The effect of light on the growth and reproduction of Floerkea proserpinacoides

Abstract

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 −# s −" ), and in a second experiment, PPFR was reduced from 900 µmol m −# s −" to 180 µmol m −# s −" 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 −# s −" . Plants grown at the highest (900 µmol m −# s −" ) and the lowest (90 µmol m −# s −" ) 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 −# s −" ). 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 −# s −" , and it was reduced at 900 µmol m −# s −" . 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 −# s −" . 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 −# s −" . Growth might be restricted by an insufficient supply of photosynthates at low PPFR and by photoinhibitory processes at higher PPFRs.

Why are annual plants rarely spring ephemerals?

“…There was an overall increase in SLA and LMR in response to shading (Table 1 ; P l 0n0001 and P l 0n0002, respectively, for the factor ' light '). In agreement with our earlier study (McKenna & Houle, 1999), F. proserpinacoides was able to adjust some of its leaf traits to enhance light capture under shaded conditions, yet this plastic response appeared to be limited relative to the responses reported for other light-demanding species (Morgan & Smith, 1979 ;Dudley & Schmitt, 1995 ;Hunt & Cornelissen, 1997). Floerkea proserpinacoides plants also showed marked stem elongation when partially shaded, and this was associated with an overall greater SMR (Table 1 ; P l 0n0121 for the factor ' light ').…”

“…Although F. proserpinacoides is recognized as a heliophyte (Gauthier & Rousseau, 1973 ;Smith, 1983), we showed previously that these plants could grow and reproduce successfully across a range of PPFDs from 90 to 900 µmol m −# s −" , at cool temperatures (16\7mC), and when nutrients and water were not limiting (McKenna & Houle, 1999). However, intermediate PPFD of c. 400 µmol m −# s −" was optimal for growth, and higher (900 µmol m −# s −" ) or lower (90 µmol m −# s −" ) PPFDs tended to reduce performance.…”

“…PPFD was measured with a portable photometer (model 189, Li-Cor, Inc., Lincoln, NE, USA) at the beginning of the experiment : values ranged from 433-454 (high), 182-196 (intermediate), and 85-100 (low) µmol m −# s −" at seedling height. These PPFDs were chosen in reference to a previous experiment where 360-540 µmol m −# s −" appeared optimal for growth (McKenna & Houle, 1999).…”

Effects of Light on the Growth and Clonal Reproduction of Ligularia virgaurea

“…Light is one of the most important environmental factors influencing growth and reproduction of plant species (Stuefer and Huber 1998; Mckenna and Houle 1999; Li et al 2001; Aleric and Kirkman 2005). Changes in the availability of light are likely to create strong selection pressures (Schmitt and Wulff 1993; Dong 1995; Chu et al 2006).…”

Potential distribution of three types of ephemeral plants under climate changes

“…They are primarily perennials that usually complete their life history in early spring before the tree canopy cover. Their life cycle was also concise; within 2 months, they can complete the aboveground (including fruit production) growth, and then they senesce and enter dormancy with underground organs, but the dormancy was not very deep ( Mckenna & Houle, 1999 ). Differentiation can occur in the bud of the underground organ during summer.…”