Different from the start: key dimensions of seedling traits of central European temperate grassland species

Plant traits and their tradeoffs are major determinants of plant functions. Although trait‐based frameworks should apply to plant functioning at any life stage, they have been primarily established for adult plants. Therefore, we lack comprehensive trait‐based studies of seedlings across multiple species to prove which key dimensions of trait variation are already differentiated early in the plant life cycle. We studied germination phenology and growth‐related morphological above‐ and below‐ground traits of seedlings of 180 temperate grassland species in microcosms under ambient light and temperature conditions. We found that key dimensions of functional specialization involving the leaf and root conservation gradient, the plant size gradient, and the root collaboration gradient are already apparent in seedlings. The root collaboration gradient converged with the plant size gradient, implying that only some growth strategies of seedlings resemble those of adult plants. The slow end of the leaf and root conservation gradient was largely associated with high root‐to‐shoot ratios. An independent third axis emerged, attributable to variation in the timing of germination. Seed mass had positive relationships with slow traits of the conservation gradient and the outsourcing strategy of the collaboration gradient, supporting the importance of seed reserves. Seedling growth rates were largely influenced by temperature, but were additionally positively related to seed mass. Our findings underpin that trait spectra of seedlings already reflect some well‐known tradeoffs related to plant tissue construction and resource allocation, but do not simply mirror those of adult plants. The unrelatedness of germination phenology with growth‐related morphological traits further diversifies ecological strategies in the earliest plant life stage. Our results call for further work to identify the generality of functional tradeoffs across the plant life cycle.