Influence of Biocrusts and Seed Morphology on Emergence and Establishment of Grasses in Two North American Deserts

Covering roughly one-third of the Earth’s terrestrial area, drylands support approximately 20% of the global population. Biocrusts (biological soil crusts) occupy plant interspaces and provide a variety of ecosystem services in drylands. Grasses are also an important component of drylands, but non-native grasses are invading and altering these ecosystems. Biocrusts and plants interact, including at the initial stages of plant recruitment. The research described in this dissertation focused on the Sonoran Desert and Colorado Plateau and utilized a coordinated set of experiments to investigate how interactions between biocrust attributes (i.e., source desert, development, and integrity) and grass attributes (i.e., nativity and seed characteristics) might influence grass emergence and early establishment. It also includes an experiment investigating the effect of inocula crumble size on biocrust restoration success. I first investigated the effect of biocrusts on grass emergence/early establishment based on grass nativity, and substrate type and source. I found that biocrusts do not consistently inhibit non-native grasses compared to native grasses but do reduce emergence/early establishment relative to bare soil in some experimental settings. Furthermore, Sonoran Desert biocrusts reduced emergence relative to bare soil more than Colorado Plateau biocrusts for two native grasses. I next compiled morphological attributes of grass seeds and investigated the role of those attributes, including appendages (e.g., awns, bristles), on emergence and establishment outcomes on biocrusts. Sonoran Desert and Colorado Plateau grass species have a wide range of seed shapes, sizes, and appendages. However, my experiments did not reveal consistent patterns in emergence/establishment on biocrusts based on seed characteristics. Clipping awns and trimming bristles from seeds had species-specific effects on emergence, but no effect on early establishment. Next, I evaluated emergence/early establishment based on biocrust integrity and seed location. Breaking biocrusts and placing seeds in cracks of otherwise intact biocrusts increased emergence and/or early establishment for most grass species. I measured naturally occurring cracks in biocrusts and found that they are transitory. Finally, I investigated the role of inocula crumble size on the restoration of biocrust cover following disturbance and found that large lichen fragments yielded better results than smaller fragments. Together, this research elucidates the role of biocrusts in grass recruitment and contributes to the biocrust restoration knowledge-base