Michael G. Pilkington

The University of Sheffield, Sheffield, England, United Kingdom

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Publications (11)50.04 Total impact

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    ABSTRACT: Parasitic plants have major impacts on plant community structure through their direct negative influence on host productivity and competitive ability. However, the possibility that these parasites may also have indirect impacts on community structure (via the mechanism of nutrient-rich litter input) while long hypothesized, has remained unsupported until now. Using the hemiparasite Rhinanthus minor, we established experimental grassland mesocosms to quantify the impacts of Rhinanthus litter and parasitism across two soil fertility levels. We measured the biomass and tissue nutrient concentration of three functional groups within these communities to determine their physiological response to resource abstraction and litter input by the parasite. We show that Rhinanthus alters the biomass and nutrient status of co-occurring plants with contrasting effects on different functional groups via the mechanism of nutrient-rich litter input. Critically, in the case of grass and total community biomass, this partially negates biomass reductions caused directly by parasitism. This demonstrates that the influence of parasitic plant litter on plant community structure can be of equal importance to the much-reported direct impacts of parasitism. We must consider both positive indirect (litter) and negative direct (parasitism) impacts of parasitic plants to understand their role in structuring plant communities.
    No preview · Article · Jan 2013 · New Phytologist
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    ABSTRACT: Atmospheric nitrogen (N) deposition is a global and increasing threat to biodiversity and ecosystem function. Much of our current understanding of N deposition impacts comes from field manipulation studies, although interpretation may need caution where simulations of N deposition (in terms of dose, application rate and N form) have limited realism. Here, we review responses to simulated N deposition from the UKREATE network, a group of nine experimental sites across the UK in a diversity of heathland, grassland, bog and dune ecosystems which include studies with a high level of realism and where many are also the longest running globally on their ecosystem type. Clear responses were seen across the sites with the greatest sensitivity shown in cover and species richness of bryophytes and lichens. Productivity was also increased at sites where N was the limiting nutrient, while flowering also showed high sensitivity, with increases and declines seen in dominant shrub and forb species, respectively. Critically, these parameters were responsive to some of the lowest additional loadings of N (7.710 kg ha-1 yr-1) showing potential for impacts by deposition rates seen in even remote and unpolluted regions of Europe. Other parameters were less sensitive, but nevertheless showed response to higher doses. These included increases in soil %N and plant available KCl extractable N, N cycling rates and acidbase status. Furthermore, an analysis of accumulated dose that quantified response against the total N input over time suggested that N impacts can build up within an ecosystem such that even relatively low N deposition rates can result in ecological responses if continued for long enough. Given the responses have important implications for ecosystem structure, function, and recovery from N loading, the clear evidence for impacts at relatively low N deposition rates across a wide range of habitats is of considerable concern.
    Full-text · Article · Apr 2012 · Global Change Biology
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    ABSTRACT: Air pollutants are recognised as important agents of ecosystem change but few studies consider the effects of multiple pollutants and their interactions. Here we use ordination, constrained cluster analysis and indicator value analyses to identify potential environmental controls on species composition, ecological groupings and indicator species in a gradient study of UK acid grasslands. The community composition of these grasslands is related to climate, grazing, ozone exposure and nitrogen deposition, with evidence for an interaction between the ecological impacts of base cation and nitrogen deposition. Ozone is a key agent in species compositional change but is not associated with a reduction in species richness or diversity indices, showing the subtly different drivers on these two aspects of ecosystem degradation. Our results demonstrate the effects of multiple interacting pollutants, which may collectively have a greater impact than any individual agent.
    No preview · Article · Jun 2011 · Environmental Pollution
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    ABSTRACT: Pilkington, M.G. et al. Impacts of burning and increased nitrogen deposition on nitrogen pools and leaching in an upland moor. Journal of ecology, 2007, vol. 95, no. 6, 1195-1207. Published by and copyright Wiley-Blackwell Publishing Ltd. The definitive version of this article is available from http://www.blackwellpublishing.com/journals/JEC 1. Upland moorlands are an extensive semi-natural resource, frequently burned either through management or uncontrolled outbreaks of fire. These systems are often situated in areas receiving high levels of atmospheric nitrogen (N) deposition, yet the effects of burning combined with high N deposition on ecosystem N pools and N leaching to surface waters are unknown. 2. A management burn was applied to an upland Calluna vulgaris moor which contained a set of long-term experimental plots treated with simulated increased N deposition at rates of +0, +40, +80 and +120 kg ha−1 year−1. Leaching losses of total dissolved inorganic N (TDNin) and dissolved organic N (DON) from organic and mineral soil horizons and the N pools in these horizons, as well as in litter and vegetation, were compared before and after the burn. 3. The results showed that leaching of TDNin and DON from both soil horizons increased in a 6-month period after the burn, with leaching of TDNin remaining elevated 2–3 years later. N pools in the deeper mineral layer of the soil also increased after the burn. Increasing long-term N additions magnified the burn effect on leaching losses but lessened the burn effect on the N pools in the mineral layer. In the +40 N addition plots, the amount of N removed in burning vegetation was of an equivalent size to the amount of additional N retained within the system. 4. Synthesis: These results suggest that burning approximately every 10 years may be effective in removing N retained in the system at N deposition rates up to 56 kg N ha−1 year−1. However, extensive burning of moorland or uncontrolled outbreaks of fire over wide areas may considerably exacerbate the threat of N loading to groundwater in areas where moors are more heavily N polluted, increasing the potential for acidification, eutrophication and brown water colouration. The data suggest that this is because the mineral horizon of upland moors receiving high N inputs has already been saturated with N such that increased downward percolation rates of N caused by the burn have risen above a threshold for immobilization (hence leading to more substantial post-burn increases in leaching of N).
    Full-text · Article · Sep 2007 · Journal of Ecology
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    ABSTRACT: On an upland moor dominated by pioneer Calluna vulgaris and with an understorey of mosses and lichens, experimental plots were treated with factorial combinations of nitrogen (N) at +0 and +20 kg N ha−1 yr−1, and phosphorus (P) at +0 and +5 kg P ha−1 yr−1. Over the 4-year duration of the experiment, the cover of the Calluna canopy increased in density over time as part of normal phenological development. Moss cover increased initially in response to N addition but then remained static; increases in cover in response to P addition became stronger over time, eventually causing reductions in the cover of the dominant Calluna canopy. Lichen cover virtually disappeared within 4 years in plots receiving +20 kg N ha−1 yr−1 and also in separate plots receiving +10 kg N ha−1 yr−1, but this effect was reversed by the addition of P.
    Full-text · Article · Jul 2007 · Environmental Pollution
  • C D Evans · S J M Caporn · J.A. Carroll · M G Pilkington · D B Wilson · N Ray · N Cresswell
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    ABSTRACT: A simple model of nitrogen (N) saturation, based on an extension of the biogeochemical model MAGIC, has been tested at two long-running heathland N manipulation experiments. The model simulates N immobilisation as a function of organic soil C/N ratio, but permits a proportion of immobilised N to be accompanied by accumulation of soil carbon (C), slowing the rate of C/N ratio change and subsequent N saturation. The model successfully reproduced observed treatment effects on soil C and N, and inorganic N leaching, for both sites. At the C-rich upland site, N addition led to relatively small reductions in soil C/N, low inorganic N leaching, and a substantial increase in organic soil C. At the C-poor lowland site, soil C/N ratio decreases and N leaching increases were much more dramatic, and soil C accumulation predicted to be smaller. The study suggests that (i) a simple model can effectively simulate observed changes in soil and leachate N; (ii) previous model predictions based on a constant soil C pool may overpredict future N leaching; (iii) N saturation may develop most rapidly in dry, organic-poor, high-decomposition systems; and (iv) N deposition may lead to significantly enhanced soil C sequestration, particularly in wet, nutrient-poor, organic-rich systems.
    No preview · Article · Nov 2006 · Environmental Pollution
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    ABSTRACT: Deposition of reactive nitrogen (N) compounds has the potential to cause severe damage to sensitive soils and waters, but the process of ‘nitrogen saturation’ is difficult to demonstrate or predict. This study compares outputs from a simple carbon–nitrogen model with observations of (1) regional- and catchment-scale relationships between surface water nitrate and dissolved organic carbon (DOC), as an indicator of catchment carbon (C) pool; (2) inter-regional variations in soil C/N ratios; and (3) plot scale soil and leachate response to long-term N additions, for a range of UK moorlands. Results suggest that the simple model applied can effectively reproduce observed patterns, and that organic soil C stores provide a critical control on catchment susceptibility to enhanced N leaching, leading to high spatial variability in the extent and severity of current damage within regions of relatively uniform deposition. Results also support the hypothesis that the N richness of organic soils, expressed as C/N ratio, provides an effective indicator of soil susceptibility to enhanced N leaching. The extent to which current C/N is influenced by N deposition, as opposed to factors such as climate and vegetation type, cannot be unequivocally determined on the basis of spatial data. However, N addition experiments at moorland sites have shown a reduction in organic soil C/N. A full understanding of the mechanisms of N-enrichment of soils and waters is essential to the assessment of current sensitivity to, and prediction of future damage from, globally increasing reactive nitrogen deposition.
    No preview · Article · Mar 2006 · Ecosystems
  • M G Pilkington · S J M Caporn · JA Carroll · N Cresswell · JA Lee · B Reynolds · BA Emmett
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    ABSTRACT: This study was designed to investigate the effect of long-term (11 years) ammonium nitrate additions on standing mass, nutrient content (% and kg ha(-1)), and the proportion of the added N retained within the different compartments of the system. The results showed that more than 90% of all N in the system was found in the soil, particularly in the organic (Oh) horizon. Added N increased the standing mass of vegetation and litter and the N content (kg N ha(-1)) of almost all measured plant, litter and soil compartments. Green tissue P and K content (kg ha(-1)) were increased, and N:P ratios were increased to levels indicative of P limitation. At the lowest treatment, most of the additional N was found in plant/litter compartments, but at higher treatments, there were steep increases in the amount of additional N in the underlying organic and mineral (Eag) horizons. The budget revealed that the proportion of added N found in the system as a whole increased from 60%, 80% and up to 90% in response to the 40, 80 and 120 kg N ha(-1) year(-1) treatments, respectively.
    No preview · Article · Jan 2006 · Environmental Pollution
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    M G Pilkington · S J M Caporn · JA Carroll · N Cresswell · JA Lee · BA Emmett · D Johnson
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    ABSTRACT: This study determined the effects of increased N deposition on rates of N and P transformations in an upland moor. The litter layer and the surface of the organic Oh horizon were taken from plots that had received long-term additions of ammonium nitrate at rates of 40, 80 and 120 kg N ha(-1) yr(-1). Net mineralisation processes were measured in both field and laboratory incubations. Soil phosphomonoesterase (PME) activity and rates of N(2)O release were measured in laboratory incubations and root-surface PME activity measured in laboratory microcosms using Calluna vulgaris bioassay seedlings. Net mineralisation rates were relatively slow, with net ammonification consistently stimulated by N addition. Net nitrification was marginally stimulated by N addition in the laboratory incubation. N additions also increased soil and root-surface (PME) activity and rates of N(2)O release. Linear correlations were found between litter C:N ratio and all the above processes except net nitrification in field incubations. When compared with data from a survey of European forest sites, values of litter C:N ratio were greater than a threshold below which substantial, N input-related increases in net nitrification rates occurred. The maintenance of high C:N ratios with negligible rates of net nitrification was associated with the common presence of ericaceous litter and a mor humus layer in both this moorland as well as the forest sites.
    Full-text · Article · Jul 2005 · Environmental Pollution
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    ABSTRACT: This study was designed to investigate the leaching response of an upland moorland to long-term (10 yr) ammonium nitrate additions of 40, 80 and 120 kg N ha(-1) yr(-1) and to relate this response to other indications of potential system damage, such as acidification and cation displacement. Results showed increases in nitrate leaching only in response to high rates of N input, in excess of 96 and 136 kg total N input ha(-1) yr(-1) for the organic Oh horizon and mineral Eag horizon, respectively. Individual N additions did not alter ammonium leaching from either horizon and ammonium was completely retained by the mineral horizon. Leaching of dissolved organic nitrogen (DON) from the Oh horizon was increased by the addition of 40 kg N ha(-1) yr(-1), but in spite of increases, retention of total dissolved nitrogen reached a maximum of 92% and 95% of 80 kg added N ha(-1) yr(-1) in the Oh and Eag horizons, respectively. Calcium concentrations and calcium/aluminium ratios were decreased in the Eag horizon solution with significant acidification mainly in the Oh horizon leachate. Nitrate leaching is currently regarded as an early indication of N saturation in forest systems. Litter C:N ratios were significantly lowered but values remained above a threshold predicted to increase leaching of N in forests.
    No preview · Article · Jun 2005 · Environmental Pollution
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    ABSTRACT: The results from three long-term field manipulation studies of the impacts of increased nitrogen deposition (0–120 kg N ha–1 yr–1) on lowland and upland heathlands in the UK were compared, to test if common responses are observed. Consistent increases in Calluna foliar N content and decreases in litter C:N ratios were found across all sites, while increases in N leaching were not observed at any site over the range 0–80 kg ha–1 yr–1. However, the response of Calluna biomass did vary between sites, possibly reflecting site differences in nutrient status and management histories. Five versions of a simulation model of heathland responses to N were developed, each reflecting different assumptions about the fate and turnover of soil N. Model outputs supported the deduction from mass balance calculations at two of the field sites that N additions have resulted in an increase in immobilisation; the latter was needed to prevent the model overestimating measured N leaching. However, this version of the model significantly underestimated Calluna biomass. Model versions, which included uptake of organic N by Callunaand re-mobilisation of N from the soil organic store provided some improvement in the fit between modelled and field biomass data, but re-mobilisation also led to an overestimation of N leaching. Quantification of these processes and their response to increased N deposition are therefore critical to interpreting experimental data and predicting the long-term impacts of atmospheric deposition on heathlands and moorlands.
    No preview · Article · Nov 2004 · Water, Air, & Soil Pollution: Focus

Publication Stats

433 Citations
50.04 Total Impact Points


  • 2011-2013
    • The University of Sheffield
      • Department of Animal and Plant Sciences
      Sheffield, England, United Kingdom
  • 2004-2007
    • Manchester Metropolitan University
      • School of Science and The Environment
      Manchester, England, United Kingdom