Nutrient enrichment alters seasonal beta-diversity in global grasslands

Authors: GARBOWSKI, MAGDA - German Centre For Integrative Biodiversity Research (IDIV); BOUGHTON, ELIZABETH - Archbold Biological Station; EBELING, ANNE - University Of Jena; FAY, PHILIP - Retired ARS Employee; HAUTIER, YANN - Utrecht University; HOLZ, HANNA - Martin Luther University; JENTSCH, ANKE - University Of Bayreuth; JURBURG, STEPHANIE - Helmholtz Centre For Environmental Research; LADOUCEUR, EMMA - University Of Leipzig; MARTINA, JASON - Texas State University; OHLERT, TIMOTHY - Colorado State University; RAYNAUD, XAVIER - The Sorbonne University; ROSCHER, CHRISTIANE - Helmholtz Centre For Environmental Research; SONNIER, GREGORY - Archbold Biological Station; TOGNETTI, PEDRO - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); YAHDJIAN, LAURA - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); WILFAHRT, PETER - University Of Minnesota; HARPOLE, STAN - Martin Luther University

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2023
Publication Date: 8/21/2023
Citation: Garbowski, M., Boughton, E., Ebeling, A., Fay, P., Hautier, Y., Holz, H., Jentsch, A., Jurburg, S., Ladouceur, E., Martina, J., Ohlert, T., Raynaud, X., Roscher, C., Sonnier, G., Tognetti, P.M., Yahdjian, L., Wilfahrt, P., Harpole, S. 2023. Nutrient enrichment alters seasonal beta-diversity in global grasslands. Ecology. 111(10):2134-2145. https://doi.org/10.1111/1365-2745.14182.
DOI: https://doi.org/10.1111/1365-2745.14182

Interpretive Summary: Native grasslands provide numerous ecosystem services including food, fuel, and fiber. Provision of ecosystem services depends in part on the presence of many plant species which grow at different times of the growing season. The characteristics of species at different times of the season may influence their response to global change drivers such as eutrophication, which is an excess of nutrients in the environment. Temporal separation of species is predicted to be highest in grasslands with strong seasonal climate variability. Most experimental tests of this prediction have been conducted at single locations and the generality of this prediction across multiple locations at a global scale has not been explored. ARS scientists and university collaborators measured the presence and abundance of early- and late-season plant species from 10 grassland sites around the world and explored relationships between within-season precipitation and temperature variability, nutrient enrichment, and the degree to which different plant species occurred early or late in the growing season (seasonal beta-diversity). Higher within-season temperature variability and nutrient enrichment, but not precipitation variability, correlated with increased seasonal beta-diversity, reflecting increased difference in which species were present early vs. late in these communities. Specific categories of plant species, C4 graminoids and legumes were strongly reduced in abundance by nutrient enrichment, while C3 graminoid and annual forb species increased and C3 graminoids became strongly seasonal. These findings demonstrate the generality of seasonal species changes in grasslands, highlight an important relationship between intra-annual temperature variability and seasonal species change, and identify an important role for nutrient enrichment in seasonal changes in grasslands plant communities. These changes likely alter ecosystem services provision in grasslands.

Technical Abstract: In many grasslands, species with specific traits occupy unique temporal positions within communities. Such intra-annual, or seasonal, segregation is predicted to be highest in systems with high intra-annual climate variability because fluctuating environmental conditions provide opportunities for temporal niche partitioning among species. However, because evidence for these patterns has been gathered at individual sites, relationships between intra-annual climate variability and seasonal dynamics at global scales have not been explored. Further, the same characteristics that promote species-specific responses to environmental fluctuations may influence species-specific responses to global change drivers such as eutrophication. Research provides evidence of eutrophication effects at inter-annual scales, yet understanding of how it alters intra-annual dynamics remains limited. We used early- and late-season compositional data collected from 10 grassland sites around the world to explore relationships between intra-annual precipitation variability and temperature variability and intra-annual species segregation (i.e., seasonal beta-diversity) and to assess how nutrient enrichment alters seasonal beta-diversity in plant communities. We then assessed whether changes in seasonal beta-diversity in response to eutrophication are underpinned by species turnover or nestedness and determined how specific functional groups (i.e., annual forbs, perennial forbs, C3 and C4 graminoids, and legumes) respond to treatments within and across early and late sampling dates. We found a positive relationship between intra-annual temperature variability and seasonal beta-diversity but observed no relationship between intra-annual precipitation variability and seasonal beta-diversity. We found that nutrient enrichment increased seasonal beta-diversity via increased turnover of species between early- and late-season communities. This finding mirrors patterns observed at inter-annual scales and suggests fertilization can alter compositional dynamics via similar mechanisms at varied temporal scales. Fertilization reduced the abundance of C4 graminoids and legumes within and across seasons and eliminated intra-annual differences in these groups. In contrast, fertilization resulted in intra-annual differences in C3 graminoids which were not observed in control conditions, and increased abundance of C3 graminoids and annual forbs overall. Our study demonstrates a positive relationship between intra-annual temperature variability and seasonal beta-diversity and highlights how nutrient enrichment alters seasonal community dynamics in grasslands.