organic matter depolymerisation, which is of critical importance for ecosystem carbon (C) cycling. Better understanding of the sensitivity of enzymes to temperature will enable improved predictions of climate change impacts on soil C stocks. These impacts may be especially large in tropical montane forests, which contain large amounts of soil C. We determined the temperature sensitivity (Q10) of a range of hydrolytic and oxidative enzymes involved in organic matter cycling from soils along a 1900 m elevation gradient (a 10 °C mean annual temperature gradient) of tropical montane forest in the Peruvian Andes. We investigated whether the activity (Vmax) of selected enzymes: (i) exhibited a Q10 that varied with elevation and/or soil properties; and (ii) varied among enzymes and according to the complexity of the target substrate for C-degrading enzymes. The Q10 of Vmax for β-glucosidase and β-xylanase increased with increasing elevation and declining mean annual temperature. For all other enzymes, including cellobiohydrolase, N-acetyl β-glucosaminidase and phosphomonoesterase, the Q10 of Vmax did not vary linearly with elevation. Hydrolytic enzymes that degrade more complex C compounds had a greater Q10 of Vmax, but this pattern did not apply to oxidative enzymes because phenol oxidase had the lowest Q10 value of all enzymes studied here. Our findings suggest that regional differences in the temperature sensitivities of different enzyme classes may influence the terrestrial C cycle under future climate warming.

Influence of soil microbiota in nurse plant systems

Abstract: Summary Facilitation by nurse plants is a key process involved in the organization of plant communities and maintenance of biodiversity, particularly in harsh environments. Nurse plants increase plant diversity and productivity in these ecosystems, but our knowledge on the mechanisms through which such facilitation operates is still expanding. Despite growing evidence that soil microbiota impact plant fitness and community dynamics, their role in plant facilitation has been little explored. Here, we synthesize available evidence on the effect of nurse plants on the abundance, composition and activity of soil microbial communities, and the effect of these soil communities on beneficiary plant species. Studies conducted mostly in arid and semi-arid systems show that nurse plants promote the development of differentiated soil microbial communities characterized by a higher microbial abundance and activity, the dominance of competitive bacteria and larger mycorrhizal networks, compared to gaps and to coexisting non-nurses. There is also evidence that differentiated soil microbiota associated with nurse plants has positive effects on the establishment, growth and fitness of beneficiary plant species, although the mechanisms involved remain unclear. We suggest that they include increased nutrient availability for plants, a better use of resources through functional complementarity in the microbial community, soil stabilization and also direct molecular signalling between soil microbes and plants that affect plant defence and plant interactions. Evidence for the role of soil microbiota as mediators of facilitation by nurse plants is growing, but there are still too few studies on which to draw generalizable conclusions. Future studies are needed to assess the effect of plant ontogeny and environmental conditions on soil microbial communities under nurse plants and other coexisting species, and to determine the microbial groups and specific mechanisms involved in facilitation by nurse plants.

The value of trophic interactions for ecosystem function: dung beetle communities influence seed burial and seedling recruitment in tropical forests.

Abstract: Anthropogenic activities are causing species extinctions, raising concerns about the consequences of changing biological communities for ecosystem functioning. To address this, we investigated how dung beetle communities influence seed burial and seedling recruitment in the Brazilian Amazon. First, we conducted a burial and retrieval experiment using seed mimics. We found that dung beetle biomass had a stronger positive effect on the burial of large than small beads, suggesting that anthropogenic reductions in large-bodied beetles will have the greatest effect on the secondary dispersal of large-seeded plant species. Second, we established mesocosm experiments in which dung beetle communities buried Myrciaria dubia seeds to examine plant emergence and survival. Contrary to expectations, we found that beetle diversity and biomass negatively influenced seedling emergence, but positively affected the survival of seedlings that emerged. Finally, we conducted germination trials to establish the optimum burial depth of experimental seeds, revealing a negative relationship between burial depth and seedling emergence success. Our results provide novel evidence that seed burial by dung beetles may be detrimental for the emergence of some seed species. However, we also detected positive impacts of beetle activity on seedling recruitment, which are probably because of their influence on soil properties. Overall, this study provides new evidence that anthropogenic impacts on dung beetle communities could influence the structure of tropical forests; in particular, their capacity to regenerate and continue to provide valuable functions and services.

Influence of plant traits, soil microbial properties, and abiotic parameters on nitrogen turnover of grassland ecosystems

Abstract: Although it is known that multiple interactions among plant functional traits, microbial properties , and abiotic soil parameters influence the nutrient turnover, the relative contribution of each of these groups of variables is poorly understood. We manipulated grassland plant functional composition and soil nitrogen (N) availability in a multisite mesocosm experiment to quantify their relative effects on soil N turnover. Overall, root traits, arbuscular mycorrhizal colonization, denitrification potential, as well as N availability and water availability, best explained the variation in measured ecosystem properties, especially the trade-off between nutrient sequestration and plant biomass production. Their relative contributions varied with soil N availability. In relatively N-poor soils (10–20 μg·N·g −1 soil), N turnover was mainly controlled by microbial properties and abiotic soil parameters, whereas in the relatively N-rich soils (110–120 μg·N·g −1 soil), N turnover was mainly controlled by plant traits and microbial properties. This experiment is a strong demonstration of the importance of functional characteristics of both plants and soil microbes, and their interplay with soil N availability, for N turnover in grassland soils.

Assessing the Importance of Intraspecific Variability in Dung Beetle Functional Traits.

Abstract: Functional diversity indices are used to facilitate a mechanistic understanding of many theoretical and applied questions in current ecological research. The use of mean trait values in functional indices assumes that traits are robust, in that greater variability exists between than within species. While the assertion of robust traits has been explored in plants, there exists little information on the source and extent of variability in the functional traits of higher trophic level organisms. Here we investigated variability in two functionally relevant dung beetle traits, measured from individuals collected from three primary forest sites containing distinct beetle communities: body mass and back leg length. In doing so we too addressed the following questions: (i) what is the contribution of intra vs. interspecific differences in trait values; (ii) what sample size is needed to provide representative species mean trait values; and (iii) what impact does omission of intraspecific trait information have on the calculation of functional diversity (FD) indices from naturally assembled communities? At the population level, interspecific differences explained the majority of variability in measured traits (between 94% and 96%). In accordance with this, the error associated with calculating FD without inclusion of intraspecific variability was low, less than 20% in all cases. This suggests that complete sampling to capture intraspecific variance in traits is not necessary even when investigating the FD of small and/or naturally formed communities. To gain an accurate estimation of species mean trait values we encourage the measurement of 30–60 individuals and, where possible, these should be taken from specimens collected from the site of study.

Grassland invasibility varies with drought effects on soil functioning

Abstract: Summary Although it is known that ecosystems are more susceptible to invasion when disturbed, our knowledge of the mechanisms involved remains limited. Recent studies indicate that disturbance-induced changes in soil nutrient availability could influence community invasibility, but the importance of this mechanism in the real world is not known. We tested the hypotheses that (i) exotic plant species profit from drought effects on soil functioning more than do natives; and (ii) grassland invasibility depends on soil responses to drought disturbance, which are greater in soils that exhibit a larger nutrient pulse following drought. This was tested in a series of grassland sites of contrasting management intensity which we subjected to an extreme (40-day) drought, after which seeds from four different plant families of native species and related exotics were added to soils originating from the drought and control treatments under greenhouse conditions. We also examined the performance of seeded native species in the field. We expected that intensively managed grasslands with bacterial-dominated soils would exhibit a larger nutrient pulse following drought, and hence a greater window of opportunity for invasion, than in extensively managed grassland soils with fungal-dominated microbial communities. Results from the greenhouse experiment indicated that exotic species grew better in soil that had experienced drought, and had higher survival and growth rates than natives in both grassland types. Field results showed that drought increased invasibility in intensively managed grasslands, but had little impact on survival and growth of seeded species on extensively managed grassland soils. Increased invasibility of intensively managed grassland soils was associated with a significant soil nitrogen pulse following rewetting, which was not detected in the extensively managed grasslands. Synthesis. Our results indicate that intensively managed grasslands are more prone to invasion following drought than are extensively managed grasslands and that this response is in part related to differences in microbial community composition which regulate nutrient availability in soil following disturbance events. Given that extreme climate events are predicted to increase, our findings suggest that invasion of exotic species will increase in ecosystems with soils that are less resilient to disturbance.

Warming alters competition for organic and inorganic nitrogen between co-existing grassland plant species

Abstract: Grass species may acquire different forms of nitrogen (N) to reduce competition for the same resources. Climate change influences the availability of soil N and is therefore likely to cause shifts in N forms acquired by plants, thereby affecting their competitive interactions. We investigated the effects of warming on the uptake of different N forms and competitive interactions of Festuca ovina and Anthoxanthum odoratum in a pot experiment. The plants were grown either in monocultures or mixture, and at ambient or elevated temperature (+10 °C), and supplied with 13C and 15N isotopes to test for treatment effects on the relative uptake of ammonium, alanine or tri-alanine. Both grass species took up relatively more N supplied as ammonium than as alanine or tri-alanine when grown under ambient conditions in monoculture. In contrast, when grown in mixtures, F. ovina took up the three supplied N forms in equal amounts, whereas A. odoratum switched to tri-alanine as the main N form. Under warmed conditions, both species took up the N forms equally, irrespective of competition treatments. We have shown that grass species grown in mixture and under ambient conditions reduce competition by acquiring different N forms. Warming increased the availability of inorganic N in the soil and therefore deregulated the need for differential uptake of N forms.

Knowledge needs, available practices, and future challenges in agricultural soils

Abstract: . The goal of this study is to clarify research needs and identify effective practices for enhancing soil health. This was done by a synopsis of soil literature that specifically tests practices designed to maintain or enhance elements of soil health. Using an expert panel of soil scientists and practitioners, we then assessed the evidence in the soil synopsis to highlight practices beneficial to soil health, practices considered detrimental, and practices that need further investigation. A partial Spearman's correlation was used to analyse the panel's responses. We found that increased certainty in scientific evidence led to practices being considered to be more effective due to them being empirically justified. This suggests that for practices to be considered effective and put into practice, a substantial body of research is needed to support the effectiveness of the practice. This is further supported by the high proportion of practices (33 %), such as changing the timing of ploughing or amending the soil with crops grown as green manures, that experts felt had unknown effectiveness, usually due to insufficiently robust evidence. Only 7 of the 27 reviewed practices were considered to be beneficial, or likely to be beneficial in enhancing soil health. These included the use of (1) integrated nutrient management (organic and inorganic amendments); (2) cover crops; (3) crop rotations; (4) intercropping between crop rows or underneath the main crop; (5) formulated chemical compounds (such as nitrification inhibitors); (6) control of traffic and traffic timing; and (7) reducing grazing intensity. Our assessment, which uses the Delphi technique, is increasingly used to improve decision-making in conservation and agricultural policy, identified practices that can be put into practice to benefit soil health. Moreover, it has enabled us to identify practices that need further research and a need for increased communication between researchers, policy-makers, and practitioners, in order to find effective means of enhancing soil health.

Temperature drives plant and soil microbial diversity patterns across an elevation gradient from the Andes to the Amazon

Abstract: 1. Climate strongly regulates plant community composition and diversity, exemplified by gradients in plant diversity and community structure with elevation. However, we do not know if soil bacteria and fungi, key drivers of terrestrial biogeochemical cycling, follow similar biogeographical patterns determined by the same climatic drivers. 2. We studied an Andean tropical forest transect traversing 3.5 km in elevation. The species richness (α-diversity) and compositional dissimilarity of communities (β-diversity) were determined for plants, bacteria and fungi. We determined the environmental drivers of these patterns, using 31 environmental and edaphic predictor variables, and the relationship between microbial communities and soil organic matter cycling (extracellular enzymes). 3. We found co-ordinated changes with elevation in the species richness and composition of plants, soil bacteria and fungi. Across all groups, α-diversity declined significantly as elevation increased, and β-diversity increased with increased elevation difference. Temperature was the dominant driver of these diversity gradients, with only weak influences of edaphic properties, including soil pH, which did not vary substantially across the study transect. The gradients in microbial diversity were strongly correlated with the activities of enzymes involved in soil organic matter cycling, and were accompanied by a transition in microbial traits, towards slower-growing, more oligotrophic taxa at higher elevations. 4. We provide the first evidence of co-ordinated temperature-driven patterns in the diversity and distribution of plants, soil bacteria and fungi in tropical ecosystems. This finding suggest that, across landscape scales of relatively constant soil pH, shared patterns and environmental drivers of plant and microbial communities can occur, with large implications for tropical forest communities under future climate change.

Managing grassland diversity for multiple ecosystem services. Final report, Defra project BD5003

Abstract: The overarching goal of this project was to assess the potential for UK grasslands to deliver multifunctional objectives of carbon (C) sequestration, nutrient retention, pollination and biodiversity conservation, in working farming environments. The main focus of the project was soil C sequestration, and specific objectives were to: (a) assess the C storage potential of grasslands and the sensitivity of this C to management and climate change; and (b) experimentally test the potential to manage grassland vegetation diversity to optimise soil C storage. An additional aim was to test how variation in vegetation diversity and composition in agricultural grassland influences the provision of other ecosystem services, including nitrogen (N) and phosphorus (P) retention in soil, and pollination services, thereby contributing the overall multifunctionality of grassland systems. Our ultimate goal was to develop an improved mechanistic basis for management of C storage alongside other ecosystem services in UK grassland, thereby providing policy relevant tools for managing soil C and offsetting C emissions, with potential benefits for other ecosystem services.