Another methods paper by current and former members of our group. About how to properly dry the plant samples. It´s not as simple as you think…
Full citation: Portillo-Estrada, M., Copolovici, L., & Niinemets, Ü. (2015). Bias in leaf dry mass estimation after oven-drying isoprenoid-storing leaves. Trees, 1-12. (link to full text)
Foliage isoprenoid content or essential oil content is a key plant characteristic important in plant science, but also for food, cosmetic and pharmaceutical industry. Commonly, the amount of foliage chemicals is normalized with respect to leaf dry mass (content per dry mass). However, the protocols for foliage drying have received little attention. In particular, volatile and semi-volatile isoprenoids and other compounds with low boiling point may partly volatilize during drying, reducing both isoprenoid and leaf dry matter contents, thereby potentially underestimating the content of volatiles and overestimating that of non-volatile constituents. Three leaf preservation (flash freezing in liquid nitrogen, freezing at −82 and at −20 °C, and cooling at 4 °C) and two leaf desiccation (freeze-drying at −54 °C and 1.2 mbar, and air-drying at 30, 40 60, 70, 80, 100, 110, 125, 150, 200, and 300 °C) procedures were applied to replicate leaves, and the leaf dry matter content as well as the leaf isoprenoid content was measured afterwards. The results of this experiment suggested that freeze-drying method (FD) performed the best leaf isoprenoid preservation followed by FF method, whilst air-drying methods performed a dramatic isoprenoid loss in the leaf samples, as well as preserving the leaves at freezing and cooling temperatures. Leaf isoprenoid content and leaf dry to fresh mass ratio were correlated and there were evidences of leaf dry matter content (LDMC) miscalculation in isoprenoid-storing species when using traditional air-drying methods and preservation of samples, possibly related to the isoprenoid loss as well as other volatile compounds. In addition, losses of high C content volatiles and respiration of sugars and carbohydrate pyrolysis with low carbon content may differently affect the bulk leaf C content.