Bryoecology in the American southwest: Patterns of biodiversity and responses to global change

This dissertation combines investigation of the large-scale responses of bryophyte species diversity and distribution with small-scale physiological adaptations to global change. These two areas of inquiry are linked because one way to predict plant species responses to global change is to examine their distribution across current ecological gradients produced by factors such as latitude and elevation. By examining these biogeographic patterns one can identify those species that have a narrow tolerance and therefore are most sensitive to change. Selected bryophytes might then be used as indicator species in long-term monitoring programs. Where historical data exist, these can be used to reconstruct the past and continuing range shifts of bryophytes in response to decades of global change.;In chapter 2 a checklist of the 310 bryophyte taxa (two hornworts, 46 liverworts and 262 mosses) reported to occur within the political boundaries of the state of Nevada is presented. 238 new county records are also listed. Notes are provided for species with complex synonymies, taxonomic difficulties or interesting histories. This checklist is intended to improve efforts towards a complete bryophyte flora of the state by identifying those species, habitats and geographic regions that have been neglected or poorly sampled. Chapter 4 describes a baseline assessment of the bryophyte diversity on the Grand Canyon-Parashant National Monument. Collecting locations were selected in order to maximize the number of species collected and to cover the monument both geographically and ecologically. Forty-seven sites were visited and 679 voucher specimens were collected. A checklist, flora and photographic guide were prepared for the 110 species identified from among these collections.;Finally, chapter 3 describes an experiment where intact Mojave desert scrub and associated biological soil crust were exposed over multiple years to experimental treatments designed to simulate predicted global change. Field treatments included a FACE (Free Air Carbon dioxide Enrichment) site where plants were exposed to experimentally elevated atmospheric CO2 (550 ppm). In order to determine the responses of the bryophyte component of the soil crust to elevated CO2 concentrations, patches of the dominant Mojave Desert moss Syntrichia caninervis Mitt. were sampled from the FACE treatments. Shoots grown under elevated CO2 expressed sex more frequently and tolerated repeated cycles of desiccation better than their ambient counterparts. In a follow-up experiment, plants were grown at both elevated and ambient CO2 concentrations in the laboratory. All plants grown at elevated CO2 under laboratory conditions exhibited greater regenerational vigor than plants grown at ambient CO 2; however there were interaction effects between the laboratory and field treatments that suggest photosynthetic down-regulation is occurring. It appears that while they are capable of harnessing additional CO2 for growth, in the harsh conditions of their native environment these plants preferentially allocate those added resources to sexual reproduction and stress tolerance. Biological soil crusts perform several valuable ecosystem functions in arid regions so it is important that we understand their responses under various scenarios of global change.