STOVER, DANIEL B.* and KEITH GARBUTT. West Virginia University, Department of Biology, Morgantown, WV 26506. - Fitness of clonal genotypes of Juncus effusus L. in differing nutrient regimes.
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