Mechanisms of purple moor-grass ( Molinia caerulea) encroachment in dry heathland ecosystems with chronic nitrogen inputs

• Published in: Environmental pollution (1987) 2011-12, Vol.159 (12), p.3553-3559
• Main Authors: Friedrich, Uta, von Oheimb, Goddert, Dziedek, Christoph, Kriebitzsch, Wolf-Ulrich, Selbmann, Katharina, Härdtle, Werner
• Format: Article
• Language: English
• Subjects: Allocations; Animal and plant ecology; Animal, plant and microbial ecology; Asymmetry; Availability; Biological and medical sciences; Biomass; Biomass allocation; Calluna vulgaris; Competition; Dominance; dry matter partitioning; Ecosystem; ecosystems; Fertilizers - analysis; Fundamental and applied biological sciences. Psychology; General aspects; grasses; greenhouse experimentation; Greenhouses; heathlands; Molinia caerulea; N deposition; nitrogen; Nitrogen - metabolism; nitrogen fertilizers; Nutrient sequestration; Poaceae - growth & development; Poaceae - metabolism; seedlings; Shortages; Soil - analysis; Strategy; Synecology; vigor
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2011.08.010

We analysed growth strategies (biomass allocation, nutrient sequestration and allocation) of heather ( Calluna vulgaris) and purple moor-grass ( Molinia caerulea) seedlings in monocultures and mixtures in relation to N, P, and N + P fertilisation in a greenhouse experiment in order to simulate a heath’s pioneer phase under high airborne nitrogen (N) loads. N fertilisation increased the total biomass of both species in monocultures. In mixtures, M. caerulea sequestered about 65% of the N applied, while C. vulgaris suffered from N shortage (halving of the total biomass). Thus, in mixtures only M. caerulea will benefit from airborne N loads, and competition will become increasingly asymmetric with increasing N availability. Our results demonstrate that the heath’s pioneer phase is the crucial tipping point at which the competitive vigour of M. caerulea (high belowground allocation, efficient use of belowground resources, shortened reproductive cycles) induces a shift to dominance of grasses under increased N availability. ► M. caerulea seedlings sequestered about 65% of the N applied in mixtures. ► M. caerulea seedlings stronger respond to N fertilisation than older plants do. ► C. vulgaris seedlings halved their biomass in mixtures as a result of N shortage. ► In mixtures, only M. caerulea will benefit from airborne N loads. The present study indicates that the heath’s pioneer phase is the crucial tipping point at which a shift to dominance of purple moor-grass occurs under increased N availability.