Leaf margin analysis of Chinese woody plants and the constraints on its application to palaeoclimatic reconstruction

Aim: Leaf margin states have been found to be strongly related to temperature, and hence have been used to reconstruct palaeotemperatures. Here, we aimed to explore the uncertainties and conditions of use of this technique in China by testing the influences of plant life-form, precipitation and evolutionary history on the relationship between percentage of untoothed species and temperature. Location: China. Methods: Using distribution maps and leaf margin states (untoothed versus toothed) of 10,480 Chinese woody dicots and dated family-level phylogenies, we evaluated the phylogenetic signal of leaf margin state, and demonstrated the variation in the patterns of leaf margin percentage and the relationship with temperature across different life-forms (evergreen and deciduous; trees, shrubs and lianas), regions with different precipitation and species quartiles with different family ages. Results: Significant phylogenetic signals were found for the percentage of untoothed species within families. Relationships between leaf margin percentage and temperature were: (1) weak or insignificant for all woody dicots, shrubs, evergreen and deciduous dicots, but strong for trees and lianas; (2) significantly enhanced with increasing precipitation, and (3) significantly weakened for trees belonging to old families. Main conclusions: Our results showed the complete leaf margin spectrum found in China and revealed great uncertainties in its relationship with temperature induced by life-form, precipitation and evolutionary history. These findings suggest that analysis of leaf margins for palaeotemperature reconstruction should be done cautiously: (1) only dicot trees with a relatively young family age can be used and their leaf margin states are more strongly affected by winter cold than by mean annual temperature; (2) the transfer function between leaf margin percentage and temperature is only reliable in humid and semi-humid regions of China.