Abstract: ObjectivePhysical response of Panax notoginseng(Burk.)F.H.Chen to low temperature stress and high temperature stress were studied,and its cold and heat resistance mechanism were revealed to provide theory basis for breeding of resistant varieties regionalized cultivation,cultivation and management of P. notoginseng.MethodPotted second-year P.notoginseng seedlings were used as tested materials,and treated by 5,10,25(control)and 35℃in artificial climate box.After 48 h of continuous treatment,physiological indexes including photosynthetic characteristics,chloro-phyll contents,protective enzyme activities were studied and the changing rules were analyzed.ResultUnder the tem-perature from 5 to 25℃,the variation of chlorophyll a(Chla)content,chlorophyll b(Chlb)content and total chlorophyll (a+b)content rose at beginning then declined.Compared with 25℃treatment,the contents of chla,chlb,chl(a+b)re-spectively decreased 21.91%,23.30% and 22.78% in 5℃treatment,but compared with 10℃treatment,the contents of chla,chlb and Chl(a+b)respectively increased 51.69%,52.43% and 51.96% with the differences at significant level(P<0.05,the same below).Under 35℃treatment,the contents of chla,chlb and chl(a+b),and chl(a/b)decreased 14.61%, 6.80%,11.74% and 8.10% respectively comparing with 25℃treatment and the difference reached significant level.Under low temperature stress,maximum net photosynthetic rate(Pmax),apparent quantum efficiency(a),light saturation point (LSP),net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)decreased significantly,CO2 concentration(Ci)increased significantly and the change trend of the light compensation point(LCP)rose at beginning then declined.Under high temperature stress,Pmax,LSP,Pn,Gsand Trdecreased significantly,and Ci,a and LCP presented an increasing tendency. Under low and high temperature stress conditions,the activity of catalase(CAT)in P.notoginseng significantly reduced,and the activities of peroxidase(POD)and superoxide dismutase(SOD)generally increased signifi-cantly. Malonaldehyde(MDA)changed slightly. Under low temperature stress,soluble protein content significantly in-creased.ConclusionThe photosynthetic capacity of P.notoginseng is significantly inhibited by low and high temperature stresses.Under low temperature stress,P.notoginseng enhances the cold tolerance mainly by improving the activities of POD and SOD,and increasing the contents of chlorophyll and soluble protein.Under high temperature,P.notoginseng en-hances the heat tolerance mainly by improving the activities of POD and SOD.