Background and Aims Phytoremediation is an important method for restoring bare soil or slag; however, the physiological traits of plants used for revegetation are poorly known, even though such traits are important to successful remediation. This study was carried out on oil shale waste in Maoming City, Guangdong Province to screen for tree species with high photosynthetic potential, appraise the ability of these plants to acclimatize to oil shale waste, and provide valuable information for ecological restoration of similar waste sites.
Methods Diurnal variation of photosynthesis was measured for 12 tree species in summer and winter, using portable photosynthetic equipment (LI-6400, LI-COR, Inc., USA). Other parameters such as transpiration, stomatal conductance, relative humidity, etc. were measured simultaneously, and water use efficiency (WUE) was calculated as net photosynthesis divided by transpiration.
Key Results There were large seasonal differences in all parameters, with values of net photosynthesis, transpiration, and stomatal conductance higher in summer than winter (60.9%, 77.7% and 85.7%, respectively), but WUE higher in winter than in summer (26.8%-77.2%). Diurnal variation of net photosynthesis also exhibited seasonal differences. Many tree species exhibited a bimodal peak in summer and a unimodal peak in winter; however, Cinnamomum camphora was unimodal in both seasons; Terminalia bellirica, Tristania confertam, and Tectona grandis were bimodal in both seasons; and Syzygium cumini was bimodal in winter and unimodal in summer. Trees with higher mean net photosynthetic rate in both winter and in summer should be more useful for phytoremediation than species with high net photosynthetic rate in only one season. Accordingly, net photosynthetic rate, which synthesizes all parameters examined, should be considered the most important parameter to appraise the ability of plants to acclimatize.
Conclusions According to mean net photosynthetic rates in both winter and summer, the sequence of photosynthesis efficiency of the 12 tree species tested was: Acacia auriculiformis, Terminalia bellirica, Cassia siamea, Gmelina arborea, Tectona grandis, Tristania conferta, Cinnamomum camphora, Ormosia pinnata, Ilex rotunda, Syzygium cumini, Peltophorum ptetocarpum and Pterygota alata.