Seed and seedling traits as related to plant diversity and community assembly in grasslands at different land-use intensity

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Establishment from seeds is a key demographic process in the life-history of plant species, which influences the persistence and stability of plant populations and processes of community assembly. In recent years, trait-based approaches are increasingly used to understand the mechanisms underlying processes of community assembly and its relationships to ecosystem functioning. However, most studies have focused on above- and belowground traits of adult plants, while traits of seeds and seedlings have received much less attention in trait-based ecology. Therefore, this project has the major goal to characterize seed and early life-history traits of multiple species occurring in the grasslands of the Biodiversity Exploratories and relate these traits to land-use effects on grassland diversity and processes of community assembly. The following specific objectives will be addressed: (1) Morphological and chemical seed traits will be analyzed and germination and seedling traits will be measured for multiple grassland species that occur in the 150 experimental plots of the Biodiversity Exploratories under standardized conditions in a common garden experiment. (2) The effects of environmental conditions, which are related to land-use intensity of grasslands, i.e. litter presence and fertilization, on germination and seedling traits will be measured by manipulating these factors in a second common garden experiment for all species, which will be used for the seed addition experiment in the new multi-grassland land-use experiment. (3) The short-term effects of experimental reduction of land-use intensity on species richness and density of the viable seed bank in the top soil of the sites included in the new multi-grassland land-use experiment will be quantified to contribute variables related to demographic storage as an important aspect in explaining shifts in plant diversity and composition of the grassland communities in response to reduced land-use intensity. (4) Finally, we will use data on seed and seedling traits, in combination with other data from the Biodiversity Exploratories, to test how the occurrence and abundance of plant species in grassland of different land-use intensity relates to traits characterizing regeneration from seeds, to test for the role of seed and seedling traits for community assembly processes when land-use intensity is reduced or seeds are added, and how measures of diversity of seed and seedling traits relate to trait diversity of adult plants. In summary, the project will contribute to an extension of trait-based ecology to a demographic perspective by incorporating plant traits of life-history stages other than adult plants, which are particularly vulnerable and might therefore be essential to understand processes of community assembly and the maintenance of grassland plant diversity.