It has been hypothesized that there is a genetic tradeoff between resource use efficiency (RUE) and resource acquisition rate (RAR) in that it is not possible for selection to maximize both these traits. In low resource environments RUE is expected to be favored while in high resource environments RAR will be maximized. In this study we examine this hypothesis using Juncus effusus L. clones from sites with high and low nitrogen availability. Ten genotypes of J. effusus were removed from each of four field sites differing in nitrogen availability (two high and two low). Theses were hydroponically cloned and then were reciprocally transplanted back into the field sites. Tiller number, length, time of reproduction and death was measured biweekly. Plant growth was assessed by determining the relative (tiller/tiller/day) and absolute growth rates (tillers/day). Preliminary results show a direct correlation between site nutrient level and growth rates. Genotypes from high nitrogen sites had the lowest efficiencies when transplanted into low nitrogen field sites. In low nitrogen environments, native genotypes consistently had higher growth rates than high nitrogen genotypes. Conversely, the highest growth rate for high nitrogen clones was observed within their home field sites. This inverse interaction between genotypes and nitrogen status implies that a home site advantage has been developed. Clones from high nutrient sites appear to exhibit higher RAR to adapt to the higher relative abundance of nitrogen. In conclusion, our preliminary trends show an inherent divergence in the growth responses of J. effusus to site nitrogen availability. This divergence may represent genetic tradeoffs between RAR and RUE and overall inability to maximize both these traits in opposing nitrogen environments.

Key words: absolute growth rate, Juncus effusus, relative growth rate, resource acquisition rate, resource use efficiency