Abstract: The photosynthetic rate, transpiration rate, daily CO₂ assimilation quantity and water use efficiency of Pinus massoniana, Pinus elliottii and Pinus caribaea in hilly regions of south subtropics of Guangdong were measured. The photosynthetic and transpiration rate of test pines displayed daily and seasonal variations,with the maximum in summer and the minimum in winter. Among the test pines, P.caribaca had the highest annual average daily CO₂ assimilation and water use efficiency,indicating that is more adaptive to the local environment,and should be widely popularized in this study area.

Key words: Pine, Photosynthetic rate, Transpiration rate, Water use efficiency, evolution law, hydrological variability, inheritance theory, inconsistent., hydrological gene, principle of hydrology