Seed germination and dormancy traits of forbs and shrubs important for restoration of North American dryland ecosystems

Abstract

In degraded dryland systems, native plant community re-establishment following disturbance is almost exclusively carried out using seeds, but these efforts commonly fail. Much of this failure can be attributed to the limited understanding of seed dormancy and germination traits. We undertook a systematic classification of seed dormancy of 26 species of annual and perennial forbs and shrubs that represent key, dominant genera used in restoration of the Great Basin ecosystem in the western United States. We examined germination across a wide thermal profile to depict species-specific characteristics and assessed the potential of gibberellic acid (GA ) and karrikinolide (KAR ) to expand the thermal germination envelope of fresh seeds. Of the tested species, 81% produce seeds that are dormant at maturity. The largest proportion (62%) exhibited physiological (PD), followed by physical (PY, 4%), combinational (PY+PD, 4%), and morphophysiological (MPD, 1%) dormancy classes. The effects of chemical stimulants were temperature- and species-mediated. In general, mean germination across the thermal profile was improved by GA and KAR for 11 and five species, respectively. We detected a strong germination response to temperature in freshly collected seeds of 20 species. Temperatures below 10°C limited the germination of all except Agoseris heterophylla, suggesting that in their dormant state, the majority of these species are thermally restricted. Our findings demonstrate the utility of dormancy classification as a foundation for understanding the critical regenerative traits in these ecologically important species and highlight their importance in restoration planning. This article is protected by copyright. All rights reserved.

Dormancy and germination: making every seed count in restoration

“…Restoration practitioners must be able to correctly assign seed dormancy classes because treatments to alleviate seed dormancy are specific to each class (Silveira ; Erickson et al ; Kildisheva et al ; Kildisheva ). Applying the wrong treatment can at best result in failure to break dormancy and at worst kill the seeds.…”

“…Physically dormant seeds will germinate rapidly and to a high extent after scarification. If germination is low even after scarification, this implies poor growth potential of the embryo induced by physiological dormancy; such seeds have combinational (physical + physiological) dormancy (Baskin & Baskin ; Kildisheva et al ).…”

Maximising the use of native seeds in restoration projects

“…Kildisheva et al . () classified the seed dormancy of 26 key species of the dryland ecosystem of the Great Basin in the USA using a wide temperature range and applying gibberellic acid and karrikinolide, well known dormancy‐breaking compounds. Various dormancy types (physiological, physical, a combination of the two and morphophysiological) were observed and, in all but one species, germination was inhibited below 10 °C.…”

Seed enhancement: getting seeds restoration‐ready

“…Interestingly, the addition of GA 3 to the osmo‐priming solution promoted germination in suboptimal conditions (e.g. drought, light/dark) or substituted for the temperature fluctuation requirement of some species, thus expanding the germination “niche” of the tested species to a wider range of environmental conditions (Wagner et al ; Lewandrowski et al ; Kildisheva et al ).…”

“…The ability to promote more rapid germination across a wider range of conditions may be particularly salient in regions where environmental conditions are highly stochastic, such as drylands (Pedrero‐López et al ; Erickson et al ; Kildisheva ). Erickson et al () and Kildisheva et al () reported on the potential for the integration of seed priming into the restoration tool kit in the context of mine rehabilitation, either alone or in combination with other seed enhancement techniques. Priming with karrikinolide, a smoke‐derived germination stimulant, was shown to improve germination and emergence of Triodia pungens L. (Erickson et al ; Kildisheva )—a keystone species in the Pilbara bioregion of Western Australia (Nicholas et al ).…”