Effects of drying methods on plant lipid compounds and bulk isotopic compositions

Plant lipid biomarkers, such as plant waxes and terpenoids, and the stable isotopic composition of bulk leaves are widely used in both modern and paleoclimate studies for tracking vegetation and climate. However, the effects of different drying methods on the preservation of plant lipid biomarkers and the stable isotopic compositions of leaves are less explored. Here, we investigated various drying methods for the measurement of plant lipid concentrations and bulk leaf isotopic compositions.

Leaves from four tree species (Acer rubrum, Pinus sylvestris, Platanus occidentalis, and Taxodium distichum) were collected and dried using air, an oven, a freeze-dryer, and a microwave. We compared concentrations of leaf waxes and terpenoids and carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotopic compositions of leaves by different drying methods.

The air, oven, freeze-dryer, and microwave drying methods did not affect lipid concentrations significantly, and only a few homologues differed (38.1% or 41.8 μg/g on average) possibly due to biological variations or enhanced extraction efficiencies. The δ¹³ C values were not affected by drying methods, whereas the δ¹⁵ N values in oven-dried leaves in some species were higher by 0.2-0.7‰ than those obtained by other methods. Though small, we attribute these patterns to loss of leaf compounds with lower isotope ratios during oven-drying.

Based on our results, each drying technique yielded equivalent results for all plant wax and terpenoid concentrations and bulk leaf δ¹³ C values; however, oven-drying modified the δ¹⁵ N values.