Participating Students - Rachel Vannette

Rachel Vannette 
University of Michigan
BART Enrollement Year: 2007
Email address: raleva at

Atmospheric Mentor: Mary Anne Carroll
Biospheric Mentor: Mark Hunter

Rachel Vannette is a 1st year graduate student in the University of Michigan’s Department of Ecology and Evolutionary Biology. She received her B.S. in Biology from Calvin College in Grand Rapids, MI before beginning graduate studies at U of M. She is interested in how mycorrhizal interactions affect terrestrial communities and ecosystem function. Rachel currently works with Dr. Mark Hunter on plant allocation trade-offs to growth, defense, and fungal symbionts under different resource gradients.

Research Topic:

AM Fungal Effects on Allocation Trade-offs in Asclepias syriaca Under Elevated CO2

Changing levels of atmospheric compounds will affect ecosystem function and nutrient cycling. Specifically, rising concentrations of CO2 and O3 affect carbon available for allocation to various demands within a plant. While CO2 increases photosynthetic rates and available photosynthate O3 damages photosynthetic tissue and decreases photosynthate available to plant demands. Plant defense against herbivores and AM fungal symbionts are two carbon sinks for a plant, and carbon allocation to these two demands carries different implications for community structure and population dynamics of the different trophic levels as well as carbon cycling and retention in soil and atmospheric pools.

This experiment will seek to measure allocation to two competing demands under elevated CO2 and O3 in Asclepias syriaca (common milkweed), a mycorrhizal prairie forb common throughout Michigan. Levels of cardenolides--defensive compounds found within the plant--and concentrations of AM fungi-specific lipids will be quantified to determine allocation to these demands.

 Elevated CO2 is predicted to increase allocation to both sinks, and potentially alleviate the trade-off between these two demands, while O3 is predicted to balance this effect and result in allocation similar to ambient conditions. If carbon allocation to AM fungi is increased, this flow of carbon to the soil will increase both respiration as well as increasing storage of carbon in soil organic pools.