• C3 plants;
  • C4 plants;
  • natural 13C abundance;
  • Thailand;
  • the Philippines


The natural 13C abundance (δ13C) of plant leaves collected from fields in Thailand and the Philippines (Asian Monsoon tropics) was analyzed, and changes in the δ13C values of C3 and C4 plants in wet and dry seasons were characterized. In Thailand, the δ13C values of C3 plants were −29.2 ± 1.04 (mean ± standard deviation) ‰ in July and August (wet season) and −28.6 ± 1.05‰ in February and March (dry season): these values are not significantly different, whereas the values of C4 plants were −12.7 ± 0.56‰ in the wet season and −14.5 ± 0.68‰ in the dry season (P < 0.01, t-test). In the Philippines, where plants were collected only in October (late wet season), the δ13C values of C3 plants were −29.5 ± 1.28‰, whereas those of C4 plants were −12.6 ± 1.11‰. These results suggest that under an Asian Monsoon climate, C4 plants exhibit more negative 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.