Overview. The central theme of my current research revolves around the stress biology of mosses. Types of stress responses under study include desiccation tolerance (DT), thermotolerance, and exposure toprojected climate change stressors such as elevated CO2, summer precipitation events, nutrient additions, and microsite disturbance. The principal species under study is the dominant desert moss Syntrichia caninervis, with other species in the genera Tortula, Pterygoneurum, and Crossidium. The three subthemes deriving from stress biology include (i) understanding sex dimorphic responses of stress in dioecious species exhibiting skewed sex ratios, including assessing the "cost of sex" hypothesis; and (ii) exploring the effects of climate change on the growth, reproduction, establishment, and disturbance recovery of desert mosses. In addition to the theme of stress biology, I am involved in tracking the status of globally rare species of bryophytes in the Mojave Desert and developing a list of bryophytes known from the state of

Nevada. Research in progress is funded by the National Science Foundation, the U.S. Department of Energy's National Institute for Global Environmental Change (NIGEC), the Clark County (NV) Multiple Species Habitat Conservation Plan, and the National Geographic Society. My collaborators with these projects include D. Nicholas McLetchie (University of Kentucky), Brent Mishler (UC Berkeley), Mel Oliver (USDA Plant Stress Lab, Columbia, MO), Jayne Belnap (US Geological Survey, Moab, UT), Stan Smith (UNLV), Jim Shevock (US National Park Service), John Spence (US National Park Service), and John Brinda (UNLV). Specific current projects involve graduate and undergraduate student research (with prospective graduate students and postdoctoral student applications welcome), and include:

1. Sex-specific regeneration patterns in response toimposed stress. A major unanswered question in the reproductive biology of mosses is why are males so rare? Sex ratios in dioecious mosses around the world generally exhibit the pattern of male rarity, and this pattern seems to be extreme in arid mosses. Preliminary data from the Mojave Desert indicates that sex ratios as unbalanced as 25 female plants for every male plant are commonplace, and frequently the male plants are absent entirely from populations. Our hypothesis is that male individuals incur a greater allocational investment of sexual expression and reproduction, and that this cost compromises their clonal vigor. When leaves or shoots are regenerated in culture under unstressed conditions (simulating winter in the desert), females tend to produce shoots more rapidly than males, and also to produce more shoots from secondary protonemata than males. This indicates that females of Syntrichia caninervis may be at a clonal advantage with respect to shoot production. Current projects explore the regenerative response of gametophytes after exposure to these stresses:

a. Desiccation tolerance: exposure to alternating cycles of wet/rapid-dry.

b. Thermostress when wet: exposure to sublethal temperatures up to 40C.

c. Thermostress when dry: exposure to sublethal temperatures up to 120C.

d. Desiccation stress in combination with heat stress: exposure to conditions simulating a summer rainstorm, where the plants are exposed to, in repeated cycles, hot temperatures when dry, warm temperatures when moist, and then a rapid-desiccation cycle.

e. Nutrient deprivation: exposure to a decreasing nutrient regime.

f. Light stress: exposure to an increasing light intensity regime, to include UVB radiation.

g. Cost of sexual reproduction: exposure of maternal gametophytes carrying embryonic sporophytes to stresses such as thermostress,desiccation, perichaetial leaf removal, or nutrient deprivation.

2. Climate change responses. Current models projecting future climate patterns suggest that the Mojave Desert will receive a pattern of increasing summer precipitation (monsoon effect), elevated levels of atmospheric nitrogen deposition, and elevated levels of soil disturbance, with the latter two projections based on continued human population growth in the region. The biological soil crust is well developed in pristine regions of the Mojave, and we have access to the only hot desert FACE facility (Free-Air CO2 Enrichment) and global change facility (MGCF, Mojave Global Change Facility), based on the Nevada Test Site approximately 70 miles north of Las Vegas. This facility offers a field station and restricted public access, thus providing scientists an area to conduct sensitive field experiments. The dominant moss in the Mojave is Syntrichia caninervis; this species is the subject of a series of ecophysiological assessments that combine field and lab experiments, with response variables to include annual growth/productivity, sex expression/reproduction, chlorophyll fluorescence, pigment analyses, and responses to desiccation and temperature stresses outlined above. Long-term field experimental treatments include:

a. Elevated CO2: how do individuals of Syntrichia respond to elevated levels of carbon dioxide?

b. Increased summer precipitation: how do individuals of Syntrichia respond to additional summer rainfall?

c. Patch disturbance: how do patches respond to low and high levels of disturbance, in terms of recolonization?

d. Increased nitrogen deposition: how to individuals of Syntrichia respond to low and high levels of nitrate supplementation?

3. Bryofloristics of the Mojave Desert and state of Nevada. In conjunction with Jim Shevock, John Spence, and John Brinda, a survey the bryophytes of Nevada is underway. My focus is upon the Mojave Desert, with special attention to globally or state-rare species of bryophytes in Clark County, NV. Rare species of note include the southwestern endemics Didymodon nevadensis, Grimmia americana, Trichostomum sweetii, and a soon-to-be described species in the genus Targionia.

4. Other Research Areas of interest. Research areas not falling into the categories above include aspects of reproductive biology, comparative desiccation tolerance and thermotolerance of sporophytes and gametophytes, assessing the seasonality of desiccation and thermostress, and the phenology of hydration in desert mosses.