Freezing stress influences emergence of germinated perennial grass seeds

Authors: Boyd, Chad; Lemos, Jarod

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2013
Publication Date: 3/1/2013
Citation: Boyd, C.S., Lemos, J.A. 2013. Freezing stress influences emergence of germinated perennial grass seeds. Rangeland Ecology and Management. 66(2):136-142. https://doi.org/10.2111/REM-D-12-00135.1.
DOI: https://doi.org/10.2111/REM-D-12-00135.1

Interpretive Summary: In sagebrush rangelands perennial bunchgrasses are typically seeded in fall and a high proportion of planted seeds germinate prior to winter onset but fail to emerge in spring. Our objectives were to evaluate freezing tolerance of germinated but non-emergent bluebunch wheatgrass seedlings under laboratory conditions. Our results indicate that density of emergent seedlings is dramatically reduced (at least 4-fold) with freezing during early, mid or late germination stages, and that these effects can occur within 2-days of the onset of frozen soil conditions. From a management standpoint, these data imply that timing of germination may be critical to emergence and establishment of fall-planted bluebunch wheatgrass; altering timing of planting to a later calendar date could reduce the amount of germination prior to frozen soil conditions in winter and subsequent freeze-related mortality of germinated seeds.

Technical Abstract: In sagebrush rangelands perennial bunchgrasses are typically seeded in fall and a high proportion of planted seeds germinate prior to winter onset but fail to emerge in spring. Our objectives were to evaluate freezing tolerance of germinated but nonemergent bluebunch wheatgrass seeds under laboratory conditions. We used data from a 2-yr pilot study to determine overwinter freezing temperature and duration for soils in southeastern Oregon. We then conducted two experiments to assess freezing tolerance. In experiment 1, bluebunch wheatgrass seeds were planted in control pots and compared to seeds planted at early, mid, or late postgermination stages. Pots from each treatment were placed in a grow room maintained at 12 h 40 min light/11 h 20 min dark photoperiod, with a constant temperature of 22°C for 30 d either immediately or following a 30-d freeze. In experiment 2, germinated bluebunch wheatgrass seeds were planted in pots that were left nonfrozen or were frozen for a specified duration prior to a 30-d period in the grow room. Emergence density and tillers'·'seedling-1 were quantified for both experiments. The number of days per year for freezing soil conditions in the pilot study ranged yearly from 25 to 51; maximum duration of continuous freezing was 16.5 and 11.2 d. Freezing reduced or eliminated seedling emergence at all postgermination stages (P'<'0.001) and tiller density was reduced by at least 50% (P'<'0.001). Maximum reduction in seedling density (P'<'0.001) was realized within 4 d of initiation of freezing and tillers'·'seedling-1 were reduced 30–70% with >'6 d of freezing (P'='0.001). Our data indicate that freezing-associated mortality of germinated but nonemergent bluebunch wheatgrass seedlings can be extremely high and suggest that management practices to reduce prewinter germination of seeds could improve subsequent emergence and seeding success.