Study on Diurnal Variation of Water Use Efficiency of Cercis chinensis Leaves in Summer

The diurnal variations of net photosynthetic rate(P n),Transpiration rate(T r),stomatal conductance(G s)and water use efficiency(WUE)of Cercis chinensis leaves under natural conditions had been studied.The results were as follows:In summer clear days,the curves of diurnal variations of P n had two peaks,which had an obvious phenomenon of midday decline of photosynthetic efficiency.The mid-depress of P n was principally caused by non-stomatal limited elements.T r and G s had single peak which showed the maxmum at noon.WUE were higher at sooner or later ,and were lower at noon,the correlations,P n,T r,G s and WUE to some environmental factors were all singificant at 0.01 probability level.The most excellent equation of the diurnal variation of P n,T r,G s and WUE were attained by the methods of stepwise multi-regression respectively.