Limits to Sexual Reproduction in Geothermal Bryophytes

Previous research suggests that while sexual reproduction generally increases with environmental stress it may decrease with extreme stress, at the edge of eukaryotic life. In this study, we explored the limits to sexual reproduction in an extremophile, bryophyte system to ultimately understand the processes that limit sexual reproduction. We used field data from geothermal sites at Lassen Volcanic National Park, California, to demonstrate that sexual reproduction, as measured by the number of sporophytes per shoot, decreases with increasing environmental stress. We found that the number of sporophytes per shoot is positively correlated with distance from geothermal features. When Pohlia nutans plants were transplanted to mesic conditions, high numbers of gametoecia and sporophytes were produced, regardless of where along the environmental stress gradient plants originated, suggesting that physiological stress rather than local adaptation is constraining sexual reproduction in this extremophile system. We discuss our results with respect to previous work on sex in extreme environments

Sex-Specific Variation in the Interaction Between Distichlis Spicata (Poaceae) and Mycorrhizal Fungi

Associations between mycorrhizal fungi and plants can influence intraspecific competition and shape plant population structure. While variation in plant genotypes is known to affect mycorrhizal colonization in crop systems, little is known about how genotypes affect colonization in natural plant populations or how plant sex might influence colonization with mycorrhizal fungi in plant species with dimorphic sexual systems. In this study, we analyzed mycorrhizal colonization in males and females of the wetland dioecious grass Distichlis spicata, which has spatially segregated sexes. Our results suggest that D. spicata males and females interact with mycorrhizal fungi differently. We discuss the implications for the role of this sex-specific symbiotic interaction in the maintenance of the within-population sex ratio bias of D. spicata

Distribution Drivers and Physiological Responses in Geothermal Bryophyte Communities

Premise of Study: Our ability to explain community structure rests on our ability to define the importance of ecological niches, including realized ecological niches, in shaping communities, but few studies of plant distributions have combined predictive models with physiological measures. Methods: Using field surveys and statistical modeling, we predicted distribution drivers in geothermal bryophyte (moss) communities of Lassen Volcanic National Park (California, USA). In the laboratory, we used drying and rewetting experiments to test whether the strong species-specific effects of relative humidity on distributions predicted by the models were correlated with physiological characters. Key Results: We found that the three most common bryophytes in geothermal communities were significantly affected by three distinct distribution drivers: temperature, light, and relative humidity. Aulacomnium palustre, whose distribution is significantly affected by relative humidity according to our model, and which occurs in high-humidity sites, showed extreme signs of stress after drying and never recovered optimal values of PSII efficiency after rewetting. Campylopus introflexus, whose distribution is not affected by humidity according to our model, was able to maintain optimal values of PSII efficiency for 48 hr at 50% water loss and recovered optimal values of PSII efficiency after rewetting. Conclusions: Our results suggest that species-specific environmental stressors tightly constrain the ecological niches of geothermal bryophytes. Tests of tolerance to drying in two bryophyte species corresponded with model predictions of the comparative importance of relative humidity as distribution drivers for these species