Dissertation Research: Differential Stress Tolerance in Dioecious Plants

过去，植物学家认为，在不同的植物上分离雄花和雌花(雌雄异株)可能阻止了自花受精和与持续近亲繁殖相关的固有问题。然而，最近，关于雌雄异株的进化和维持的其他建议也被提出。这些假设中有几个是基于男性和女性生殖成本的差异。雌性被认为有更高的生殖成本，因为她们为种子和果实的发育提供能量、水和营养。相比之下，男性只经历了生产受精用花粉的成本。由于生殖成本的这种差异，人们假设雌性在低资源条件下会经历更大的压力，如遮荫、低营养可获得性和低水分状况，因此在不利的生态地点出现的频率较低。这一预测在许多描述性研究中得到了定性的证实，这些研究表明，在某些物种中，雄性和雌性在空间上是沿着生态压力梯度分开的。然而，雄株和雌株在胁迫耐受性方面的差异只在三个物种中进行了实验研究，结果尚不确定。本项目将重点研究几种雌雄异株植物在光、水和氮素利用率较低的条件下的抗逆性差异。为了衡量植物的耐逆性水平，我们将测量植物生长和光合作用速率对胁迫处理的响应。将使用三个雌雄异株物种的个体，Thalictrum dasycarpum，Silene Alba和Spinacia Holacea。将监测个体在每个物种内的光合作用速率和生长模式的差异。还将测量叶片的水分和氮含量。

In the past, botanists have reasoned that the separation of the male and female flowers on different plants (dioecy) may have prevented self-fertilization and the inherent problems associated with continuous inbreeding. Recently, however, other suggestions concerning the evolution and maintenance of dioecy have been proposed. Several of these hypotheses are based on the differential costs of reproduction in males and females. Females are hypothesized to have higher reproductive costs because they supply the energy, and water, and nutrients for seed and fruit development. Males, in contrast, only experience the costs of producing pollen for fertilization. Because of this difference in reproductive costs, it has been assumed that females would experience greater stress under low resource conditions such as shading, low nutrient availability and low water situations and would therefore be found with less frequency in unfavorable ecological sites. This prediction has been borne out qualitatively in many descriptive studies which have indicated that in some species males and females are spatially segregated along ecological stress gradients. However, differences between male and female plants in degree of stress tolerance has been experimentally studied in only three species and results have been inconclusive. This project will focus on differences in stress tolerance between male and female plants of several dioecious species under conditions of low availability of light, water and nitrogen. In order to gauge the level of stress tolerance the response of plant growth and photosynthesis rate to the stress treatments will be measured. Individuals of three dioecious species, Thalictrum dasycarpum, Silene alba, and Spinacia oleracea, will be used. Individuals will be monitored for differences in photosynthetic rates and growth patterns within each species. Water and nitrogen contents of leaves will also be measured.