Seed-Specific Mass and Root Growth Relate to Perennial Bunchgrass Seedling Survivorship under Highly Limited Nutrient Supply

Maternal provisioning to seeds is critical to later plant success, and identifying seed traits that predict successful plant establishment and resilience may facilitate improved plant material selection for rangeland restoration. Although size-standardized measurements are typically recorded for leaf traits, this is not the case for seed traits. In this study, we investigated whether an area-standardized metric, seed-specific mass (SSM), was better associated with seedling performance relative to simple seed mass. We germinated seeds of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh.] A. Löve), crested wheatgrass (Agropyron cristatum L. var. Hycrest II), and Sandberg bluegrass (Poa secunda Presl.) on sterile agar and tracked seed mass, SSM, and subsequent seedling growth and mortality to investigate relationships between seed traits and seedling performance. SSM showed clear variation among species despite similarities in seed mass, and species-specific patterns of mortality most closely tracked variation in SSM. Crested wheatgrass seedlings that survived to 52 wk had significantly greater SSM than those that perished during the study, and surviving seedlings also had significantly longer roots at wk 4 than those that died. Seed mass and SSM each explained variation in seedling traits to some extent. Simple seed mass best predicted variation in early leaf area within species, while root length was best predicted by SSM across species. Our study is indicative that SSM warrants consideration in future studies investigating maternal energetic provisioning and seedling performance.