Can delaying germination reduce barriers to successful emergence for early-germinating, fall-sown native bunchgrass seeds in cold deserts?

Authors: BAUGHMAN, OWEN - The Nature Conservancy; KERB, JAY - Non ARS Employee; Boyd, Chad; MADSEN, MATTHEW - Brigham Young University; SVEJCAR, TONY - Retired ARS Employee

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: In cold desert ecosystems, fall-seeded perennial bunchgrasses often die during post-germination frozen soil conditions associated with winter thermal extremes. We tested the effects of coating perennial bunchgrass seeds with a germination-delay coating on timing of germination and resulting density of seeded species. Our results indicated that applying a germination-delay coating to seeds reduced pre-winter germination and resulted in higher seedling density of seeded species the following growing season. These results suggest that germination-delay coatings are a viable tool for reducing over-winter mortality of seeded perennial bunchgrasses and this technology could be used to bolster restoration success in cold desert environments.

Technical Abstract: Efforts to restore semi-arid wildlands in the western United States predominantly use fall seeding. Fall conditions are more amenable to seeding, and successfully over-wintered seeds are poised to take full advantage of spring moisture. However, winter mortality of fall-germinated seeds is a barrier to seeding success in some regions. One solution to avoid winter mortality without sacrificing the benefits of fall seeding is to delay germination of fall-sown seeds. At six field sites over three consecutive planting years in the northern Great Basin, we examined the effects of a seed treatment designed to delay germination compared to untreated seeds for a common native perennial bunchgrass. Specifically, we asked whether the treatment reliably delayed germination, and how the treatment and its effects were associated with seeding outcomes and/or interacting with year and site characteristics. Despite large variation among sites and through time, treated seed produced less pre-winter germination than untreated in all 18 trials (six sites, three years), and resulted in higher emerged seedling density in seven out of eight trials in which more than 50% of untreated seeds germinated pre-winter. We conclude that our treatments consistently delayed germination in the field, but only outperformed untreated seed when pre-winter germination was a barrier, which was common but not ubiquitous. These findings support continued experimentation with germination-delaying treatments and highlight the need for models that predict and define winter mortality risk. We suggest future exploration of bet-hedging by mixing treated and untreated seeds in areas at risk of winter mortality.