Light environment and pigment composition of Megaceros pellucidus

The hornwort Megaceros pellucidus occupies wet, heavily shaded sites. In four sites in thecentral North Island of New Zealand the maximum photon flux density (PFD) was always less than 10μmol m-2 s-1. The PFD varied weakly during the day depending exponentially on the PFD of full sunlight.Light reflected from surface water late in the day transiently doubled the mid-day maximum PFD.Sunflecks had little impact on the site PFD consistent with the exponential relationship between the PFDsmeasured at the site and canopy. Plants from low light conditions (0.2 μmol m-2 s-1) had the samecarotenoid content as plants from higher light conditions (6.9 μmol m-2 s-1), but the chlorophyll contentof high light plants was approximately twice that of low light plants. The chlorophyll a/b ratio was thesame for plants from low and high light conditions. Spectra of acetone-extracts of M. pellucidus thallusfrom low light grown plants showed an absorbance band at about 340 nm that was not apparent inspectra of extracts from plants grown in high light conditions.