For C and N determinations, leaves were ground to a homoge-
neous powder with an Eppendorf grinder (Retsch MM301), using
2 mL Eppendorf containers and 5-mm diameter glass balls. Prior to
analysis, the samples were dried at 70 ◦C for 24 h. Approximately
3 mg of sample was weighed into tin foil containers (2 mm × 5 mm)
and analyzed for C and N on a CHN elemental analyzer (Interscience
CE instruments, EA 11110 CHNS-O).