Finnigan delta plus xptm

For ¹³C/¹²C analysis, samples (0.06 mg) were packed in tin capsules and then combusted in an Elemental Analyzer (Flash EA^TM 1112, Thermo Scientific, Bremen, Germany). The CO₂ evolving from flash combustion of the samples (in the presence of O₂ at a temperature of 900°C) was flushed into an isotope ratio mass spectrometer (Finnigan Delta Plus XP^TM, Thermo Scientific, Bremen, Germany). For ¹⁸O/¹⁶O analysis, samples (0.06 mg) were packed in silver capsules and dropped into a pyrolyser (Finnigan TC/EA^TM, Thermo Scientific, Bremen, Germany), where the CO₂ and H₂ produced at a temperature of 1450°C without oxygen were sent to a gas chromatography column and then to the mass spectrometer. Isotopic composition was denoted using the standard delta notation (δ, ‰):δ(‰) = R_sample/R_stand – 1, where R_sample and R_stand were isotopic ratios in samples and standards, respectively. Carbon and oxygen standards were Vienna Pee Dee Belemnite and Vienna Mean Ocean Water.

Fully expanded leaves in plots were selected, oven-dried at 60°C to constant weight, ground, and sieved through a 250 μm screen. Leaf powder (0.06 mg) was packed in tin capsules, which were sealed and measured using an Elemental Analyzer (FlashEATM 1112, ThermoScientific, Germany) coupled with an isotope ratio mass spectrometer (Finnigan Delta Plus XPTM, ThermoScientific). Stable C and N isotope compositions were expressed using standard delta notation: (δ, ‰) = Rsample/Rstandard - 1, where Rsample and Rstandard were isotopic ratios in samples and standards, respectively. Total N and C in leaf powders were also measured using an elemental analyzer (VarioMACRO cube).