Seed dormancy types and germination characteristics of six plants in the dry-warm valley of Jinshajiang River, SW China

Abstract

Seed dormancy and the requirements for germination following dormancy release are critical factors influencing the success of seedling establishment. This study examined six plant species from the dry-warm valley region of the Jinshajiang River in southwestern China, investigating their seed dormancy types and germination characteristics. Initially, germination tests were conducted using freshly matured seeds at alternating temperatures of 25/15 and 15/5 °C under light conditions. Subsequently, after dry after-ripening (DAR), germination was retested. Additionally, dried seeds were incubated under a range of constant temperatures (5-37 °C) under light conditions. The effects of darkness and GA₃ on seed germination were evaluated at alternating temperatures of 25/15 and 15/5 °C. Cardinal temperatures and thermal time requirements for 50% final germination (θ ₅₀) were determined. The increase in final germination following seed coat scarification indicated that Sophora davidii seeds exhibited physical dormancy at dispersal. Treatment with DAR and/or GA₃ effectively alleviated dormancy in the other five species (Osteomeles schwerinae, Excoecaria acerifolia, Leonurus japonicus, Incarvillea arguta, Berberis concolor), particularly at the cooler temperature regime of 15/5 °C, suggesting that these species possess non-deep physiological dormancy. Once dormancy is alleviated, seeds of all six plant species can germinate across a broad temperature spectrum, and the temperature window (T _b-T _c) for germination is much wider than the actual germination range. Alternating temperatures did not significantly enhance germination rates compared to constant temperatures, except for L. japonicus. Seeds of L. japonicus exhibited a strict light requirement for germination at alternating temperatures of 25/15 and 15/5 °C, whereas the other five plant species germinated effectively in darkness at the warmer alternating temperature of 25/15 °C. Thus, our hypothesis that dormancy and germination traits restrict germination to the summer (rainy season) is supported. This ensures that seedlings can establish themselves once soil moisture and temperature conditions become favorable. This research offers a valuable scientific reference for vegetation restoration efforts in dry-warm valley regions.

Keywords: Cardinal temperatures; Dry after-ripening; Dry valley; Light requirement; Non-deep physiological dormancy.

Figure 1. Imbibition curves of intact (black line) or manually scarified (red line) seeds and morphological structure of seeds of six study species.

Water uptake data are means ± SE (n = 4). The dashed line indicates the outline of the embryo; for exalbuminous seeds, the embryo is not drawn separately with a dashed line.

Figure 2. Final germination percentages (n = 3, means ± SE) at two alternating temperatures for fresh, dry after-ripened (DAR) and DAR + GA₃ seeds of six species.

All germination percentages shown in this figure were obtained under light conditions. 0, no germination at this treatment. Bars with different uppercase letters indicate significant differences (P < 0.05) in germination percentage between fresh and DAR seeds, and different lowercase letters indicate significant differences (P < 0.05) between DAR and DAR + GA₃ seeds at each temperature.

Figure 3. Effects of light condition on germination percentage (n = 3, means ± SE) for DAR seeds of six species at two alternating temperatures.

The seeds of Sophora davidii in this figure were subjected to seed coat scarification. 0, no seeds germinated in this treatment. * P < 0.05, ** P < 0.01, and *** P < 0.001, ns, not significant.

Figure 4. Effects of temperature on germination percentage and mean germination time (MGT) (n = 3, means ± SE) for DAR seeds of six species at light condition.

The seeds of Sophora davidii in this figure were subjected to seed coat scarification. ×, no test in this treatment; 0, no germination at this temperature. Bars with different uppercase letters indicate significant differences (P < 0.05) for germination percentage, and scatters with different lowercase letters indicate significant differences (P < 0.05) for MGT at different temperatures.

Figure 5. Effect of alternating and corresponding constant temperatures (LT, low temperature; 15/5 vs. 10 °C; HT, high temperature; 25/15 vs. 20 °C) on final germination percentage (n = 3, means ± SE).

All germination percentages shown in this figure were obtained under light conditions. 0, no seeds germinated in this treatment. ** P < 0.01, ns, not significant.

Figure 6. Curve fitting of linear model to germination rate (1/t₅₀) versus temperature at constant temperatures (5–37 °C) for DAR seeds in six species.

Germination rates (n = 3, means ± SE) calculated on the basis of the reciprocal of the times to reach 50% final germination. Points correspond to the actual data and red solid lines indicate the fitted lines from the linear regressions.