Nitrogen Deposition Reduces Plant Diversity and Alters Ecosystem Functioning: Field-Scale Evidence from a Nationwide Survey of UK Heathlands
Power SA (2013) Nitrogen Deposition Reduces Plant Diversity and Alters Ecosystem Functioning: Field-
Scale Evidence from a Nationwide Survey of UK Heathlands. PLoS ONE 8(4): e59031. doi:10.1371/journal.pone.0059031
Nitrogen Deposition Reduces Plant Diversity and Alters Ecosystem Functioning: Field-Scale Evidence from a Nationwide Survey of UK Heathlands
Georgina E. Southon 0 1
Christopher Field 0 1
Simon J. M. Caporn 0 1
Andrea J. Britton 0 1
Sally A. Power 0 1
Minna-Maarit Kyto viita, Jyvaskyla University, Finland
0 1 Division of Biology, Imperial College London, Ascot , Berkshire , United Kingdom , 2 Division of Biology and Conservation Ecology, Manchester Metropolitan University , Manchester , United Kingdom , 3 James Hutton Institute, Craigiebuckler , Aberdeen , United Kingdom, 4 Hawkesbury Institute for the Environment, University of Western Sydney , Penrith New South Wales , Australia
1 N Deposition , Heathland Diversity and Function
Findings from nitrogen (N) manipulation studies have provided strong evidence of the detrimental impacts of elevated N deposition on the structure and functioning of heathland ecosystems. Few studies, however, have sought to establish whether experimentally observed responses are also apparent under natural, field conditions. This paper presents the findings of a nationwide field-scale evaluation of British heathlands, across broad geographical, climatic and pollution gradients. Fifty two heathlands were selected across an N deposition gradient of 5.9 to 32.4 kg ha21 yr21. The diversity and abundance of higher and lower plants and a suite of biogeochemical measures were evaluated in relation to climate and N deposition indices. Plant species richness declined with increasing temperature and N deposition, and the abundance of nitrophilous species increased with increasing N. Relationships were broadly similar between upland and lowland sites, with the biggest reductions in species number associated with increasing N inputs at the low end of the deposition range. Both oxidised and reduced forms of N were associated with species declines, although reduced N appears to be a stronger driver of species loss at the functional group level. Plant and soil biochemical indices were related to temperature, rainfall and N deposition. Litter C:N ratios and enzyme (phenol-oxidase and phosphomonoesterase) activities had the strongest relationships with site N inputs and appear to represent reliable field indicators of N deposition. This study provides strong, field-scale evidence of links between N deposition - in both oxidised and reduced forms - and widespread changes in the composition, diversity and functioning of British heathlands. The similarity of relationships between upland and lowland environments, across broad spatial and climatic gradients, highlights the ubiquity of relationships with N, and suggests that N deposition is contributing to biodiversity loss and changes in ecosystem functioning across European heathlands.
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Funding: This work was funded by the UK Department for Environment, Food and Rural Affairs, under the UKREATE programme (http://ukreate.defra.gov.uk/).
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Human activities associated with the production of energy,
fertilisers and leguminous crops have had a substantial effect on
the global nitrogen (N) cycle [1]. Recent estimates suggest that
anthropogenic contributions to the global reactive N pool have
increased 10-fold since pre-industrial times and are predicted to
double, relative to current day levels, by 2050 [2]. Deposition of N
is spatially highly variable; in Europe, for example, rates currently
range from ,1 kg ha21 yr21 in the relatively pristine areas of
northern Scandinavia to .50 kg ha21 yr21 in areas dominated by
industry (e.g. Northern Italy) or intensive agriculture (e.g.
Netherlands) [3].
The link between N deposition and changes in the structure and
functioning of terrestrial ecosystems is now widely acknowledged,
with N cited as one of the leading drivers of biodiversity loss at a
global scale [4,5]. Manipulation experiments have demonstrated a
wide range of plant responses to N, including changes in plant
phenology, physiology, biochemistry, productivity and assimilate
allocation [68]. Resulting changes in competition between
neighbouring species, as well as N-driven changes in soil pH and
NH4+ concentrations and/or increased sensitivity to
environmental stresses, are believed to be responsible for changes in plant
community composition observed in many ecosystems [9].
Similarly, N-driven changes in the activity and composition of
the soil microbial community [10,11] have been linked with
changes in key soil processes, such as rates of decomposition and
nitrous oxide production [1213], with implications for the
functioning of (...truncated)