In the Philippines, where plants were collected only in Oct. (late wet season), the δ13C values of C3 plants were -29.5 ± 1.28 0, whereas those of C4 plants were -12.6 ± 1.110 . These results suggest that under an Asian Monsoon climate, C4 plants exhibit more neg. δ13C values in the dry season than in the wet season, whereas C3 plants as a whole show no clear seasonal changes in δ13C values.