Understanding the Distribution of n-alkane and n-alkanoic acid in High Mountain Vegetation: A Case Study from the Himalayan Mountain Forest

Prakash, Puncet (2022) Understanding the Distribution of n-alkane and n-alkanoic acid in High Mountain Vegetation: A Case Study from the Himalayan Mountain Forest. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Puneet Prakash (15MS075)) 15MS075_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The lipid components of the protective waxes that cover the leaf surfaces of practically all land plants are environmentally persistent. They are typically constituted of 24–36 carbon atoms long, straight-chain (i.e., normal, n-) alkanes, alkanols, and alkanoic acids. The alkanes are predominant of odd carbon numbers and the alkanols and alkanoic acids are of even carbon numbers. The elimination of a single carbon from the precursor even-numbered n-alkanoic acids yields the odd-numbered n-alkanes. They are ideal biomarker molecules because of their aqueous solubility, low volatility (for molecules with more than 20 carbon atoms), chemical inertness, and resistance to biological degradation. Thus, lipid distribution is a function of environmental variables and can be used to examine climate- plant relationships in the modern environment as well as the paleoenvironment using sedimentary records. The Himalayan biosphere has diverse types of vegetation spreading across different climatic conditions, so we can analyze the variation of n-alkane and n-alkanoic acid (FAME/FAs) concentrations within the different plant groups, majorly angiosperm and gymnosperms, with factors such as elevation, temperature, and precipitation. To check this, we calculated the carbon preference index (CPI), average chain length (ACL) and total alkane and FAs concentration from the leaf sample of modern plants (n=81). We collected the leaf sample from the Sikkim and the upper West Bengal region of the Eastern Himalayas. We found that the n-alkane concentration in gymnosperm plants is more than in angiosperm plants, whereas FAs concentration in angiosperm plants is more than in gymnosperm plants. For n-alkane, the average ACL value is 30 for angiosperm and for gymnosperm it is 32. In FAs, we get an ACL value of 27 for angiosperm and gymnosperm. There is a good positive correlation between the CPI value and n-alkane concentration. In angiosperm, CPI value for alkane is 13 and 6 for FAs, whereas for gymnosperm it is 10 and 6 for alkane and FAs, respectively. In angiosperm, there is a two- peak concentration pattern with increase in elevation, while in gymnosperm n-alkane and FAs concentration increases with elevation. We propose species-level control at elevation specific biomes occurring at different altitudes along the transect for this kind of observation. In angiosperm, the n-alkane concentration decreases with an increase in temperature, whereas in n-alkane and FAs, it is decreasing. The Himalayan example adds fresh findings to our knowledge on mountain ecosystems equating long-chain n-alkane distribution in higher plants with climatic and topographical drivers, thereby enabling us to differentiate montane geographies and climatic niches from lowland regions.

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