SEED-GERMINATION RESPONSES TO SOME ENVIRONMENTAL-FACTORS IN THE SEAGRASS ZOSTERA-CAPRICORNI FROM EASTERN AUSTRALIA

The germination requirements of Zostera capricorni Aschers. were studi ed in relation to temperature, salinity and oxygen potential. In treat ments maintained at 16 degrees C (corresponding to winter mean water t emperature) and a salinity of 15 parts per thousand (half that of norm al seawater), the cumulative percentage germination in both aerobic an d anaerobic treatments was over 80%. However, seed germination was muc h faster under anaerobic conditions than aerobic conditions (cf mean t ime-to-germinate (MTG) of <41 and >136 days, respectively). Under anae robic conditions, at a constant 16 degrees C, salinity level did not a ffect germination which was high (>80%) and rapid (MTG<41 days) at bot h 15 parts per thousand and 30 parts per thousand. However, under aero bic conditions, percentage germination did not exceed 60% at the highe r salinity, 30 parts per thousand, at the end of the experiment. Germi nation was also slower at the higher salinity, 30 parts per thousand, compared to 15 parts per thousand (MTG=159.6 and 136.3 days, respectiv ely) but in both cases this was considerably slower than that recorded under anaerobic conditions. In all treatments held at 26 degrees C (c orresponding to summer mean water temperature) the MTG of seeds was hi gh (>82 days) and the cumulative percentage germination did not exceed 40%. The effects of temperature on germination were more marked under anaerobic conditions than aerobic conditions. When Z. capricorni seed s were transferred to 16 degrees C, after 24 days at 26 degrees C (whe re germination rate was very slow), rapid germination followed in the anaerobic treatments. In contrast, when seeds were similarly transferr ed from 16 degrees C to 26 degrees C, the germination rate decreased t o a negligible level following a 1-week lag period immediately after t ransfer when they continued to germinate rapidly. After 5 months cold stratification in artificial seawater at 6 degrees C, both final germi nation and germination rate under anaerobic conditions were broadly si milar to that recorded in unstratified seeds. In contrast, under aerob ic conditions despite the fact that final germination at both salinity levels did not exceed 60%, stratified seeds germinated much quicker t han unstratified seeds (average MTG value across both salinity levels, 51.2 and 148 days, respectively) indicating a reduction in the condit ional dormancy originally maintained by aerobic conditions. (C) 1998 E lsevier Science B.V. All rights reserved.