Effects of Nitrogen Addition Timing and Herbivory on Plant Diversity
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Different factors such as nutrient addition or herbivore loss are known to decrease plant species richness in tallgrass prairies. However, little is known about how variation in timing affects these factors. For example, an intense, brief addition of nitrogen (N) could have a greater effect on species richness versus persistent, low levels of N addition because of the community’s prolonged exposure to N. Furthermore, herbivore activity may reverse the effects of N temporal variation by balancing out the differences. The purpose of this project was to determine if adding a set amount of N to soil over different timeframes would change species richness with herbivory. To accomplish this, we added a constant amount of N to pots containing six tallgrass prairie plant species, in different temporal regimes. Half received all of the N pulse in the beginning of the experiment, while the other half received the same amount in weekly doses over four weeks. We measured percentage cover before and after simulated herbivory. Final biomass was also collected at the end of the experiment by cutting plants at the soil surface. We expect that the addition of N in the absence of herbivory will decrease plant species richness when compared to the N treatment with herbivory. We also expect that quick, intense levels of N will cause species richness to decline faster compared to smaller, persistent levels of N. This research addresses factors that possibly alter plant diversity in tallgrass prairie ecosystems.