| Salix viminalis belongs Salix, Salicaceae, which is an important pioneer shrub species found in riparian environments. There are many excellent properties for S. viminalis, such as perennial habit, easy vegetative propagation, fast growth rate and good coppicing response. In recent years, S. viminalis is mainly used for bio-energy development, sewage sludge treatment, and phytoremediation of heavy metal contaminated soils, which has a promising prospect of application. The resource of S. viminalis is rich in our country, but related research work has not been carried out. In the past few decades, the survival of S. viminalis have been strongly impacted by human activities. and it is need of assessment and protection of this resource. S. viminalis is dioecious, and research of sexual differences can provide guidances for breeding and application. Thus, this study analyzed the genetic variance between and within populations, between and within sexual subpopulations, and evaluated the differences of heat resistance and differences of growth and defense under different growth stages for male and female plants of S. viminalis. This study was to supply theoretical basis for genetic improvement and germplasm conserving of S. viminalis, and provide a reference for selective use of male and female plants in S. viminalis. The main results are as follows:1. The genetic variance of 12 populations of S. viminalis across Ergun basin and West Liao basin were analyzed using 20 microsatellite markers. The results indicated a high level of genetic diversity(Na=16.45, He=0.7416) and moderate population differentiation(FST=0.0761) in S. viminalis. The 12 populations could be divided into two clusters by Bayesian analysis, Neighbor-Joining clustering and Principle Coordinates Analysis(PCo A), and the two clusters conformed to that populations derived from two basins. Significant correlations of Nei’s genetic distance and FST/(1-FST) with log(geographic distance)(r=0.4398, p<0.00; r=0.4029, p<0.00) indicated that geographical distance was the principal factor influencing genetic structure. Moreover, the differentiation of the three populations with short distance(1.5~1.9 km) from Zhadun river was very low. AMOVA showed most of genetic variation(86.13%) was attributed to individual differences within populations, while 11.49% was ascribed to differences of two basins and 2.38% existed in populations within each basin. Populations from Ergun basin exhibited higher genetic diversity and higher number of private alleles than that from West Liao basin, especially TL, MDG2, ZD1 and GH. The aforementioned populations are important reservoirs of genetic variation for special germplasm resources and they deserve to be given high priority for protection.2. The genetic variance of 5 pairs of sexual subpopulations of S. viminalis across Ergun basin and West Liao basin were analyzed using the above 20 microsatellite markers. No statistically significant difference was detected between male and female subpopulations by paired-sample t test, but the average genetic diversity of male subpopulations(Na=7.12, He=0.7071) and female subpopulations(Na=7.31, He=0.7226) were high. Moreover, there was no difference in genetic diversity between male and female subpopulations under unfavorable environments(West Liao basin). The differentiation of the ten subpopulations in S. viminalis was moderate(FST=0.0858), which was conformed by AMOVA that most of genetic variance(94%) existed within subpopulations. Pairwise FST indicated no differentiation between sexual subpopulations, which was accompanied by high long-term migrate between them(M=0.73~1.26). However, little recent migration was found between sexual subpopulations. Therefore, artificial crossing or/and transplantation by cutting propagation should be carried out so as to increase the migration during the process of in situ conservation.3. Most of physiological traits of male and female plants of S. viminalis showed no significant differences under normal condition. After 7 days stressed by 40 ℃/30 ℃(day temperature/ night temperature), the net photosynthetic rate(Pn) of males and females declined 44.84 % and 54.43 % respectively, but the Pn of males were significantly higher than females. Sexual differences in Pn was mainly due to non-stomatal limitation: the activities of 1, 5-bishosphate carboxylase ribulose(Rubisco) of males and females decreased by 31.52% and 39.71 % separately, and the activities of males was significantly higher than that of females. Under high temperature stress, the actual photochemical efficiency((37)PSII) and relative electron transport rate(r ETR) decreased significantly, but(37)PSII and r ETR of males were significantly higher than these of females; photochemical quenching coefficient(q P) and regulatory energy dissipation [Y(NPQ)] did not change significantly, non-photochemical quenching coefficient(q N) decreased significantly and non-regulatory energy dissipation [Y(NO)] increased significantly. After 7 days stressed by high temperature, q P, q N and Y(NPQ) of males were significantly higher than those of females, while Y(NO) of females was significantly higher than that of males. Carotenoid(Car) contents increased significantly, and the content of males was significantly higher than that of females. EC value and O2- production rate increased significantly, but they were significantly higher in female plants than in male plants. The activities of superoxide dismutase(SOD), catalase(CAT) and ascorbate peroxidase(As A-POD) went up significantly, the activity of peroxidase(POD) declined markedly, but the activities of the four enzymes in male plants were significantly higher than those in female plants. Proline(Pro) and solute protein(SP) contents rose significantly, but their contents in male plants were significantly higher than in female plants. According above results, the damage of females was more serious, while males possessed more stronger protective capability and can better adapt for heat environment. Under high temperature, the mean differentiation coefficient(VST) was 21.69 % indicated the differentiation of males and females was small and 78.31 % of variation was within clones. Abundant variations exist in S. viminalis clones, yet male plants possess more strongly regulated and adaptive ability under high temperature stress. Thus, to obtain heat-resistance germplasm, male plants should be selected in future breeding project of S. viminalis.4. We studied growth and defense differences of male and female plants of S. viminalis under different growth stages. At June, the plant height and ground diameter of males and females showed no significantly differences; at July, the plant height of males were significantly higher than that of females, while the ground diameter of males and females showed no significantly differences; during August and October, the plant height and ground diameter of males were significantly higher than these of females. Sexual differences in growth could be explained by differences in photosynthesis: at June, the Pn of males and females were not significantly different; during July and October, the Pn of males were significantly higher than that of females. No sexual differences in stomatal conductance(Gs) and intercellular CO2 concentration(Ci) indicated the sexual difference in Pn was due to non-stomatal limitation. At June, chlorophyll a(chl a), chlorophyll b(chl b), and carotenoid(Car) contents showed no significant differences between male and female plants; during July and October, the contents of three photosynthetic pigments were significantly higher in males than in females, so sexual difference of photosynthetic pigments was one reason of sexual difference in photosynthesis. During June and October, the contents of polyphenol and tannin showed no differences in male and female plants. At June, the activities of SOD and phenylalanine ammonialyase(PAL) showed no differences between males and females, while the activities of POD and polyphenol oxidase(PPO) were significantly higher than in males than in females; during July and October, the activities of the four enzymes were significantly higher in males than in females, which indicated the defense ability was stronger in males than females. According to the above results, we could find that sexual differences were stable between July and October. The growth was more quicker and the defense was more stronger in males, which could make up the shortage of males in natural populations, thus sustaining the stability of S. viminalis.In conclusion, most of genetic variance and physiological variance exist in clones. Considering that the growth was quicker, the defense was stronger and the heat resistance ability was also stronger in males, so selecting more males contribute to obtain newgermplasms with excellent growth and resistance. |
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