This paper explores the responses of photosynthesis and fluorescence of Picea pungens Englenan on soil drought stress in Inner Mongolia region and clarifies the quantitative relationship between them and soil moisture.In this study,3-year old Colorado blue cedar potted seedlings were used as experimental materials,and the relative water content of soil(RWC) was controlled at 13.3%-83.3%.The combination of artificial water supply and natural water consumption was adopted to simulate the soil drought process under natural conditions,and the response process and mechanism of photosynthesis and fluorescence parameters of the leaves were analyzed.The results showed that the surface temperature gradually increased with the increase of the relative water content of the soil under increasing drought stress,and the surface temperature showed a sharp increase trend after RWC5.Surface humidity shows an opposite trend.As the soil relative water content(RWC) gradually reduce,the leaf gas exchange parameters are the changes of the lower of the first increase trend,among them,the leaf net photosynthetic rate(Pn),transpiration rate(Tr),water use efficiency(WUE),stomatal conductance(Gs) are maximum when relative soil water content for RWC5,illustrates the leaf gas exchange parameters there is a close relationship with the soil relative water content.Superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) first increased and then decreased with the relative water content(RWC) of the soil,which reached the maximum at RWC5,and then decreased sharply when the relative water content of the soil exceeded RWC5.Malondialdehyde(MDA) decreased with RWC.Regression analysis showed that Pn and WUE of leaves and RWC of Colorado blue cedar presented unitary quadratic equation(P<0.01).In addition,the chlorophyll fluorescence parameters of the leaves of the Colorado blue cedar show a trend of increasing and then decreasing with the relative water content of the soil(RWC),reaching the maximum at RWC5.When the relative water content of the soil exceeds RWC5,the chlorophyll fluorescence parameters drop sharply.Which shows that the Colorado this leaf gas exchange and chlorophyll fluorescence parameters on soil moisture have obvious response threshold,the threshold point of soil relative water content is about RWC5,below the threshold of leaf photosynthetic rate from stomatal limitation to the stomatal limitation,damage to the photosynthetic parameters,the electron transfer,photosynthetic mechanism is damaged.
