| Phoebe zhennan is subtropical evergreen broad-leaved tall tree of Lauraceae Phoebe, national key protected species, common in the broad-leaved forests below 1500 m elevation in south China, known as "gold in wood ". P.zhennan mainly distribute in the west of Hubei, northwest of Guizhou, Sichuan and Chongqing. The reason of its high value is resourse scarcity because of long-time logging, slow growth, and immature cultivation technology, led to its plantation is far from cut for utilization. In recent years, with the government support for the development of rare tree species, the studies on P.zhennan are gradually increasing. Under the impact of resource scarcity and the great attention of government, the relative organizations of government has paied great attention on the cultivation work, researches on germplasm resources’ genetic diversity and improvements on seedling cultivation technology are pressing to economic development of modern forestry. Previous studies mostly have related to the growth pattern, resource protection, exploitation and seedling cultivation of P.zhennan, however, studies are still blank on the germplasm resource, growth characteristics, nutrition regulation and dynamic physiology, environmental stress and physiological response and other aspects.We collected P.zhennan from mainly distributions in China, including Sichuan, (35), Yunnan (3), Chongqing (13), Guizhou (10), Hubei (14) and Hunan (17), totally 6 Province,49 counties, used AFLP molecular marker technique to scan the whole genome of 92 samples. Seeds for Polyembryonic study were collected from ya’an Yucheng District and Dujiangyan 4 age classes 3 stands,8 trees. Seeds of mother trees are divided into large, medium and small three categories,24 materials in total. The growth and photosynthetic physiological characteristics of 6th mother tree were observed. Selecting nitrogen (NF), compound fertilizer (CF), organic fertilizer (OF) and mixed fertilizer (MF) and setting control (CK), low, medium and high fertilization levels to perform a pot experiment on P.zhennan. Fertilizers were evenly applied into corresponding planting bucket in March, May, July of 2013,2014, photosynthetic physiology and growth indices were measured in August. April to May in 2014, P.zhennan which were substantially consistent were selected to perform persistent drought 0 (normal supply),5,10,15,20,25 and 30 d, correspondingly denoted as DO (CK), D5, D10, D15, D20, D25 and D30, each dealing with three repeat. At the beginning and end of drought stress, morphological and photosynthetic physiological indicators were measured. Normal watering after stress, main photosynthetic parameters were measured after 5 and 10 d. The main findings were as follows:(1) Bayesian assignment test, cluster analysis and principal component analysis indicated that P. zhennan in this study could be divided into three genetic populations, SCZ, CQH and YG The CQH could further diverged into two geographical populations:CD-CQ and HB-HN. Selectively amplified results of 12 primer combinations for 92 individuals were analyzed and produced 422 bands in total, with 40.4%(177 loci) were polymorphic. The inferred population with greatest percent polymorphism (31.8%) was CD-CQ, while percent polymorphism of SCZ and YG were both low (16.2%,16.1% respectively). The average genetic diversity of all populations was 0.1163, while CD-CQ had the largest value of 0.1676 and SCZ had the lowest value of 0.0745. The genetic distance between SCZ and YG was the highest (0.1284), between CD-CQ and HB-HN was the lowest (0.0241). Pairwise OPT between any inferred populations were significant (P<0.001), and the largest ΦPT value (0.678) existed between SCZ and YG, with the lowest value (0.257) between CD-CQ and HB-HN. The Mantel test revealed a positive correlation between genetic differentiation and geographical distance among the four inferred P. zhennan populations.(2) Polyembryony existed in 8 strains of P. zhennan seeds from different mother trees, the polyembryonic rate was up to 56.3%(No.7,150-year-old), and lowest to 4.3%(No.8,80-year-old), with the highest rate in double embryos, followed by three embryos, lowest in four embryos. Polyembryonic rate was not significant between different size fractions of seeds, or changed regularly as the age of mother trees increased. Observation of the offspring with the highest polyembryonic rate showed that:average height and ground diameter of big one in double embryos (SD) were 12.71 cm and 2.13 mm, with little difference to single embryo (D), while, the small one in double embryos (SX) were just 1/2 of D. Observations to polyembryony (1-year-old) of healthy mother trees which are in full fruit period showed that:at the beginning of transplanting (2 months later), net photosynthetic rate (Pn) and gas exchange parameters, light response and CO2 response curve of SD were at the same level with D, while Pw and gas exchange rate of SX were inhibited, as the light intensity and CO2 concentration increased the rising ranges of the two response curves were small; at the end of transplanting (4 months later), photosynthetic capacity of SX was improved. But 7 months later, the height and ground diameter of SX were still far worse than SD.(3) P. zhennan treated with organic fertilizer (OF) and mixed fertilizer (MF) showed a larger height and ground diameter increment than nitrogen fertilizer (NF) and compound fertilizer (CF), with no big differences among NF, CF and MF fertilization levels respectively.While, the growth increment of P. zhennan under OF treatment first increased then dropped as the fertilizer amount raised, even up to 2 times of CK in medium level of OF (MOF).Secondly, all of the four different fertilizers could promote chlorophyll (Chi) synthesis, reduce carotenoid (Car) content, increase Pn and gas exchange parameters of P. zhennan, with better effect in OF and MF, and best effect in MOF.In addition, after the four kinds of fertilizers were applied into soil respectively, light response and CO2 response curves of P. zhennan leaves ascended (greater rate of increase in OF and MF), meanwhile, leaf light saturation point (LSP) and CO2 saturation point (CSP) elevated accompanied by light compensation point (LCP) and CO2 compensation point (CCP) reduced under Mof treatment.(4) Drought stress caused severely inhibitition in height and diameter growth of P. zhennan, and a heavy drought even lead shrinkage of the stem and leaf curling. With the extension of drought time, soil water content (SWC) of P. zhennan leaves decreased significantly, SWC of normal water supply (DO) was about 20%, dropped to 9%after 5 d. As the severity of the drought aggravated, leaf relative water content (LRWC) of P. zhennan leaves gradually decreased, dropped to half of DO under severe drought, Chi content first rose then reduced, Car content were significantly decreased under D30 treatment, decline extent of Pn, Gs, Tr gradually increased, water use efficiency (WUE) plunged to about 7% of DO (severe drought), the light response and CO2 response curves gradually smooth, AQY, CE, Pn max and LSP decreased, LCP and CCP slightly escalated. Photosynthetic diurnal variation of P. zhennan leaves was "single peak" curve, drought stress resulted in the peak time of Pn appeared from 12:00 to 10:00 in advance, and with the drought stress intensified, the peak gradually disappeared. After rehydration,Pn Gs, Tr of P. zhennan leaves under all treatments were increased to varying degrees. Besides, with the extension of rehydration time (10 d), WUE increased, which soared to 10.0 under D30 treatment.In summary, from the point of construction of P. zhennan germplasm gene bank, gene exchange between CD-CQ and HB-HN should be strengthened. In practical, high multi-embryo may adverse to seedling growth. But after one year cultivation, the big one in double embryo may catch with single embryo, while part of the small one may be qualified through intensive cultivation. Undoubtedly, this will increase cultivation cost, therefore, the elimination of small ones is reasonable in practice. OF application can provide nutrients effectively, application OF on the basis of NF can be used as one timely improvement. In addition, reasonable water management measures should be developed for P. zhennan, in case that severe drought for a long time (ie, SWC less than 6%) cause irreversible damage to P. zhennan. |
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