【Objective】 This study explored physiological and ecological mechanisms of seed vigor change in the canopy seed bank of Koelreuteria bipinnata in order to accurately understand the ecological significance of canopy seed banks.【Method】 A canopy seed bank of K. bipinnata was used as the object of study, and seeds were collected from the canopy seed bank at certain time intervals after fruits entered the ripening period. We then conducted a germination test and determined the seed dry mass, water content, malondialdehyde content, and activities of SOD, APX, CAT and DHAR. Finally, we performed an analysis between the germination percentage and physiological indices.【Result】 During the study duration, seeds in the canopy seed bank experienced four physiological periods, including physiological maturity, mature dehydration, dormancy induction and release. The seeds in each physiological period generally had the best germination under simulated autumn alternative temperatures, followed by spring alternative temperatures and summer alternative temperatures. The vigor of the seeds was maintained at a high level after mature dehydration was finished, and the four antioxidases played a significant positive role in the acquisition and maintenance of seed vigor, being significantly positive correlative with the germination percentages under simulated spring, summer and autumn alternative temperatures. Moreover, they all decreased with the induction of seed dormancy and increased with the release of dormancy, which also confirmed the “Embryo stress theory” of seed dormancy and germination.【Conclusion】 This study not only promotes further understanding of the canopy seed banks, but also finds that seeds in the canopy seed bank of K. bipinnata have a strong ability to maintain vigor. Full use of canopy seed banks in forest management and vegetation restoration should be encouraged.
【Objective】 To provide scientific references for germplasm conservation and development and utilization of Castanopsis carlesii, the geographical variations of seed morphological characteristics and nutrient content of C. carlesii from different provenances were analyzed. 【Method】 Seeds of C. carlesii were collected from 357 individuals growing in natural distribution areas of thirteen provenances. Six morphological characteristics (seed length, seed width, length width ratio, volume, surface area and 1 000-seed weight) and nutrients (soluble sugar and starch) of seeds were measured, and then variance, correlation and cluster analyses were conducted.【Result】 Seeds’ morphological characteristics were significantly different between and within provenances (P < 0.01); the mean values of seed length, width, length width ratio, volume, surface area and 1 000-seed weight ranged from 0.93-1.02 cm, 0.82-0.93 cm, 1.07-1.21, 0.32-0.46 cm3, 1.83-2.32 cm2 and 397.15-599.67 g, respectively. The nest analysis of variances showed that the maxima of seed length, width, volume, surface area, and 1 000-seed weight were observed in seeds from Jiangxi Dingnan (JXDN), and significantly differed from those from other provenances. The 1 000-seed weight of Anhui Qimen (AHQM) was 66.23% that of JXDN, and the seed length, width, volume and surface area were comparatively smaller. The percentages of starch and soluble sugar were 31.80% and 21.76%, respectively. The nutrient contents of C. carlesii were significantly different between provenances (P < 0.01); the coefficients of variation were 14.06% and 30.62%. The average coefficient of phenotypic differentiation was 28.15%, and genetic variation within provenances was the main source of the genetic variation of morphology characteristics. The correlation analysis showed that starch and 1 000-seed weight had the most positive correlations with seed width (P < 0.05), while sugar had an extremely significant correlation with seed length and length-width ratios (P < 0.01). Seed length showed a significant negative correlation with longitude (P < 0.05). The length-width ratio showed an extremely significant negative correlation to longitude (P < 0.01), and had significant negative correlation with precipitation during the coldest quarter (P < 0.05). The starch showed a significant correlation to annual mean temperature. The cluster analysis showed that the thirteen provenances could be divided into three groups. Group Ⅰ included JXDN, which possessed large sized seeds, high soluble sugar and high starch. Group Ⅱ included AHQM, Jiangxi Xinfeng (JXXF), Zhejiang Kaihua (ZJKH) and Guangdong Lianping (GDLP), which had small sized seeds, high soluble sugar and low starch groups; the other eight provenances fell into group Ⅲ, exhibiting medium sized seeds, and medium soluble sugar and starch contents. Adjacent provenances did not cluster together preferentially, indicating that there is no obvious geographical variation of C. carlesii.【Conclusion】 The phenotypic diversity of C. carlesii was the result of genetic and environmental factors. In addition, the variation in seeds was mainly influenced by longitude, annual mean temperature, and precipitation of the coldest quarter. The genetic variation within provenances was the main source of genetic variations of seed characteristics; therefore, the selection and utilization of superior individual plants should be strengthened in the genetic improvement of C. carlesii. JXDN has the characteristics of large seeds and high nutrition, and offers the potential for excellent provenances.
【Objective】 This study investigated the role of succession and regeneration for populations of Cyclocarya paliurus; in particular, seasonal dynamics of seed rain and soil seed bank characteristics were investigated.【Method】 Investigation of seasonal dynamics of seed rain was performed in plantations of C. paliurus with three densities (C1: 1 050 plant/hm2, C2: 720 plant/hm2, and C3: 525 plant/hm2), which were planted in Dashishan, Liyang, Jiangsu Province; the traits of seeds were also analyzed. In addition, we surveyed and dissected the soil seed banks dispersed in five natural populations located in Jiuling Mountain, Jiangxi Province. The soil seed banks in two layers, named as litter layer (Ⅰ) and soil layer (Ⅱ), were separately analyzed.【Result】 According to the density of seed rain, the duration of seed falling was divided into three stages: early stage (8.20-9.20), medium stage (9.20-12.10), and late stage (12.10-12.30); two peaks of seed rain were recorded at 9.10 and 12.20, respectively; the amount of seed rain during these two peaks in the early and late stage accounted for 42.4% and 43.5% of the whole annual production, respectively. The differences of seed rain and number of viable seeds at various stages were significant, but the other seed traits were insignificant. Moreover, the effects of plantation density on the number of full seeds and 1 000-seed weigh were significant, but no effect on the other seed traits was detected. In five natural populations of C. paliurus, the density of soil seed bank in the Ⅰ layer (37.4 grain/m2) was higher than that in the Ⅱ layer (17.9 grain/m2), and this parameter presented an obvious divergence among populations. Moreover, the seed diameter, thickness and volume from the Ⅱ layer were all smaller than those from the Ⅰ layer. More importantly, seed fullness and viability from the soil seed banks were lower by 13.0%-27.1% and 0%-10.4%, respectively. However, these indicators of seeds from the Ⅰ layer were generally higher those from the Ⅱ layer, indicating a descending tendency in seed quality as duration increases. 【Conclusion】 There were two peaks of seed rain in plantations of C. paliurus, and stand density affected the density of seed rain and 1 000-seed weigh more than seed fullness or viability. Both the quantity and quality of seeds in the soil banks from the Ⅰ layer were superior to those from the Ⅱ layer. The dormancy of seeds stored in soil is relieved in favor of regeneration and succession of C. paliurus populations.
【Objective】 In this study, experiments were carried out to explore the dynamic changes of nutrient contents, enzyme activities and endogenous hormones during the seed stratification of Phoebe sheareri. Additionally, this study was conducted to reveal the internal physiological mechanisms involved in seed dormancy and provide a theoretical basis for its dormancy release and germination. 【Method】 Fresh and full seeds of P. sheareri were treated with gibberellin and stratification was conducted; the physiological indicators during stratification were also determined. 【Result】 The seed dormancy of P. sheareri was relieved by stratification for 63 days. The germination rate of low temperature and variable temperature stratification was 85.83% and 72.75%, respectively. The initial starch content was 467.88 mg/g and decreased gradually during stratification. Soluble sugar, soluble protein and crude fat were decomposed to varying degrees. Under the two kinds of stratification treatments, the soluble sugar content in the seeds of P. sheareri changed greatly, from decreasing to increasing, and then decreasing again. The soluble protein content in P. sheareri seeds increased initially and then decreased under two stratification treatments. On the whole, the crude fat content in the seeds of P. sheareri showed a gradually decreasing trend under each stratification treatment. The activities of amylase, APA and POD were increased. This indicated that the two stratification treatments could promote the continuous activation of APA and POD activities. What’s more, endogenous hormones such as IAA, IPA, GA3 and ABA played an important role in the regulation of seed dormancy and germination. During the whole stratification process, the contents of IAA, IPA and GA3 increased, while the contents of ABA decreased, and the mass ratios of IAA/ABA, IPA/ABA and GA3/ABA increased. 【Conclusion】 There was medium dormancy in seeds of P. sheareri. Gibberellin and stratification could release dormancy, and cold stratification was better to accelerate seed germination. Starch was the main storage material in the seeds of P. sheareri. The transformation of nutrients and the coordination of endogenous hormones played an important role in the seeds dormancy release.
