Nutrient addition shifts plant community composition towards earlier flowering species in some prairie ecoregions in the U.S. Central Plains

Authors: BIEDERMAN, LORI - Iowa State University; MORTENSEN, BRENT - Iowa State University; Fay, Philip; HAGENAH, NICOLE - University Of Kwazulu-Natal; KNOPS, JOHANNES - University Of Nebraska; LA PIERRE, KIMBERLY - University Of California; LAUNGANI, RAMESH - Doane University; LIND, ERIC - University Of Minnesota; MCCULLEY, REBECCA - University Of Kentucky; POWER, SALLY - Western Sydney University; TOGNETTI, PEDRO - Universidad De Buenos Aires

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2017
Publication Date: 5/26/2017
Publication URL: http://handle.nal.usda.gov/10113/5852152
Citation: Biederman, L., Mortensen, B., Fay, P.A., Hagenah, N., Knops, J.M., La Pierre, K.J., Laungani, R., Lind, E.M., McCulley, R.L., Power, S., Tognetti, P. 2017. Nutrient addition shifts plant community composition towards earlier flowering species in some prairie ecoregions in the U.S. Central Plains. PLoS One. 12(5):e0178440. https://doi.org/10.1371/journal.pone.0178440.

Interpretive Summary: Many grasslands have been degraded by deposition of nitrogen in rainfall and particulates, a result in part of nitrogen loss from agriculture and industrial processes. Grasslands have also been degraded by the encroachment of non-native invasive species. In combination with ongoing warming caused by accumulating greenhouse gases in the atmosphere, these factors can shift the timing of flowering in grassland communities, with uncertain consequences for pollinators, beneficial organisms for agricultural and biological productivity and yield. This study examined shifts in the timing of community flowering in grassland to which nitrogen was experimentally added at 11 grasslands in the North American Central Plains. Nitrogen addition shifted community flowering earlier in tallgrass prairie sites, but not in other grassland forms. This may disconnect beneficial pollinator populations from their food source, potentially reducing populations of these species that pollinate many agricultural crops.

Technical Abstract: The distribution of flowering across the growing season is governed by each species’ evolutionary history and climatic variability. However, global change factors, such as eutrophication and exotic species invasion, can alter plant community composition and thus change flowering distribution. We examined three ecoregions (tall-, mixed, and short-grass prairie) across the U.S. Central Plains to determine how nutrient (nitrogen (N), phosphorus, and potassium (+micronutrient)) addition alters the temporal patterns of plant flowering traits. We calculated total community flowering potential (FP) by distributing peak-season plant cover values across the growing season by allocating each species’ cover value to only those months in which it typically flowers. We also generated separate FP profiles for exotic and native species and plant functional group. Only N altered the distribution of FP profiles (total and sub-groups) across the growing season. In all ecoregions, N increased the relative cover of both exotic species and C3 graminoids that flower early in the season. The cover of C4 graminoids decreased with added nitrogen, but the response in each ecoregion varied by month. However, these functional changes only shifted the FP profile of the entire community to earlier in the season for only the tall-grass prairie ecoregion. This pattern suggests that N-addition can shift the distribution of flowering activity by increasing the abundance of species that flower in sparsely occupied temporal niches. There was no change in the FP profile of the mixed and short-grass prairies with N addition as increased abundance of exotic species and C3 graminoids replaced other species that flower at the same time. In these latter communities a disturbance other than nutrient addition may be required to disrupt phenological patterns.