Seed Dormancy and Soil Seed Bank of the Two Alpine Primula Species in the Hengduan Mountains of Southwest China

The influence of climate change on Primula Sect. Crystallophlomis in southwest China

PURPOSE

Climate change significantly affects the distribution of high-altitude plant species, particularly within the Primula Sect. Crystallophlomis found in Southwest China. This clade is valued for its ornamental and medicinal properties. This study aims to evaluate the impact of climate change on the potential distribution of P. crystallophlomis to inform conservation and ecological research.

METHODS

An optimized Maximum Entropy model (MaxEnt) was utilized to predict the suitable habitat areas of P. crystallophlomis under 9 scenarios, using 161 distribution records and 22 environmental variables. The model parameters were set to RM = 1.5 and FC = LQH, achieving a high prediction accuracy with an Area Under the Curve (AUC) value of 0.820.

RESULTS

The analysis identified key environmental factors influencing the suitable habitat of P. crystallophlomis, including annual precipitation (bio-12), temperature seasonality (bio-4), mean diurnal range (bio-2), and precipitation seasonality (bio-15). Under current climate conditions, the suitable habitats are primarily located in the eastern Qinghai-Tibet Plateau, Hengduan Mountains, and Yunnan-Guizhou Plateau, exhibiting significant fragmentation. Notable declines in potential habitat area were observed from the Last Glacial Maximum (LGM) to the Mid-Holocene (MH), with future projections indicating further reductions, particularly under the Shared Socioeconomic Pathways 585 (SSP-585) scenario.

CONCLUSION

The suitable habitat of P. crystallophlomis, which tends to grow in consistently cold and moist environments, is expected to shrink, with a projected southward shift in its centroid. Global warming is anticipated to profoundly impact the suitable habitats of P. crystallophlomis, highlighting the urgent need for conservation efforts.

The preemptive control strategy for invasive plant seed banks triggering ecological threats through synchronized germination

Invasive alien plants threaten global ecosystems by disrupting biodiversity and degrading ecological functions. Soil seed banks-the reservoirs of viable seeds in the soil-play a crucial role in the persistence and spread of plant populations. However, current control measures for invasive plants predominantly target above-ground vegetation, neglecting these underground seed reserves, thereby allowing invasive plants to re-establish their populations. Inducing synchronous germination to deplete seed banks offers a potential preemptive control strategy. This study hypothesizes that seeds of invasive plants secrete secondary metabolites to promote the synchronous germination of conspecific seeds. Focusing on Ambrosia trifida L., a globally harmful annual invasive plant, where the soil seed bank plays a crucial role in its continued impact. We used metabolomics to identify such metabolites and found that Angelicin significantly enhances germination rates by up to 116.9 % (P < 0.01). Field experiments conducted in the native habitat demonstrated that applying Angelicin at concentrations of 0.015 μg ml-1 or higher depleted over 85 % of the seed bank (P < 0.01) without harming indigenous plant communities. These findings confirm the feasibility of depleting underground seed banks through induced germination. Integrating this strategy with traditional above-ground control methods can develop a comprehensive management system, offering a promising new approach for the widespread control of invasive plants.

Mother-reliant or self-reliant: the germination strategy of seeds in a species-rich alpine meadow is associated with the existence of pericarps

BACKGROUND AND AIMS

Some plants germinate their seeds enclosed by a pericarp, whereas others lack the outer packaging. As a maternal tissue, the pericarp might impart seeds with different germination strategies. Plants in a community with different flowering times might separately disperse and germinate their seeds; therefore, flowering time can be considered as one manifestation of maternal effects on the offspring. The mass of the seed is another important factor influencing germination and represents the intrinsic resource of the seed that supports germination. Using seeds from a species-rich alpine meadow located in the Hengduan Mountains of China, a global biodiversity hotspot, we aimed to illustrate whether and how the type of seed (with or without a pericarp) modulates the interaction of flowering time and seed mass with germination.

METHODS

Seeds were germinated in generally favourable conditions, and the speed of germination [estimated by mean germination time (MGT)] was calculated. We quantified the maternal conditions by separation of flowering time for 67 species in the meadow, of which 31 produced seeds with pericarps and 36 yielded seeds without pericarps. We also weighed 100 seeds of each species to assess their mass.

KEY RESULTS

The MGT varied between the two types of seeds. For seeds with pericarps, MGT was associated with flowering time but not with seed mass. Plants with earlier flowering times in the meadow exhibited more rapid seed germination. For seeds without a pericarp, the MGT depended on seed mass, with smaller seeds germinating more rapidly than larger seeds.

CONCLUSIONS

The distinct responses of germination to flowering time and seed mass observed in seeds with and without a pericarp suggest that germination strategies might be mother-reliant for seeds protected by pericarps but self-reliant for those without such protection. This new finding improves our understanding of seed germination by integrating ecologically mediated maternal conditions and inherent genetic properties.

Non-deep physiological dormancy and germination characteristics of Primula florindae (Primulaceae), a rare alpine plant in the Hengduan Mountains of southwest China

Timing of seed germination is directly related to the survival probability of seedlings. For alpine plants, autumn-dispersal seeds should not germinate immediately because the cold temperature is not conducive to the survival of seedlings. Seed dormancy is a characteristic of the seed that prevents it from germinating after dispersal. Primula florindae is an alpine perennial forb endemic to eastern Tibet, SW China. We hypothesized that primary dormancy and environmental factors prevent seeds of P. florindae to germinate in autumn and allow them to germinate at the first opportunity in spring. We determined how GA₃, light, temperature, dry after-ripening (DAR) and cold-wet stratification (CS) treatments affect seed germination by conducting a series of laboratory experiments. Firstly, the effects of gibberellic acid (GA₃; 0, 20, and 200 mg L^-1) on germination of freshly shed seeds at alternating temperatures (15/5 and 25/15 °C) were immediately investigated to characterize seed with a physiological dormancy component. Then, the fresh seeds treated with 0, 3, and 6 months of after-ripening (DAR) and cold-wet stratification (CS) were incubated at seven constant (1, 5, 10, 15, 20, 25, and 30 °C) and two alternating temperatures (5/1, 15/5, and 25/15 °C) at light and dark conditions. Fresh seeds were dormant, which only germinated well (>60%) at 20, 25, and 25/15 °C in light but not at ≤15 °C and to higher percentages in light than in dark. GA₃ increased germination percentage of fresh seeds, and DAR or CS treatments increased final germination percentage, germination rate (speed), and widened the temperature range for germination from high to low. Moreover, CS treatments reduced the light requirement for germination. Thus, after dormancy release, seeds germinated over a wide range of constant and alternating temperatures, regardless of light conditions. Our results demonstrated that P. florindae seeds have type 2 non-deep physiological dormancy. Timing of germination should be restricted to early spring, ensuring a sufficient length of the growing season for seedling recruitment. These dormancy/germination characteristics prevent seeds from germinating in autumn when temperatures are low but allow them to germinate after snowmelt in spring.