Document: BRY-3-64-19

Effects of soil nutrient depletion and enrichment on plant biodiversity and restoration in a Kansas grassland.

SCHRAG, A.M.*, V.H.SMITH, B.L.FOSTER and V.L.PETERSON

University of Kansas, Lawrence, KS 66045 USA ¹

Abstract:
An experimental nutrient gradient was established in 1996 in a disturbed grassland at the Nelson Environmental Studies Area of the University of Kansas to investigate the effects of soil nitrogen depletion, and nitrogen and phosphorus enrichment on plant biodiversity and restoration. The experimental design consists of fifty-four, 4 x 4 m plots, made up of six replicates of nine levels of N manipulation. The N treatments included seven nitrogen enrichment treatments (0 g m^-2 yr^-1; 1 g m^-2 yr^-1; 2 g m^-2 yr^-1; 3.4 g m^-2 yr^-1; 5.4 g m^-2 yr^-1; 7.5 g m^-2 yr^-1; 9 g m^-2 yr^-1) and two N depletion treatments (achieved through sawdust additions: 31 g m^-2 yr^-1; 62 g m^-2 yr^-1). At the beginning of the experiment, seeds of several native prairie species, including four native C₄ grasses, were added to the plots. In the second year of the experiment, three replicates of each N treatment were enriched with phosphorus (in a sufficient amount to double ambient soil P levels), yielding a 2 by 7 factorial N and P gradient. In response to N enrichment, plant biomass has increased in most years, and species diversity has declined. By year 4, native grasses became dominant in the sawdust and control treatments, but declined in abundance with increasing rates of N addition as the abundance of introduced annual grasses increased. The results are in agreement with several other fertilization studies and confirm that N pollution is a threat to plant biodiversity and to our capacity to restore degraded grasslands back to native species.

Keywords: Diversity, grassland, native grasses, nitrogen depletion, nitrogen enrichment, restoration

This abstract is being presented at: 10:30 AM in session:
RESTORATION ECOLOGY AND INVASIONS