title: Mechanisms of purple moor-grass (Molinia caerulea) encroachment in dry heathland ecosystems with chronic nitrogen inputs.
abstract: 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.
authors.affiliation: Institute of Ecology, University of Lüneburg, Scharnhorststr 1, 21335 Lüneburg, Germany. uta.friedrich@leuphana.de
authors.forename: Uta
authors.initials: U
authors.lastname: Friedrich
authors.forename: Goddert
authors.initials: G
authors.lastname: von Oheimb
authors.forename: Christoph
authors.initials: C
authors.lastname: Dziedek
authors.forename: Wolf-Ulrich
authors.initials: WU
authors.lastname: Kriebitzsch
authors.forename: Katharina
authors.initials: K
authors.lastname: Selbmann
authors.forename: Werner
authors.initials: W
authors.lastname: Härdtle
mesh_terms: D018533:Biomass; D017753:Ecosystem; D005308:Fertilizers / Q000032:analysis; D009584:Nitrogen / Q000378:metabolism*; D006109:Poaceae / Q000254:growth & development* / Q000378:metabolism*; D012987:Soil / Q000032:analysis
chemical_list: D005308:Fertilizers; D012987:Soil; D009584:Nitrogen