Burial limits to the emergence of aquatic plant propagules

Abstract

The sediment depth limits to germling emergence were determined for five common New Zealand submerged plants. A significant trend was observed of declining emergence with increasing burial depth. Emergence from small oospores (13-16 μg) of Nitella pseudoflabellata A. Br. and Nitella leptostachys A. Br. was limited to the surface sediment (<25 mm). Potamogeton ochreatus Raoul seed (1460 μg) emerged from <50 mm depth. Chara corallina Willd. oospores (148 μg) emerged from burial depths of at least 50-75 mm, while Chara globularis Thuill. oospores (50 μg) were able to emerge from the maximum tested depth of 100 mm. The observation that burial limits to emergence by Chara species were at least twice that of the much larger P. ochreatus seed is at odds with theory that the size of propagule reserves act to determine emergence ability. However, it is in keeping with suggested energy efficiency of shoot extension in the macroalgae versus vascular species. Results indicate that assessment of submerged seed banks should concentrate on the upper 50 mm of sediment which contains most "ecologically active" propagules.