The cycling of nutrients such as nitrogen through ecosystems is a critical process that maintains biodiversity and environmental services of agricultural, urban, and natural lands. There is increasing evidence that the way plant and animal species interact with each other could control the rate of nutrient cycling. For instance, many plants respond to herbivore damage by producing defensive anti-herbivore chemicals in their tissues to ward off further damage. These defensive compounds could also slow down the nitrogen cycling rate when dead plant material enters the soil by impairing microbial decomposition. Understanding how the soil nutrient environment changes plant growth and the production of plant defenses is of critical importance to agronomists interested in lowering pesticide and fertilizer use while maximizing yield. Results of the study will be communicated to local stakeholders and small-scale farmers near the study site through a workshop and seminar designed to integrate knowledge of ecosystem dynamics into sustainable land management strategies. In addition, continuing engagement with a local township conservation commission will incorporate study results directly into land management strategies. Results will be shared through presentations at professional meetings and funding will support the mentoring of undergraduates on projects with the potential for co-authorship on publications that arise from the work.
Linking genes to ecosystem function is a recent focus in ecosystem ecology, because a plant's genotype determines how it functions and thus has the potential to impact ecosystem processes. Plant genotypes are also shaped by their growing environment, however, resulting in differential trait expression across environmental conditions. Knowing how such trait plasticity connects to ecosystem functioning is fundamental to prediction of how environmental change will influence ecosystem processes like nitrogen (N) cycling. Interactions among rates of herbivory, structural anti-herbivore defensive compounds, and site fertility can all affect trait plasticity and thus can affect the connections between genes and ecosystems. These interactions will be examined manipulating the growing environment in caged raised bed garden plantings of several different genotypes of a common meadow plant, goldenrod (Solidago altissima), which innately express anti-herbivore defenses differently under different conditions. The experiment will exclude or add Melanoplus femurrubrum grasshopper herbivores and exclude or add fertilizer. The study will measure how rapidly soil microbes decompose plant leaf litter from the genotypes grown in the different herbivory and fertilizer conditions. Subsequent experiments will measure how this processing changes soil microbial communities, soil nitrogen availability, and subsequent plant growth and traits. Finally, a 15N tracer experiment will allow measurement of nitrogen cycling by tracking the amount of nitrogen in the soil and in plants after it is released by microbial decomposition. Taken together these experiments will determine whether plant genotype, the expression of plant anti-herbivore traits, or soil N level best predicts N cycling within ecosystems.
