Abstract：With CIRAS-2 portable photosynthesis system, diurnal variations and response to light of gas exchange parameters of clove (Syringa oblata Lindl.) leaf in four years old were studied under different soil moisture content in the loess hilly region in semi-arid area. The results indicated the Photosynthetic rate(Pn), Transpiration rate(Tr), Water Use Efficiency of Leaf(WUE), Stomatal conductance(Gs) and Intercelluar CO2 concentration (C i) had clear threshold value responses to soil moisture and Photosynthetic Active Radiation(PAR). The fitting range of Mass Water Content(MWC) is 15 0%～19 5%, Relative Water Content(RWC) is between 58 8% and 76 6%, the fitting PAR range is 600～1000μmol photons·m-2·s-1. In that range of MWC and PAR, Syringao blata lindl can get higher Pn and WUE, and will not waste water because of high T r, and the Pand WUE will weaken out of those range. The lowest MWC is about 11 6%(RWC is 45 7%), and the corresponding highest PAR is about 800μmol photons·m-2·s-1, the falling of MWC or the increasing of PAR will lead to serious aridity stress and high light stress. The results showed that in the hilly-gully region in semi-arid area, Syringa oblata Lindl. should be planted in the ubac rather than in the abret, or be planted under other trees to form mixed forest rather than pure forest, which may has higher productivity and effects.
2004, Vol. 2 
