| Phoebe Zhennan S.Lee is a unique tree species in China that is Excellent features of producing high quality timber and shares high esthetic and economic values.But long time over-exploitation has almost depleted the abundance of this precious species,lack of seedling resources,immaturity in seedlings production,and the slow growth rate of the plant itself have been limitation to the development of artificial forest of P.Zhennan.Although previous studies have involved the influence of the growth of P.Zhennan by polyembryony and application of fertilizers,no data has yet shown the correlation between seed polyembryony,germination rate,polyembryonate properties and seed tree and seed size;moreover,the impact of the application of fertilizers on the growth of polyembryonate seedlings has not been reported.Therefore,this research provided a theoretical foundation and technical reference to the promotion of seedling cultivation,enhancement of the availability of improved variety,and the development of artificial forest of P.Zhennan.The performance of our study was described as follows:? Three populations of P.Zhennan from different locations in the lower hilly region of western Sichuan basin were chosen as the seed trees in November 2013.? In May 2014,nutritional bags were used to cultivate the seedlings aged 45 d(preliminary lignification found in roots and shoots).Mono seedlings(D),large double seedlings(SD),and small double seedlings of P.Zhennan were planted in bags and divided into 3 groups according to 3 different fertilization levels which included Medium(M,0.2 g per bag),High(H,0.3 g per bag)and a control(CK,0 g per bag,on the basis of the quantity of annual application of compound fertilizer).The application of fertilizers began at July,in which fertilizer was applied 4 times(25%for each application)at a 20 d interval and the influence on the growth of polyembryonate seedlings and photosynthetic physiology by the application of fertilizer was determined by measuring the growth and photosynthetic physiological indices.? In December 2015,seedlings of different fertilization treatments were transferred to large pots for regular management and the observation on the growth of polyembryonate seedlings revealed that:(1)The germination rate of the individual seed tree of P.Zhennan amounted to 92.33%but no significant statistical difference was found in the relationship between the seed tree and seed size.(2)No significant difference was found in the polyembryony rate of seeds of different size fraction from the same seed tree.Obvious correlation was not observed in the polyembryony rate of seed trees of different ages from the same population,which indicated the polyembryony rate had no apparent bearings on the tree age and vise versa.(3)Polyembryony was found to be existent between different seed trees,of which the highest was 60.00%and the lowest 6.33%,though the rate was not the same.Apart from the mono seedlings,the number of double seedling plants was the highest,the triple seedlings third,and the quad-seedlings lowest.It was concluded that polyembryony was closely related to the seed tree individuals due to the significant difference in double,triple and quad-seedlings of different seed plants.(4)The choice of seeds of medium to large size from the seed trees in the culture of P.Zhennan seedlings could help increase the number and quality of the qualified nursery stock.The fact that the seedling height,ground diameter,total weight of roots,shoots of mono seedlings were significantly higher than that of polyembryonate seedling showed an influence was exerted by the seed quality and polyembryony rate on the successful cultivation of P.Zhennan seedlings.(5)Medium level fertilization(M)showed a significant promoting effect on the height and ground diameter of the seedlings in category 3,while high level fertilization(H)increase the seedling growth at first and then showed inhibitory effects afterwards in the whole experimentation.(6)Medium level fertilization facilitated the synthesis of chlorophyll of the leaves of category 3 seedlings,prolonged the functional period of the leaves,and increased net photosynthetic rate and stomatal conductance,which accounted for the enhanced photosynthesis under conditions of high illumination and CO2.(7)Moderate fertilization(M)resulted in the reduction of light compensation point(LCP),carbon dioxide compensation point(CCP),and the increase of photo-quantum efficiency(AQY),RuBP carboxylic efficiency(CE),dark respiration rate(RD),photorespiration rate(Resp),light saturation point(LSP),CO2 saturation point(CSP),and together with the adaptability of seedlings to environment leading to more accumulation of organic matter.High fertilization(H)also caused a promotion in seedling photosynthetic indices and followed by an inhibitory effect.It was shown that moderate fertilization could enhance the synthesis of photosynthetic pigments,photosynthetic efficiency,and the environmental adaptability in the seedlings of P.Zhennan,and thereby,the growth of the seedlings was promoted.Moderate fertilization(M)could also help narrow the gap between the growth indices of large double seedlings and single seedlings while stimulating the growth of small double seedlings,which is of vital importance to the promotion of the protection,the successful cultivation,and reducing the nursery of this precious tree species.(8)The polyembryonic seedlings of the annual P.Zhennan was transferred to large pots for a yearlong regular management and continuous observation.It was shown that moderate fertilization(M)still increased the seedling growth after the transfer,however,high nitrogen fertilizer-treated groups(D and SD)exhibited improved growth probably due to the alleviation of the inhibitory effects caused by overdose fertilization but no significant difference was found afterwards in the comparison with the fast growing control group(CK)after the transfer.The morphological and photosynthetic indices of SD and D did not exhibit significant difference,which was even further reduced for SX and D.The observation of the growth conditions of the polyembryonate seedlings after seedling nursery could help further understand the influence of fertilization on the growth of polyembryonate seedlings and will be of great significance to the studies of the variation trend of them in the later phase of the growth. |
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