Sullivan Gary, Titus John E
Department of Biological Sciences, Binghamton University, 13902-6000, Binghamton, NY, USA.
Pacific Estuarine Research Laboratory, San Diego State University, 92182-4625, San Diego, CA, USA.
Oecologia. 1996 Oct;108(2):285-292. doi: 10.1007/BF00334653.
Experimental and observational studies of the submersed, freshwater macrophyte Vallisneria americana Michx. revealed that depth, wind and wave exposure, and current velocity may all influence fruit set. In this dioecious species, long-pedunculate female flowers are pollinated by free-floating male flowers at the water surface. Average fruit set in the natural populations studied varied from zero to 97% of the flowers observed. With increasing water depth in New York and Pennsylvania lakes, female plants continued to flower, though these flowers were unable to reach the surface, and consequently, did not set fruit. Fruit set was also lower in relatively open sites exposed to wind and waves, presumably because male flowers do not remain in the vicinity of female flowers long enough for effective pollination. This was particularly striking at a site with low male flower densities, but fruit set was increased to 100% at that site by confining the floating male flowers within a field enclosure. In a river, fruit set was negatively correlated with surface current velocity, and was reduced to zero in current velocities greater than 0.30 m · s. Fruit set in V. americana appears to be restricted or precluded by physical environmental conditions in a variety of sites.
对沉水淡水大型植物美洲苦草（Vallisneria americana Michx.）的实验研究和观察研究表明，深度、风浪暴露情况以及水流速度都可能影响结果率。在这种雌雄异株的物种中，长梗雌花由水面上自由漂浮的雄花授粉。在所研究的自然种群中，观察到的花朵平均结果率从零到97%不等。在纽约和宾夕法尼亚州的湖泊中，随着水深增加，雌株继续开花，但这些花朵无法到达水面，因此无法结果。在相对开阔、暴露于风浪的地点，结果率也较低，可能是因为雄花在雌花附近停留的时间不够长，无法进行有效授粉。在一个雄花密度较低的地点，这种情况尤为明显，但通过将漂浮的雄花限制在田间围栏内，该地点的结果率提高到了100%。在一条河流中，结果率与表面水流速度呈负相关，当水流速度大于0.30米·秒时，结果率降至零。在各种地点，美洲苦草的结果率似乎受到物理环境条件的限制或阻碍。
