The natural occurrence and altitudinal pattern of species with C4 photosynthesis were investigated on Qinghai Plateau, Qinghai province by using stable carbon isotopes in plant leaves and using additional data from references. A total of 58 species belonging to 10 families and 34 genera were identified using C4 photosynthetic pathway, which is only 1.66 % of total 3 500 plant species in Qinghai province. The leading two families, i.e. Gramineae (23 species) and Chenopodiaceae (22 species) contain 77.6 % of all C4 plants in the studied area. The number of C4 species increased from 1 600 to 2 400 m a.s.l. and then decreases quickly till 4 400 m a.s.l. with one half of C4 species distributing from 2 200 to 2 800 m a.s.l. (48 %). Eight plant species were found above 4 000 m a.s.l., but the distribution of these species is limited to the south of Qinghai province (low latitude area) where annual mean temperature is above 0 °C, suggesting that low temperature may generally limit the distribution of C4 plants. and M. C. Li, J. J. Zhu, L. X. Li
C4 photosynthetic pathway and life form were determined for 159 species in 71 genera and 13 families in the grassland of North China. 45 % of the C4 species were found in Graminae, 19 % in each of Cyperaceae and Chenopodiaceae. More than 51 % of these C4 species were in therophyta and 36 % hemicryptophyta, while fewer species were in nanophanerophyta (9 %) or geophyta (5 %). The numbers of C4 species and their life forms were closely related with grassland deterioration and succession in North China. This indicated that the C4 species had greater capacity to tolerate environmental stress (e.g. drought and salinity) caused by animal grazing and cultivation.