Seed germination responses to some environmental factors in the seagrass Zostera capricorni from eastern Australia

Abstract

The germination requirements of Zostera capricorni Aschers. were studied in relation to temperature, salinity and oxygen potential. In treatments maintained at 16°C (corresponding to winter mean water temperature) and a salinity of 15‰ (half that of normal seawater), the cumulative percentage germination in both aerobic and anaerobic treatments was over 80%. However, seed germination was much faster under anaerobic conditions than aerobic conditions (cf. mean time-to-germinate (MTG) of <41 and >136 days, respectively). Under anaerobic conditions, at a constant 16°C, salinity level did not affect germination which was high (>80%) and rapid (MTG<41 days) at both 15‰ and 30‰. However, under aerobic conditions, percentage germination did not exceed 60% at the higher salinity, 30‰, at the end of the experiment. Germination was also slower at the higher salinity, 30‰, compared to 15‰ (MTG=159.6 and 136.3 days, respectively) but in both cases this was considerably slower than that recorded under anaerobic conditions. In all treatments held at 26°C (corresponding to summer mean water temperature) the MTG of seeds was high (>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 seeds were transferred to 16°C, after 24 days at 26°C (where germination rate was very slow), rapid germination followed in the anaerobic treatments. In contrast, when seeds were similarly transferred from 16°C to 26°C, the germination rate decreased to a negligible level following a 1-week lag period immediately after transfer when they continued to germinate rapidly. After 5 months cold stratification in artificial seawater at 6°C, both final germination and germination rate under anaerobic conditions were broadly similar to that recorded in unstratified seeds. In contrast, under aerobic conditions despite the fact that final germination at both salinity levels did not exceed 60%, stratified seeds germinated much quicker than unstratified seeds (average MTG value across both salinity levels, 51.2 and 148 days, respectively) indicating a reduction in the conditional dormancy originally maintained by aerobic conditions.