Nutrient enrichment degrades soil seed banks
Seed banks are hidden biodiversity reservoirs in the soil that are believed to increase resilience of grassland ecosystems to global changes, such as nutrient enrichment and loss of grazing. A recent study published in Nature Communications, led by associate professor Anu Eskelinen from the University of Oulu, suggests that this may not be the case.
“Nutrient enrichment and loss of grazing are known to decrease diversity in aboveground plant communities. Seed banks are thought to maintain species’ populations in the soil even when they are declining or disappearing from aboveground communities and enhance the likelihood of community and ecosystem recovery”, says Eskelinen.
“However, we found that nutrient enrichment decreased diversity also in seed banks and made aboveground vegetation and seed banks more similar, which demonstrates that nutrient enrichment can weaken the potential for ecosystem resilience via seed banks, unlike previously thought. These results help explain why nutrient enrichment often has permanent negative effects on plant diversity that persist even after cessation of eutrophication”, Eskelinen continues.
“Another important result is that excluding grazers modified nutrient enrichment effects on seed banks, which highlights the importance of considering mammalian herbivores when assessing nutrient enrichment effects on seed banks”, says Lauren Sullivan, an associate professor from Michigan State University, USA, who led this project together with Eskelinen.
The international researcher team collected seed bank data from seven grasslands sites, spread on four different continents, and ranging from a tundra grassland in northern Finland to a semiarid grassland in Australia. These study sites are part of a global research cooperative Nutrient Network (NutNet), which consists of more than 130 grassland sites around the globe. The network addresses the effects of herbivores and different nutrients on grasslands which, while being important for wildlife, grazers, agriculture, and carbon sequestration, is a globally endangered ecosystem.
“These kind of global collaborative experiments are important because they allow generalizing community and ecosystem responses across a variety of climatic and environmental conditions, and with a different set of species. Our findings from seven sites around the world suggest that these effects are common and omnipresent”, says Risto Virtanen, a senior researcher at the Botanical Museum of Oulu University, who is also an author in this study and the principal investigator of the two Finnish NutNet sites together with Eskelinen.
“One of the practical implications of these results is that as species will be lost from the seed bank as a result of eutrophication, natural resilience of the ecosystem is lowered and recovery requires active restoration measures and supply of seeds by humans”, says Eskelinen.
Link to the publication: Eskelinen, A., Jessen, M.-T., Bahamonde, H.A., Bakker, J.D. Borer, E.T., Caldeira, M.C., Harpole, W.S., Jia, M., Lannes, L.S., Nogueira, C., Venterink, H.O., Peri, P.L., Porath-Krause, A.J., Seabloom, E.W., Schroeder, K., Tognetti, P.M., E. Yasui, S.-L, Virtanen, R., Sullivan, L.L. 2023. Herbivory and nutrients shape grassland soil seed banks. Nature Communications 14: 3949. Doi: https://doi.org/10.1038/s41467-023-39677-x