Nutrient enrichment and herbivore loss are thought to cause a loss of plant diversity in grassland ecosystems because they increase plant cover, which reduces light in the understory. Plants require light to grow. However, less light can reach lower vegetation layers in grasslands due to excess nutrients and/or the absence of herbivores. As a result, a few fast-growing species predominate, and plant diversity decreases. So far, this relationship has been established indirectly through experiments, but never directly through the addition of light to the field. Now, biologists have been able to demonstrate the dominance of light competition experimentally.
For their experiments, the team of researchers led by Prof. Dr. Anu Eskelinen from the University of Oulu (Finland) used the Global Change Experimental Facility (GCEF) at the UFZ research station in Bad Lauchstädt. Scientists from UFZ, iDiv, and other universities use the GCEF platform to investigate the impact of different climate models and land use intensities on plant community structure, specifically food webs and species interactions.
Anu Eskelinen, a visiting scientist at UFZ and iDiv for several years, used a novel experimental approach: the team directly illuminated the low-growing plants in the grassland with LED lamps, increasing the amount of light. In addition to this treatment, fertilizers were applied to some plots and sheep grazing was used on others.
The research team believes that the results from the field trials should be taken into account for future grassland management and conservation policies. Our results highlight the importance of conserving native herbivores and using sustainable grazing as a management measure.
Anu Eskelinen
The experiment showed a sharp decline in species richness and biodiversity as a result of artificial fertilization if the areas were not grazed at the same time. When the researchers added LED lamps, the loss of species richness was mitigated. Later, the researchers excluded sheep from half of the plots, which caused species richness and diversity do decline.
At the same time, the total vegetation cover increased without grazing, which, in turn, reduced the light available to plants. Importantly, adding light to the understorey plants mitigated this loss of diversity. “These results suggest that herbivory is a dominant factor controlling competition for light and plant diversity,” says first author Anu Eskelinen.
The research team believes that the results from the field trials should be taken into account for future grassland management and conservation policies. “Our results highlight the importance of conserving native herbivores and using sustainable grazing as a management measure,” Anu Eskelinen further emphasises.
Prof. Dr. Stan Harpole, co-author, and head of the department of Physiological Diversity at UFZ and iDiv, adds: “This study highlights the value of carefully designed manipulative field experiments, which we need so we can strongly test the causes of diversity loss. We could only advance our understanding and test the theory in more realistic conditions because of the excellent infrastructure of the UFZ’s Global Change Experimental Facility and the support provided at the Bad Lauchstädt Research Station, and the cooperation with iDiv.”
