Effects Of Nitrogen And Nutrient Co-Limitation On Carbon Dynamics And Plant Community Composition

Abstract

Despite its necessity in all life forms, nitrogen (N) is a limiting nutrient in many ecosystems. However, N availability is increasing through human-derived inputs, in particular through deposition of reactive N as a result of fossil fuel emissions and fertilizer volatilization. Anthropogenic N deposition currently represents a relatively small, but continuous, addition of N into ecosystems; but, because N is frequently limiting to plant growth, particularly in terrestrial systems, this small flux can have substantial effects on ecosystem diversity, productivity, and function. Grasslands, covering 40% of Earth’s land surface, are a particularly important biome in which to study the effects of N deposition because of their high biodiversity as well as agricultural and environmental value. In my dissertation, I studied how small rate of N inputs, similar to rates of N deposition, affect plant community composition, productivity, and carbon fluxes. I also investigated how the effects of N were contingent on the supply of other commonly limiting nutrients, such as phosphorus (P), potassium (K), and micronutrients (µ). I found consistent nonlinear responses to N addition, with plant biomass and carbon fluxes peaking at low rates of N addition. Additionally, I found that the effects of high rates of N were contingent on the supply of PKµ, and that plant community composition only changed when all three nutrients were added together. Overall, my work indicates that plant community response to nitrogen is dependent on both rate of N supply and supply of nutrients other than N.