Seed type and origin-dependent germination patterns in Danthonia californica, a cleistogamous species commonly used in grassland restoration

Abstract

Danthonia californica is a native perennial bunchgrass commonly used in the restoration of prairie ecosystems in the western United States. Plants of this species simultaneously produce both chasmogamous (potentially outcrossed) and cleistogamous (obligately self-fertilized) seeds. Restoration practitioners almost exclusively use chasmogamous seeds for outplanting, which are predicted to perform better in novel environments due to their greater genetic diversity. Meanwhile, cleistogamous seeds may exhibit greater local adaptation to the conditions in which the maternal plant exists. We performed a common garden experiment at two sites in the Willamette Valley, Oregon to assess the influence of seed type and source population (eight populations) on germination and found no evidence of local adaptation for either seed type. Cleistogamous seeds outperformed chasmogamous seeds regardless of whether seeds were sourced directly from the common gardens (local seeds), or other populations (nonlocal seeds). Furthermore, average seed weight had a strong positive effect on germination success, despite the fact that chasmogamous seeds had significantly greater mass than cleistogamous seeds. At one common garden we observed that seeds of both types sourced from north of our planting site performed significantly better than local or southern-sourced seeds. We also found a significant seed type and distance-dependent interaction, with cleistogamous germination peaking approximately 125km from the garden, which may be explained by differences in the pathogen content of cleistogamous and chasmogamous seeds. These results suggest that cleistogamous seeds should be considered for greater use in D. californica restoration.