Seed dormancy-breaking in a cold desert shrub in relation to sand temperature and moisture

AoB PLANTS, Jan 2017

Seasonal periodicity of seed germination and its relationship to seasonal changes in temperature and soil moisture have been well studied in seeds of species with physiological dormancy. However, relatively little information is available on the role of these environmental factors in controlling germination of seeds with physical dormancy (PY). Our primary aim was to determine if seeds of the cold desert sand dune semi-shrub Eremosparton songoricum exhibits seasonal periodicity of seed germination and the relationship between seed dormancy break and soil temperature and moisture. In the laboratory, seeds incubated on dry, wet, wet-dry and dry-wet sand were exposed to a 1-year sequence of temperature regimes simulating those in the field. In the field, seeds were buried at different depths on a sand dune, and germination of periodically exhumed seeds was tested at five temperature regimes during a 2-year period. In the 1-year sequence of simulated natural temperature regimes, breaking of PY was more effective under constantly wet than under constantly dry conditions, and germination percentage was significantly higher under dry-wet than under wet-dry conditions. Seeds buried in the field exhibited a distinct peak of germination in spring and little or no germination in other seasons. The final (2-year) monthly cumulative germination percentage differed among burial depths and temperature, and it was highest (47 %) in seeds buried at 3 cm and tested at 25/10 °C. A seed cohort of E. songoricum likely exhibits a long-term annual periodicity of spring germination in the field, and dormancy break appears to be driven by low (winter) temperatures and relatively high sand moisture content. To our knowledge this is the first study to document seasonal periodicity in seed germination in a cold desert species with PY and to identify the mechanism (at the whole-seed level) of its occurrence.

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Seed dormancy-breaking in a cold desert shrub in relation to sand temperature and moisture

Abstract Seasonal periodicity of seed germination and its relationship to seasonal changes in temperature and soil moisture have been well studied in seeds of species with physiological dormancy. However, relatively little information is available on the role of these environmental factors in controlling germination of seeds with physical dormancy (PY). Our primary aim was to determine if seeds of the cold desert sand dune semi-shrub Eremosparton songoricum exhibits seasonal periodicity of seed germination and the relationship between seed dormancy break and soil temperature and moisture. In the laboratory, seeds incubated on dry, wet, wet-dry and dry-wet sand were exposed to a 1-year sequence of temperature regimes simulating those in the field. In the field, seeds were buried at different depths on a sand dune, and germination of periodically exhumed seeds was tested at five temperature regimes during a 2-year period. In the 1-year sequence of simulated natural temperature regimes, breaking of PY was more effective under constantly wet than under constantly dry conditions, and germination percentage was significantly higher under dry-wet than under wet-dry conditions. Seeds buried in the field exhibited a distinct peak of germination in spring and little or no germination in other seasons. The final (2-year) monthly cumulative germination percentage differed among burial depths and temperature, and it was highest (47 %) in seeds buried at 3 cm and tested at 25/10 °C. A seed cohort of E. songoricum likely exhibits a long-term annual periodicity of spring germination in the field, and dormancy break appears to be driven by low (winter) temperatures and relatively high sand moisture content. To our knowledge this is the first study to document seasonal periodicity in seed germination in a cold desert species with PY and to identify the mechanism (at the whole-seed level) of its occurrence. Burial depth, Eremosparton songoricum, Fabaceae, physical dormancy, seed germination phenology, wet-dry cycles Introduction Physical dormancy (PY) in seeds is caused by a water impermeable seed or fruit coat, and thus seeds cannot imbibe water when placed in a hydrated environment (Jayasuriya et al. 2013; Baskin and Baskin 2014). PY is present in at least 18 families of angiosperms including many taxa of Fabaceae (Baskin and Baskin 2014). Studies on the ecological factors affecting PY release have shown that high temperatures and/or dry heat (McKeon and Mott 1982; Lonsdale 1993; Norman et al. 2002), alternate wetting and drying (Baskin and Baskin 1984), wet heat (Van Klinken and Flack 2005; Van Klinken et al. 2006) and low (5°C) temperature (Van Assche et al. 2003) are effective for dormancy-break, depending on the species. Thus, temperature and moisture are expected to be the two critical factors that affect PY release in nature. Mature seeds with PY are dispersed from maternal plants and may become buried in the soil, where PY-break is controlled via soil temperature and moisture conditions (Hu et al. 2009; Baskin and Baskin 2014). As burial depth increases, the rate of PY release may decrease (Taylor and Ewing 1988; Van Klinken and Flack 2005; Van Klinken et al. 2006), increase (Hu et al. 2009) or increase and then decrease (Loi et al. 1999; Zeng et al. 2005). Burial depth is closely related to soil temperature and moisture. However, studies generally have focused on burial depth in relation to breaking of PY and have not been concerned with temperature or soil moisture (see Baskin and Baskin 2014). In the cold deserts of northwestern China, temperature is high in summer and low in winter, and amount and timing of rainfall is irregular. Based on available information from other systems, we infer that temperature, moisture and burial in the natural habitat affect PY release in seeds of cold desert species. To explore the breaking of PY in the cold desert, we selected Eremosparton songoricum (Litv.) Vass. (Fabaceae, Papilionoideae) as our study organism. This species is a perennial semi-shrub that is endemic to fixed and semi-fixed sand dunes of the Gurbantunggut Desert of Xinjiang Autonomous Region of northwest China and inland sand dunes around Lake Balkash in Kazakhstan (Yin et al. 2006; Zhang et al. 2008). Flowering occurs from late spring to early summer, and fruits are mature by mid- to late summer (Liu et al. 2011, 2013). The aboveground stems die in winter, and new shoots emerge from buried rhizomes or aerial-exposed stems the following spring (Wang et al. 2011). The dispersal unit is a pod that contains one or two seeds inside a papery pericarp (Liu et al. 2011; Zhang et al. 2011a). Plants are self-compatible, but pollination success relies on pollinators visiting the flowers to aid release of pollen onto the stigma (Zhang et al. 2011b). The species does not produce seeds by apomixis (Shi et al. 2010a, b; Zhang et al. 2011a, b). Freshly matured seeds of E. songoricum have PY, i.e. water-impermeable s (...truncated)


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Liu, Huiliang, Abudureheman, Buhailiqiemu, Zhang, Lingwei, Baskin, Jerry M., Baskin, Carol C., Zhang, Daoyuan. Seed dormancy-breaking in a cold desert shrub in relation to sand temperature and moisture, AoB PLANTS, 2017, Volume 9, Issue 1, DOI: 10.1093/aobpla/plx003