| Lipids will be subject to geological processes including sedimentation and burial and will be preserved in geological settings after being released from their sources. Most geolipids were resistant to microbial degradation and keep the carbon skeletons of their precursors. Meanwhile, lipids may be influenced by temperature, humidity, salinity and pH etc. during diagenetic processes, which finally alter the distribution and compositions of lipids. Therefore, the geolipids in the sediments and rocks can not only reflect the biological sources, but also record the environment information while they are biosynthesized. The advantages of geolipids thus have been widely applied to reconstruct the paleoenvironment and paleoecology. However, the significance of lipids as paleoenvironmental indicators should be validated in the modern processes prior to their use in paleoenvironmental interpretation. Compared with the wide application of lipids in paleoenvironment reconstructions, less studies focus on the relationships between lipids from plants and their natural environment, especially on the long-term field monitoring.This dissertation will focus on two kinds of plants collected in Wuhan Botanical Garden monthly to explore the variation in the distribution of n-alkanes and their stable carbon isotope compositions. The two kinds of plants are composed of the Sinojackia genus as deciduous plant and the Osmanthus fragrans as an evergreen plant. The Sinojackia genus comprising 6 species, they are Sinojackia xylocarpa, S. microcarpa, S. sarcocarpa, S. oblongicarpa, S. huangmeiensis and S. dolichocaroa. Previous research has shown that S. dolichocaroa differs from other species in a number of ways, especially if flowers and fruits are considered, and it has been ascribed to an additional genus, Changiostyrax. So far, no chemicals studies have been carried out with Sinojackia genus. In this dissertation, we will analysis the n-alkanes distribution of the 6 Sinojackia species collected in different months and attempt to provide the chemical evidence for exploring this issue at the same time.In this study, the distribution of n-alkanes, the CPI and ACL values of n-alkanes and the stable carbon isotope compositions from the different species leaves, shade and sun leaves from the same plant and the epicuticular wax and the intracuticular wax from the same leaves which were all collected monthly will be discussed to explore the relationship the n-alkanes and the environmental factors. The Arabic gum is applied to separate the epicuticular wax and the intracuticular wax of the same leaves, and it is the first time to determinate the carbon isotopic compositions of n-alkanes which extracted from different layers of wax.By using the gas chromatography, gas chromatography mass spectrometer and gas chromatography-isotope ratio mass spectrometry to detect the distribution, concentration and carbon isotopic composition of n-alkanes from leaves, the results are summarized as follows:1) The carbon number distribution of n-alkanes from 6 Sinojackia species has not changed in different months (from April 2009 to April 2010). The range of the n-alkanes is between C23-C35, the distributions of n-alkanes show odd-even predominance (CPI> 10), with the C29, C31, C33 as the dominant components, the contents of odd carbon number n-alkanes are much higher than even carbon number n-alkanes, and this advantage did not change in the observation period. Values of average carbon chain length (ACL) of n-alkanes have been maintained at around 32 in the observation period, indicating they have longer carbon chain length of n-alkanes. CPI values of n-alkanes from the Sinojackia genus collected in different months gradually decrease from April 2009 to November 2009, but when it comes to the development of growth, such as in March and April 2010, the CPI values rises again to high values. The variation of the CPI values in the observation periods indicate that the young leaves have synthesized more odd carbon number n-alkanes/even carbon number n-alkanes than mature leaves. But the ACL values of n-alkanes have the opposite trend, they gradually increase during the observation period, and the nearly withered leaves have the highest values while the young leaves have the lowest values, which indicate the young leaves have synthesized less carbon chain length of n-alkanes than mature leaves. Based on the distribution of temperature and precipitation in the study area of the observed year, the environmental factors have less affected on the CPI and ACL values of n-alkanes, but the physiological processes of plant leaves has played an important role in the way of synthesizing n-alkanes.2) The carbon isotope composition of n-alkanes from leaves of the Sinojackia genus are between -31.4‰～41.7‰, which shows that they are typical C3 plants, although the carbon isotope composition of n-alkanes from leaves of the Sinojackia genus would change in different months, the Sinojackia genus has not changed its C3 photosynthetic pathways. The carbon isotope values of n-alkanes C29, C31, C33 gradually change with negative anomaly in the observation period between April 2009 to September 2009, and then they turn up to the relatively lightest in September and October 2009. Based on the distribution of temperature and precipitation in the study area of the observed year, the combined effect of temperature and precipitation variation may be the main reason of the carbon isotope composition of n-alkanes in the observation period.3) The carbon number distribution of n-alkanes from sun and shade leaves of the Osmanthus fragrans has not changed in different months. The range of the n-alkanes is between C23-C35, the distribution of n-alkanes shows odd-even predominance, with the C29, C31, C33 as the dominant components. The sun leaves have higher CPI values than the shade leaves, and they also have a more wider CPI variation than the latter. The differences of light intensity of the sun leaves and the shade leaves may affect the distribution of the n-alkanes between them. n-alkanes of the epicuticular wax has a higher CPI and ACL values than the intracuticular wax, which indicates that the epicuticular wax has an obvious odd carbon number n-alkanes/even carbon number n-alkanes predominance and longer average carbon length than the intracuticular wax. CPI values of n-alkanes from the epicuticular and intracuticular wax all gradually decreases, while the ACL values of n-alkanes from the epicuticular and intracuticular wax all gradually increases during the observed period. The variation of the CPI and ACL values of Osmanthus fragrans leaves are similar with the variation of CPI and ACL values of the Sinojackia genus in different months.4) The carbon isotope compositions of n-alkanes from sun leaves of Osmanthus fragrans are between-33.6%～-41.6‰, while the shade leaves have-34.9%‰～-41.2‰as the range for their carbon isotope compositions. The carbon isotope compositions of n-alkanes from epicuticular wax of Osmanthus fragrans are between-31.1‰～-39.1‰, while the carbon isotope compositions of n-alkanes from intracuticular wax of Osmanthus fragrans are between-31.8‰～-41.2%o. Comparison of the carbon isotope composition of n-alkanes from these sun and shade leaves and the epicuticular and intracuticular wax has showed that epicuticular wax has the heaviest n-alkanes carbon isotope compositions, the intracuticular wax has the lightest n-alkanes carbon isotope compositions. The epicuticular and intracuticular wax and sun leaves have the same trend in the variations of the n-alkanes of carbon isotope compositions, while the shade leaves have the opposite trend in the variations of the n-alkanes of carbon isotope compositions in the observed period.
|
PDF Full Text Request