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

种子建立是植物物种生活史中一个关键的人口统计学过程，它影响着植物种群的持续和稳定以及群落聚集过程。近年来，基于性状的方法越来越多地用于了解群落聚集过程的机制及其与生态系统功能的关系。然而，大多数研究都集中在成虫的地上和地下性状上，而在性状生态学中对种子和幼苗性状的研究较少。因此，本项目的主要目标是描述生物多样性探索区草地上多种物种的种子和早期生活史特征，并将这些特征与土地利用对草地多样性和群落聚集过程的影响联系起来。(1)对生物多样性试验区150个试验地在标准化条件下的多种草地物种进行种子形态和化学性状分析，并对其发芽和幼苗性状进行测定。(2)在第二次共同园地试验中，通过控制与草地利用强度相关的环境条件（即凋落物存在和施肥）对种子萌发和幼苗性状的影响，并将其用于新的多草地利用试验中的种子添加试验。(3)定量分析了不同土地利用强度下试验性降低对土壤表层土壤种子库物种丰富度和密度的短期影响，为解释不同土地利用强度下草地植物多样性和群落组成变化提供了重要依据。(4)最后，我们将利用种子和幼苗性状数据，结合生物多样性探索项目的其他数据，测试不同土地利用强度下草地植物物种的发生和丰度与种子再生特征的关系，以及在降低土地利用强度或增加种子时，种子和幼苗性状对群落组装过程的作用。以及种子和幼苗性状多样性与成体植物性状多样性的关系。总而言之，该项目将通过纳入除成虫植物以外的生活史阶段的植物特征，将基于性状的生态学扩展到人口统计学的观点，这些植物特征特别脆弱，因此可能对了解群落聚集过程和维持草原植物多样性至关重要。

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.