Functional Relationships with N Deposition Differ According to Stand Maturity in Calluna-Dominated Heathland
Plant and soil bio(chemical) indicators are increasingly used to provide information on N deposition inputs and effects in a wide range of ecosystem types. However, many factors, including climate and site management history, have the potential to influence bioindicator relationships with N due to nutrient export and changing vegetation nutrient demands. We surveyed 33 heathlands in England, along a gradient of background N deposition (7.2–24.5 kg ha−1 year−1), using Calluna vulgaris growth phase as a proxy for time since last management. Our survey confirmed soil nutrient accumulation with increasing time since management. Foliar N and phosphorus (P) concentrations in pioneer- and mature-phase vegetation significantly increased with N deposition. Significant interactions between climate and N deposition were also evident with, for example, higher foliar P concentrations in pioneer-phase vegetation at sites with higher temperatures and N deposition rates. Although oxidized N appeared more significant than reduced N, overall there were more, stronger relationships with total N deposition; suggesting efforts to control all emissions of N (i.e., both oxidized and reduced forms) will have ecological benefits.
KeywordsHabitat management Oxidized N Reduced N Lowland heathland Calluna growth phase Bioindicators
The authors gratefully acknowledge the support and permission for site access given by the owners and managers of sites visited during this survey. We are also grateful to Ron Smith (CEH Edinburgh) for provision of modeled N deposition data for survey sites and to Dr. Emma Green for guidance in analytical techniques. This project was funded by the UK Department for Environment, Food and Rural Affairs, as part of the UKREATE programme (Contract Number CPEA18).
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