Collection and elemental content measurement of leaf litter
We examined 11 tree species commonly found in the mountainous areas of northeast Japan. Among these species, we examined both young and aged leaf litter of oak (Quercus serrata ). Thus, we examined a total of 12 types of leaf litter. These shed leaves were collected at Zao (N38.122, E140.451) on October 3, 2020, at Kawatabi (N38.745, E140.757) on October 15, 2020, and at Aobayama (N38.259, E140.837) on November 19, 2020 in Miyagi Prefecture, Japan (Table 1). All leaves were collected within a week of falling on other leaf litter on the ground, and therefore did not directly come into direct contact with the soil.
The leaf litter was dried at room temperature (approximately 20 °C) in paper bags until it was used for measuring its C, N, and P contents. Prior to experiment, the C and N contents in the leaf litter were measured using an elemental analyzer (2400 Series II CHNS/O Analyzer, Perkin Elmer, Shelton, Connecticut). For estimating the P content in the leaf litter, the weighed amount of dry leaf litter was first combusted (420 °C) for 2 h to turn the litter into ash, which was suspended in 10 mL of distilled water. The mixture of ashes and distilled water was autoclaved with potassium persulfate for 30 min to oxidize organic phosphorus compounds and the total orthophosphate concentration was measured by ascorbate-reduced molybdenum blue method (Murphy and Riley 1962, Menzel and Corwin 1965).