Aber Krischik V, Denno R F
Center for Agricultural Biotechnology, University of Maryland, 20742, MD, College Park, USA.
Oecologia. 1990 Jun;83(2):176-81. doi: 10.1007/BF00317749.
Baccharis halimifolia (Compositae) is a dioecious shrub which grows on the upland fringe of tidal marshes along the Atlantic and Gulf Coasts of North America. We examined the responses of the two sexes to variation in nutrient and moisture availability plant density, and defoliation. By growing plants from seedlings to flowering adults under various combinations of soil type, fertilization rate and plant density, we were able to establish different rates of plant growth and mortality. Plants grown at high density and low nutrient and water supply grew the least, incurrent the most mortality and showed a male-biased sex ratio (73% male). At low density with abundant nutrients and water, plants grew more, survived well, flowered frequently, and were female-biased (75% female). Changes in sex ratio were probably the result of sex-related mortality rather than sexual lability of the seedlings. While changes in sex ratio occurred under experimental conditions in the green-house, no evidence for differences in habitat utilization between the sexes were found in the field and the sex ratio (59% female) did not vary across habitats. In the marsh habitats we sampled where water and nutrients were apparently available, there was no evidence for differential mortality between the sexes. When defoliated (75% of leaf tissue), both sexes showed similar reductions in reproductive effort (number of flower heads/shoot). Our results indicate that differences between the sexes of Baccharis in their response to environmental growing conditions is an important ecological factor associated with the separation of male and female function into separate individuals.
海滨兔树（菊科）是一种雌雄异株的灌木，生长在北美大西洋和墨西哥湾沿岸潮汐沼泽的高地边缘。我们研究了两性对养分、水分可利用性、植株密度和去叶处理变化的反应。通过在不同土壤类型、施肥率和植株密度组合下将幼苗培育至开花成年植株，我们得以确定不同的植株生长率和死亡率。在高密度以及低养分和低水分供应条件下生长的植株生长最慢，死亡率最高，且呈现雄性偏多的性别比例（73%为雄性）。在低密度且养分和水分充足的条件下，植株生长更多，存活率高，频繁开花，且雌性偏多（75%为雌性）。性别比例的变化可能是与性别相关的死亡率导致的，而非幼苗的性可塑性。虽然在温室实验条件下出现了性别比例的变化，但在野外未发现两性在栖息地利用上存在差异的证据，且性别比例（59%为雌性）在不同栖息地之间没有变化。在我们采样的沼泽栖息地中，水和养分显然是可获取的，没有证据表明两性之间存在差异死亡率。当进行去叶处理（去除75%的叶片组织）时，两性的繁殖投入（头状花序数/枝条）都出现了类似程度的降低。我们的结果表明，海滨兔树两性对环境生长条件的反应差异是一个重要的生态因素，与雄性和雌性功能分离到不同个体有关。
