Floerkea proserpinacoides (Limnanthaceae) is a spring
ephemeral annual species that grows in deciduous
forests throughout eastern North America. Seeds germinate from late November
to December, although the first
leaf emerges only from late March to early April. Growth begins in early
April at the onset of favourable
temperatures, following snowmelt, and continues through mid-June. Senescence
coincides with increasing air
temperature and decreasing light level as a result of canopy closure. In
this paper, we present the results of a
growth chamber study designed to determine the effect of light level on
growth, biomass allocation and
reproduction of F. proserpinacoides. The study consists of two
parts: in a first experiment, plants were grown at
five constant photosynthetic photon fluence rates (PPFR: 90, 180, 360,
540 or 900 μmol m−2 s−1), and in a
second
experiment, PPFR was reduced from 900 μmol m−2 s−1
to 180 μmol m−2 s−1 after 0, 14, 21,
28 or 35 d of growth.
Relative humidity, temperature, nutrient and water supply were kept constant
in a hydroponic sand culture
experiment. Total biomass, leaf mass and leaf area increased with increasing
PPFR up to 540 μmol m−2 s−1. Plants
grown at the highest (900 μmol m−2 s−1)
and the lowest (90 μmol m−2 s−1) PPFR
had a substantially lower biomass
by the end of the 35-d growth period than plants grown at intermediate
PPFRs (360 or 540 μmol m−2 s−1). Despite
differences in total biomass, there were no significant differences in
seed production among treatments. The mean
relative growth rate (RGR) increased with increasing light levels between
90–540 μmol m−2 s−1, and it
was reduced
at 900 μmol m−2 s−1. However, differences
in RGR were not significant among treatments. Specific leaf area did not
vary consistently as a function of light level, whereas leaf area ratio
and leaf mass ratio tended to increase with
increasing PPFR, reaching maximum values at 360–540 μmol m−2
s−1. However, none of these growth variables
differed significantly across the range of PPFR levels. The transfer of
plants to lower PPFR had no significant
effect on any of the growth components. Biomass production for the species
appeared to be optimized at PPFR of
360–540 μmol m−2 s−1. Growth
might be restricted by an insufficient supply of photosynthates at low
PPFR and
by photoinhibitory processes at higher PPFRs.