Nitrogen deposition and soil carbon content affect nitrogen mineralization during primary succession in acid inland drift sand vegetation

Background and aims Two inland dunes in the Netherlands receiving low (24) and high (41 kg N ha⁻¹ yr⁻¹) nitrogen (N) deposition were compared for N dynamics and microbial activity to investigate the potential effect of N on succession rate of the vegetation and loss of pioneer habitats. Methods Primary succession stages were sampled, including bare sand, and vegetation dominated by Polytrichum piliferum, Campylopus introflexus, lichens and grasses respectively, representing a series of vegetation types in undisturbed drift sand sites with succession starting on bare sand containing virtually no organic matter. Microbial characteristics and potential N mineralization were analysed in a laboratory experiment. Results Organic matter accumulated during succession, resulting in a lower pH and in higher microbial biomass (bacteria and fungi), respiration and net N mineralization. The increase in respiration and N mineralization was largely due to the development of an ectorganic layer in the middle stages of succession. The observed effects of N deposition were (1) decrease of microbial biomass, (2) higher net N mineralization per m², (3) higher levels of free nitrogen in the soil, and (4) a higher microbial N:P ratio. Conclusions Elevated N deposition leads to higher N availability which may cause accelerated succession.