Understanding the disparity in climate resilience among angiosperms and gymnosperms from the higher Himalayas: Inferences drawn from lipid biomarkers using a Machine Learning approach

The relative abundances of n-alkanes and fatty acids in plant-derived organic matter serve as reliable biomarkers in paleoecological studies, given that leaf wax characterisation in terrestrial plants is a function of the external environment. Owing to limited phylogenetic and geographic sampling in earlier studies, the relative weight of environmental factors and plant phylogeny on leaf wax production is yet to be well constrained. Here, we try to address the gap in the geographical and botanical representation of terrestrial plants and explain their inherent disparity in lipid composition as a function of environment and phylogeny. To do so, we examined 13 plant species, ranging 500-5200 m altitude, from the northwest to eastern Himalayas, covering three countries, contrasting climate, diverse forest types, over three years. We report: (a) Juniperus (gymnosperm) produces twice the amount of n-alkanes as compared to the coexisting angiosperms; (b) gymnosperm fatty acid concentration is several times higher above the snowline (3000 m) than below due to moisture stress and stronger solar influx; (c) angiosperms fatty acid abundance mimics the precipitation bands in the Himalayas at 2000 m and 4000 m altitude; and (d) the response of plant physiology to climatic forcings is observed in Rhododendron where n-alkane production is connected to the timing of flowering and seed-ripening.

We applied a Machine Learning (ML) classifier built on Principal Component Analysis and Logistic Regression to disentangle a plant's phylogenetic signal from its external environment. Using ML-based classification, we established the linkage between a plant's phylogenetic signal with its external environment and internal traits such as the production of leaf wax. We propose that the production of n-alkanes in the leaf wax of plants is primarily determined by the plant's phylogenetic signal rather than its external environment. Over a longer geological time scale, persistent climate forcings are eventually registered in the plant's genetic information, but at shorter (annual to decadal) scales, as represented by plant individuals, the climatic signal is secondary as far as the plant's lipid production is concerned.