Leaf morphology and stable isotope ratios of carbon and nitrogen in Acacia senegal (L.) Wild trees vary with climate at the geographic origin and ploidy level

Leaf morphology, total leaf nitrogen (N) content and carbon and nitrogen isotope ratios of Acacia senegal trees vary among ploidy levels and geographic origins. Leaf morphology was significantly correlated with carbon isotope composition (δ13C) among diploid trees, while a significant correlation was observed with nitrogen isotope composition (δ15N) among tetraploid trees. Leaf morphology and ploidy level can influence plants' ability to adapt to climatic conditions. Here we study Acacia senegal that has multiple ploidy levels and grows across a geographic range of mainly dry environments. We test if and how ploidy level and climate at the site of origin influence leaf shape and ratios of stable carbon and nitrogen isotopes of A. senegal. The study is based on leaves collected from 225 A. senegal trees representing 16 populations across the species range, grown in a common garden trial in Senegal. Leaf morphological parameters were measured, and ploidy level, total leaf nitrogen (N), carbon isotope ratios (δ13C) and nitrogen isotope ratios (δ15N) were determined. Three levels of ploidy were found, namely diploid, triploid and tetraploid, but at highly different frequencies among the 16 origins. Leaf morphology varied significantly among both geographic origins and ploidy levels, with especially triploid trees having distinct leaf shapes. Tetraploids displayed high δ13C and low δ15N values compared to diploids. For diploids, leaf length and number of leaflets were correlated with precipitation and latitude, respectively. Leaf morphology and isotopic discrimination in A. senegal vary according to ploidy level and geographic origin. Our analysis suggests that the differences likely reflect adaptation to different environments, but the patterns tend to differ between diploids and tetraploids.