Biocrusts (biological soil crusts), communities of lichens, bryophytes, cyanobacteria and other microorganisms, live at the soil surface of semi-arid and arid regions globally. Biocrusts contribute to ecosystem services such as soil stability, hydrology, and nutrient cycling. Vascular plants and biocrusts interact is a variety of ways that changes over the lifespan of the plant. The influence of biocrusts on vascular plant germination can be negative, neutral, or positive. We seek to determine (i) if biocrust attributes, such as microtopography, intactness, and community composition, interact with seed morphology (shape, mass, appendages) to determine germination rates, and (ii) if biocrusts differentially affect the germination/early establishment of native and non-native grasses. As part of a broader project, we are using grass seeds of contrasting morphologies and seeds of native and non-native grass species in pot germination experiments in semi-controlled environments on the Colorado Plateau, where biocrusts are pinnacled, and in the Sonoran Desert, where biocrusts are comparatively smoother. We compared germination/emergence of grass seeds awns left intact or removed to determine the role of seed appendages. Seeds were scattered on the surface of intact or broken biocrusts or placed in fissures in the biocrusts.
Standardizing for seed viability, preliminary analysis shows that germination/emergence (mean ± SE) of grass seeds placed in fissures of Sonoran Desert lichen (55% ± 4) and cyanobacteria (54% ± 4) biocrusts was significantly higher (p<0.01) compared to seeds scattered on the surface of intact lichen (10% ± 1) or cyanobacteria (8% ± 1) biocrusts. For Colorado Plateau biocrusts, cheatgrass (Bromus tectorum) emergence was also highest (p<0.01) when seeds were placed in fissures. In the Sonoran Desert, emergence was also higher on broken lichen (32% ± 4) and cyanobacteria (21% ± 2) biocrusts compared to intact biocrusts. On intact biocrusts, non-native and native grasses emerged at similar rates, but larger native seeds (lemma lengths ≥ 10mm; awn lengths ≥ 30mm) emerged at lower rates (6% ± 1) compared to smaller native seeds (14% ± 1; lemma and awn lengths < 10mm). Contrary to expectations, removing the awns from non-native seeds had no effect and removing the awns from native seeds decreased germination on intact biocrusts in the Sonoran Desert. Removing awns may have altered water absorption by the natives. We speculate that seed-soil contact was higher for seeds placed in fissures or on broken biocrusts.