Charophyte germination and establishment under low irradiance

Charophyte establishment from oospores in lake sediment was measured under nine light regimes (range <0.01-7.4 mol photons PAR m(-2) d(-1)) in two short-term experiments (13-20 weeks). Natural light was modified by inorganic turbidity in Experiment I and controlled artificial light was used in Experiment 2. Germling response was dominated by Chara australis Brown or Chara globularis Thuill. Germling number was not significantly affected by the light regimes and germination occurred under <0.5 mumol photons PAR m(-2) s(-1) ('Dark' treatment). A three-fold range in PAR (1.7-5.2 mol photons m(-2) d(-1)) had less influence on the final germling number than pre-drying sediment, which increased germlings ca. 1.5- to 3-fold. Drying lake sediment could be used as a management tool to stimulate charophyte germination. Light influenced germling biomass, with negligible gain at less than or equal to0.4 mol photons PAR m(-2) d(-1) and biomass accrual with light greater than or equal to 1.7 mol photons PAR m(-2) d(-1). Germination at an irradiance insufficient to sustain germling growth suggests that this may be an important loss for oospore banks under unfavourable light conditions and might be an adaptation to germination within the soil profile. The results of these experiments indicate that for these species, light is required for establishment rather than germination. (C) 2004 Elsevier B.V. All rights reserved.