James Broda, Ph.D

Title: Nitrogen, Litter, and Biodiversity Loss in North American Grasslands

Abstract. While perhaps less discussed than the carbon cycle, the nitrogen cycle is no less essential to the health of terrestrial ecosystems. In particular, excess nitrogen from agricultural runoff and fossil fuel emissions has caused biodiversity to decline in North American grasslands by disrupting the balance of resource competition among different species. On the bright side, recent efforts to reduce fossil-fuel emissions and to modify agricultural practices have led to localized decreases in nitrogen deposition. This raises the question of whether or not the biodiversity losses are reversible, for which empirical evidence is mixed. Hypothesized mechanisms preventing recovery of biodiversity include nutrient recycling, insufficient external seed supply, and litter inhibition of plant growth. In this talk, I will present a model that unifies these mechanisms and qualitatively matches observations from a long-term N-enrichment study in Minnesota.