Desert soils are coated with living microscopic organisms, known as the "crust", with mosses among the most conspicuous of these organisms. This crust performs several valuable ecological functions that ensure the continued overall health of the plant and animal community. The principal moss in the Mojave Desert ecosystem is characterized by very low levels of sexual reproduction due to male rarity, and given the importance of this moss to the long term health of the desert ecosystem, the aim of this study is to determine why sexual reproduction and males are so rare. The hypothesis guiding the research is that rare males result from males expending far more energy toward sexual reproduction than females, representing a reversal of roles found in most species of plants and animals. Predictions from this hypothesis include that males should be more vulnerable to stress than females, because females have more available resources to expend on stress tolerance. Stresses that will be studied include high temperatures, tolerance to drying out, and tolerance to receiving intense summer rainfall events, with the latter events representing a combination of high temperatures followed by quick drying of plant tissues. Following application of stress to plant tissues of each sex, growth and recovery will be monitored using a variety of measures, including mortality, time to resumption of growth, shoots produced, growth rate, and the efficiency of photosynthesis. The approach seeks to expose plants of each sex to realistic stresses experienced in the field that should influence the growth responses of males and females of this moss, thereby helping gain an understanding of why males are so rare. The research should also help to clarify one of the patterns that exist across all of the mosses, male rarity, which appears to be especially manifested in deserts. The project impacts include direct connections to impacts of climate change and increasing opportunities to involve minority students in research.
