I also investigated the potential for inherent genetic variation to affect vegetation response to global change. Such variation bears consequences for ecosystem productivity and evolutionary responses, and for extrapolating predictions based on experimental data, which necessarily document the dynamics of a limited number of individuals. To determine how levels of relatedness affect responses to CO2, I collected seeds from red maple (Acer rubrum) trees representing six populations and three provenances in North Carolina; this work is described in Mohan et al. (2004) published in Global Change Biology. I germinated these seeds and grew the resulting trees for two years under four CO2 levels: 180 μl/l, 270 μl/l, 360 μl/l, and 600 μl/l - representing Pleistocene, pre-Industrial Revolution, ambient, and potential future conditions. I found that all levels of relatedness interacted with CO2 to explain variation in plant response and that, in particular, red maple trees from different regions responded independently to CO2 enrichment. This suggests that species' responses to future atmospheric CO2 and the accompanying effects on forest composition will vary significantly among families, populations, and provenances.
By growing red maple trees under very different CO2 conditions, I produced foliar samples of widely varying qualities (i.e., [carbon:nitrogen] ratios). In a second phase of the above experiment, I asked whether genetic variation in foliage production and nutrient uptake would translate into intraspecific differences in CO2 effects on decomposition and nutrient turnover. I found a large degree of genetic variation in foliage production, plant uptake of nitrogen and phosphorus, and eventual tissue decomposition responses to atmospheric CO2. Due to lower [carbon:nitrogen] ratios and enhanced tissue quality, foliage produced under subambient CO2 conditions decomposed much more rapidly than that grown under present-day concentrations. This implies historical and paleo-rates of ecosystem nutrient turnover may have been faster than current rates would suggest. However, due to genetic variation in responses, future decomposition responses to increasing CO2 will vary even within mono-specific stands, and among same-species forests of different regions.