Population-level variation in germination cues and possible relationships to source climate for native forb species used in restoration

Seed germination is a critical step in the life history of plants. The seeds of many arid land plants delay germination until the seeds receive environmental cues that stimulate them to grow. These dormancy-breaking cues may vary among populations of the same plant species, depending on their local environmental conditions, and can determine the selection pressures experienced during plant growth and establishment.

Seed germination is a potential bottleneck to plant establishment. Identifying population-level variation in response to seed dormancy-breaking cues and potential relationships to environmental conditions will improve restoration success through the appropriate selection of seed for use in restoration.

Incorporating forbs into restoration seed mixes is important for restoring diversity to native plant communities and supporting ecosystem function, such as habitat for threatened wildlife populations. The results of this research will be used to inform seed transfer guidance for restoration practitioners.

Approach

A map of the locations of the focal populations of M. canescens and C. douglasii. Seeds originate from 19-20 populations for each species, representing the range of environments where they grow.

1. Focal species were selected because of their value as forage and cover resources for wildlife (e.g. sage grouse and pollinators). The focal species for the germination study will be a subset of the species used in the associated common garden project, including: Chaenactis douglasii, Machaeranthera (Dieteria) canescens, Erigeron pumilus, Phacelia hastata, Balsamorhiza sagittata, and Crepis acuminata.
2. Seed was collected from many populations across the environmental range of each species, as part of the common garden project. Seed from a subset of the populations used in the common garden project will be used to test for population-level variation in germination response to dormancy-breaking cues.
3. A subset of ~20 focal populations was selected, representing a variety of environmental conditions, for each of our study species.
4. Germination chambers are being used to apply cold stratification treatments at 2◦C for 0, 2, 6, and 10 weeks. After the cold stratification treatment is complete, dishes are moved to a 15◦C germination chamber. All dishes are monitored for germination on a weekly basis for at least 14 weeks.
5. Statistical analyses will be used to determine differences in the quantity and rate of germination among populations. Germination data will also be used to uncover potential relationships between germination strategies and conditions at seed source environments.
6. This project will result in early life-history data that can be incorporated into seed transfer guidance for restoration practitioners, as well as research publications from RMRS scientists covering topics related to local adaptation and climate change effects.

Key Findings

Germinating seeds in petri dishes. Seeds of focal species A) C. douglasii and B) M. canescens were placed on moistened germination paper in petri dishes. Seed germination, in response to different lengths of cold stratification, was monitored weekly for at least 14 weeks.

• Preliminary observations for Chaenactis douglasii indicate population differences in germination strategies. While many seeds germinated in the 15◦C treatment, after experiencing cold stratification, seeds from some populations were able to germinate in the 2◦C treatment.
• Viability for Chaenactis douglasii seeds remained relatively high, even after two years of storage at room temperature. TZ tests showed an average viability of 89% ± 8% across all populations.
• The germination trial for Machaeranthera (Dieteria) canescens began in August 2021.
• Additional species will be incorporated on a rotating basis, with Erigeron pumilus being the next species to be added in January 2022.