Showing papers by "Richard D. Bardgett published in 2005"

A temporal approach to linking aboveground and belowground ecology

Abstract: Ecologists are becoming increasingly aware of the role of aboveground–belowground relationships in controlling ecosystem processes and properties. Here, we review recent studies that show that relationships between aboveground and belowground communities operate over a hierarchy of temporal scales, ranging from days to seasons, to millennia, with differing consequences for ecosystem structure and function. We propose that a temporal framework is crucial to our understanding of the nature and ecological significance of relationships between aboveground and belowground communities.

The biology of soil : a community and ecosystem approach.

Abstract: Preface and acknowledgements 1. The soil environment 2. The diversity of life in soil 3. Organism interactions and soil processes 4. Linkages between plant and soil biological communities 5. Above-ground trophic interactions and soil biological communities 6. Soil biological properties and global change 7. Conclusions Bibliography Index

Preferential uptake of soil nitrogen forms by grassland plant species

Abstract: In this study, we assessed whether a range of temperate grassland species showed preferential uptake for different chemical forms of N, including inorganic N and a range of amino acids that commonly occur in temperate grassland soil. Preferential uptake of dual-labelled (13C and 15N) glycine, serine, arginine and phenylalanine, as compared to inorganic N, was tested using plants growing in pots with natural field soil. We selected five grass species representing a gradient from fertilised, productive pastures to extensive, low productivity pastures (Lolium perenne, Holcus lanatus, Anthoxanthum odoratum, Deschampsia flexuosa, and Nardus stricta). Our data show that all grass species were able to take up directly a diversity of soil amino acids of varying complexity. Moreover, we present evidence of marked inter-species differences in preferential use of chemical forms of N of varying complexity. L. perenne was relatively more effective at using inorganic N and glycine compared to the most complex amino acid phenylalanine, whereas N. stricta showed a significant preference for serine over inorganic N. Total plant N acquisition, measured as root and shoot concentration of labelled compounds, also revealed pronounced inter-species differences which were related to plant growth rate: plants with higher biomass production were found to take up more inorganic N. Our findings indicate that species-specific differences in direct uptake of different N forms combined with total N acquisition could explain changes in competitive dominance of grass species in grasslands of differing fertility.

Biological Diversity and Function in Soils

Abstract: Although soil provides physical support for plants and contributes to a variety of important environmental functions, many questions about the ecological significance of its biological diversity, and how ecosystem function is affected, have never been asked. Recent technical developments, as well as new experimental and modelling approaches, have led to a renaissance in soil biodiversity research. The key areas are reflected in this new volume, which brings together many leading contributions on the role and importance of soil biota.

Soil Invertebrates Disrupt Carbon Flow Through Fungal Networks

Abstract: Annual carbon flux through soil respiration is ten times greater than fossil fuel combustion, but its component parts are poorly understood because they are the product of complex multitrophic interactions between soil organisms. A major component of carbon flux from plants to soil occurs through networks of symbiotic arbuscular mycorrhizal fungi. Here, using 13CO2 pulse labeling, we show that natural densities of the numerically dominant fungal feeding invertebrate Protaphorura armata (order Collembola) reduces 13C enrichment of mycorrhizosphere respiration by 32%. Our findings emphasize the importance of multitrophic interactions in regulating respiration of recent plant photosynthate from soil.

Rising Atmospheric CO2 Reduces Sequestration of Root-Derived Soil Carbon

Abstract: Forests have a key role as carbon sinks, which could potentially mitigate the continuing increase in atmospheric carbon dioxide concentration and associated climate change. We show that carbon dioxide enrichment, although causing short-term growth stimulation in a range of European tree species, also leads to an increase in soil microbial respiration and a marked decline in sequestration of root-derived carbon in the soil. These findings indicate that, should similar processes operate in forest ecosystems, the size of the annual terrestrial carbon sink may be substantially reduced, resulting in a positive feedback on the rate of increase in atmospheric carbon dioxide concentration.

Patterns and determinants of soil biological diversity

Abstract: SUMMARY This chapter examines the vast diversity of organisms that live in the soil and discusses the various factors that regulate its spatial and temporal patterning. There is a dearth of information available on the diversity of soil biota, especially at the species level, but existing data provide little support for the idea that the same forces that regulate patterns of diversity above-ground (i.e. productivity and disturbance) control patterns of biodiversity below-ground, or that regional-scale patterns of soil biodiversity show similar trends to those that occur above-ground. We argue that patterning of soil biodiversity is related primarily to the heterogeneous nature, or patchiness, of the soil environment at different spatial and temporal scales, and that this heterogeneity provides unrivalled potential for niche partitioning, or resource and habitat specialisation, leading to avoidance of competition and hence co-existence of species. We highlight the challenge for soil ecologists to identify the hierarchy of controls on soil biological diversity that operate at different spatial and temporal scales, and to determine the role of spatio-temporal patterning of soil biodiversity as a driver of above-ground community assembly and productivity. Introduction The Earth hosts a bewildering diversity of organisms that are distributed in a wide variety of spatial and temporal patterns across, and within, the Earth's ecosystems. Making sense of these complex patterns of diversity, and understanding the dominant forces that control them, has been a major theme of community ecology (Huston 1994).

Relating microarthropod community structure and diversity to soil fertility manipulations in temperate grassland

Abstract: We aimed to identify patterns of diversity in a below-ground community of microarthropods (mites and Collembola) after 15 months of a nutrient (calcium and nitrogen) manipulation experiment, located at the Natural Environment Research Council (NERC) Soil Biodiversity Site in Scotland, UK. We found that microarthropod densities increased with elevated soil fertility, but we detected no concurrent change in the diversity of soil microarthropods (mites and Collembola combined). That microarthropod density increased concurrently with improvements in soil fertility and plant productivity suggests that soil microarthropod communities are predominately regulated by bottom-up forces, driven by increased energy transfer via plant inputs to soil, providing increased food resources for fauna. However, that we found no concurrent change in the diversity of soil microarthropods provides little support for the idea that the diversity of soil fauna is positively related to their population density, primary productivity or improvements in soil conditions resulting from nutrient manipulations. However, we did find that microarthropod communities of more fertile sites contained a greater proportion of predators suggesting that more energy was transferred to higher trophic levels under elevated soil fertility. Our findings suggest that unlike plant communities, soil faunal diversity may not be strongly regulated by competition in productive situations, since competitive exclusion might not occur due to increased predation. Whilst we conclude that soil microarthropod diversity at our study site has not been affected by the nutrient additions to date, in the longer term we predict that changes in community composition and diversity could arise, most likely through top-down regulation of the soil food web.

The Effects of Spatial Scale on Trophic Interactions

Abstract: Food chain models have dominated empirical studies of trophic interactions in the past decades, and have lead to important insights into the factors that control ecological communities. Despite the importance of food chain models in instigating ecological investigations, many empirical studies still show a strong deviation from the dynamics that food chain models predict. We present a theoretical framework that explains some of the discrepancies by showing that trophic interactions are likely to be strongly influenced by the spatial configuration of consumers and their resources. Differences in the spatial scale at which consumers and their resources function lead to uncoupling of the population dynamics of the interacting species, and may explain overexploitation and depletion of resource populations. We discuss how changed land use, likely the most prominent future stress on natural systems, may affect food web dynamics by interfering with the scale of interaction between consumers and their resource.

Large herbivores affect the stoichiometry of nutrients in a regenerating woodland ecosystem.

Abstract: Previous studies on the effects of herbivores on nutrient cycling have given little consideration to the relationship between soil nitrogen (N) and phosphorus (P) availability. Here we examined how browsing by red deer influences the relative availability of N and P in a regenerating woodland ecosystem. We found that removal of browsing by fencing for 14 years led to a shift from N toward P limitation of the dominant tree species Betula pubescens. This was evidenced by a significant increase in foliar N:P ratio of B. pubescens as a result of removal of browsing; mean N:P ratio of foliage from browsed areas was 13.2 suggesting that trees growing in browsed areas were N limited, whereas foliage from unbrowsed areas had a mean N:P ratio of 15.8, suggesting that these areas were more P limited. Further evidence of a shift toward P limitation in unbrowsed areas came from the finding that root uptake of labelled 32P was significantly greater in roots collected from unbrowsed than browsed trees. Soil phosphatase activity did not significantly differ between browsed and unbrowsed areas. Our data indicate therefore that herbivores have the potential to significantly affect the stoichiometry of N and P in forest ecosystems.

The balance between productivity and food web structure in soil ecosystems.

Abstract: PART III Patterns and drivers of soil biodiversity 5 The use of model Pseudomonas fluorescens populations to study the causes and consequences of microbial diversity 83 Paul B. Rainey, Michael Brockhurst, Angus Buckling, David J. Hodgson and Rees Kassen 6 Patterns and determinants of soil biological diversity 100 Richard D. Bardgett, Gregor W. Yeates and Jonathan M. Anderson 7 How plant communities influence decomposer communities 119 David A. Wardle 8 The balance between productivity and food web structure in soil ecosystems 139 Peter C. de Ruiter, Anje-Margriet Neutel and John Moore

Changes in tree growth resulting from simulated browsing have limited effects on soil biological properties

Abstract: Herbivores can indirectly affect ecosystem productivity by modifying feedbacks that occur between dominant plants and below-ground properties, especially through altering nutrient availability in soil. The aim of this study was to examine, under controlled conditions, the effect of simulated browsing by large herbivores on the growth characteristics of downy birch (Betula pubescens), a dominant tree species of native regenerating forests in northern Britain, and to determine how effects of browsing on tree growth cascaded through to soil microbial communities, thereby affecting nutrient availability in soil. Downy birch seedlings were grown in mesocosms for 2 years and subjected to simulated browsing in the form of defoliation and clipping treatments. Upon destructive harvest, a number of measures of both tree growth characteristics and soil biological and nutrient properties were made. Clipping of birch trees significantly reduced total root biomass (27%), fine root biomass (29%), coarse root biomass (27%) and above-ground biomass (18%), whereas defoliated trees were significantly shorter than non-defoliated trees. Despite these significant and negative effects of browsing on tree growth, soil biological properties remained largely unaffected, other than rates of N mineralisation, which were greater under defoliated trees. We conclude that other factors, such as herbivore effects on litter quantity and quality which feedback to soil biological properties in the longer-term are more important in determining ecosystem responses to browsing.

Response to comment on "Ecosystem properties and forest decline in contrasting long-term chronosequences"

Abstract: Kitayama ([ 1 ][1]) correctly recognizes that the six forested chronosequences we studied ([ 2 ][2]) do not include any of the hyperdiverse forests commonly found in the tropics. We welcome others to test whether the patterns we found for our six sites also occur in other systems and also recognize

Trophic interactions in a changing world : the role of spatial scale.

Abstract: Food chain models have dominated empirical studies of trophic interactions in the past decades, and have lead to important insights into the factors that control ecological communities. Despite the importance of food chain models in instigating ecological investigations, many empirical studies still show a strong deviation from the dynamics that food chain models predict. We present a theoretical framework that explains some of the discrepancies by showing that trophic interactions are likely to be strongly influenced by the spatial configuration of consumers and their resources. Differences in the spatial scale at which consumers and their resources function lead to uncoupling of the population dynamics of the interacting species, and may explain overexploitation and depletion of resource populations. We discuss how changed land use, likely the most prominent future stress on natural systems, may affect food web dynamics by interfering with the scale of interaction between consumers and their resource.