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Raised atmospheric CO2 levels affect soil seed bank composition of temperate grasslands

Seibert, Ruben, Grünhage, Ludger, Müller, Christoph, Otte, Annette, Donath, Tobias W.
Journal of vegetation science 2019 v.30 no.1 pp. 86-97
asexual reproduction, buried seeds, carbon dioxide, climate change, ecosystem services, free air carbon dioxide enrichment, germination, grasslands, multidimensional scaling, plant communities, seed longevity, seedlings, soil, species diversity, Germany
QUESTIONS: Soil seed banks buffer plant populations against environmental variability. But environmental changes can have profound impact on them. Several studies addressed the effect of climate change on aboveground vegetation, but studies on changes in the seed bank are rare. Thus, we studied the seed bank of a temperate grassland at a long‐term FACE (Free‐Air Carbon dioxide Enrichment) site, with the following questions: (a) Are there general differences in the species composition between aboveground vegetation and seed bank; (b) what are the impacts of elevated CO₂ (eCO₂) on seed density and species composition of the seed bank; and (c) are there differences in the functional traits of the seed bank species under eCO₂ versus ambient CO₂ (aCO₂)? LOCATION: Temperate grassland, Gießen, Germany. METHOD: Thirty soil cores were taken in six FACE rings. Emerging seedlings were identified to species level after germination and aboveground vegetation was sampled. From the seed bank data, we derived diversity measures and weighted means of species traits, e.g., seed longevity and regeneration type, and compared eCO₂ (+20% CO₂ above ambient conditions) with aCO₂ treatment. RESULTS: Nonmetric multidimensional scaling ordination revealed a clear separation between seed bank and aboveground vegetation but no clear CO₂ effect. Analyses revealed higher seed densities under eCO₂. Species diversity and Shannon diversity were not significantly affected. Evenness decreased significantly under eCO₂. There are shifts in functional traits of seed bank species. Seed density of long‐term‐persistent species increased, while short‐term‐persistent species decreased. Seed densities of species with generative reproduction increased under eCO₂, while numbers of species with vegetative reproduction decreased. CONCLUSION: The observed trait compositions of the seed bank under eCO₂ indicate that species relying on generative reproduction and production of long‐term‐persistent seeds have a competitive advantage under eCO₂. The changes in the plant communities described above may lead to profound changes in the supply of grassland ecosystem services.