• gametophytes;
  • gametogenesis;
  • Macrocystis;
  • irradiance;
  • quantum dose;
  • photoperiod;
  • Laminariales


Gametophytes of Macrocystis pyrifera (L.) C. Ag. were cultured under a series of quantum irradiances in three photoperiod regimes. The quantum irradiances in each photoperiod were adjusted to provide equal daily irradiation dosages between photoperiods which allowed a critical examination of the interactions between quantum irradiance and quantum dose in determining gametophyte fertility. The lowest quantum irradiance which stimulated gametogenesis in more than 50% of the female gametophytes was 5 μE·m−2·s−1. The saturating irradiance was ca. 10 μE·m−2·s−1 at photoperiods of 12 h or greater. In terms of daily quantum dose, the lowest dose at which greater than 50% gametogenesis occurred was 0.2 E·m−2·d−1. However, this critical quantum dose was higher (0.4 E·m−2·d−1) when instantaneous irradiances were less than 5 μE·m−2·s−1. The saturation quantum dose was also affected by the rate at which the quantum dose was received and varied from 0.4 to 0.8 E·m−2·d−1. Gametophytes in all three photoperiods reached 100% fertility at quantum irradiances above 5 μE·m−2·s−1. Photoperiod effects were small and could be accounted for by quantum dosage effects.