Physiological Responses Of Thuja Sutchuenensis To Natural Temperature Reduction And Characters Of Seed And Cuttage Propagation

Thuja sutchuenensis Franch, first discovered in1892and had not been seen againfor almost100years thereafter, is an evergreen tree of Thuja, Cupressaceae. It isnaturally distributed in Daba mountain range in Chengkou and Kaixian country, China.It has been listed as a critically endangered species by the World Conservation Union(IUCN-SSC) in2003.Physiological responses of endangered species to low temperature are thetheoretical bases for ex-situ conservation. Propagation of population by seed andcuttage is a key step for saving endangered species. In this study, cultivated T.sutchuenensis saplings introduced into Beijing for3years were choose as experimentmaterials, physiological responses and adaptive mechanisms to natural temperaturereduction, seed characters, and cutting propagation are investigated to provide ascientific basis for its population propagation and effective conservation. Platycladusorientalis (L.) Franco of the same age and condition were chosen as control. The mainresults we obtained are as follows:1. With the temperature falling process in immigrant areas, some obvious damagesymptoms including rolled and withered leaves occurred, while the trunk and robustlateral branches have no such obvious damage symptoms. When temperature rised inspring, buds sprout again from the internodes. All saplings almost survived. Whereas,comparison group P. orientalis individuals from immigrant areas appeared no damagesymptoms.2. With the falling of temperature, net photosynthetic rate (Pn), maximumphotosynthetic rate, apparent quantum yield, transpiration rate, stomatal conductance,chlorophyll content, conversion efficiency of primary light energy of PSⅡ, potentialactivity of PS II, effective photoelectron yield of of PS II, coefficients of photochemical and non-photochemical quenching were decreased, However, theintercellular CO2concentration is higher and dark respiration rate increased. Whentemperature dropped to daily mean temperature (-6.40℃) and daily minimumtemperature (-10.46℃), the net photosynthetic rate of T. sutchuenensis saplings is zero.Photosynthetic parameters of P. orientalis saplings were similar to T. sutchuenensisexcept the intercellular CO2concentration. With the decrease of temperature, theintercellular CO2concentration of P. orientalis increased.3. With the falling of temperature, the superoxide dismutase activity of T.sutchuenensis saplings evidently increased, the peroxidase activity basicallyunchanged while the superoxide dismutase and the peroxidase activity enhanced at thesame time. The proline and soluble sugar content of both two species leaves increasedsignificantly, but the rate of T. sutchuenensis is lower than P. orientalis. Although theMDA content of both two species leaves also increased significantly, but the rate of T.sutchuenensis is higher than P. orientalis. Daily minimum temperature closely relatedwith the superoxide dismutase activity, the peroxidase activity and the soluble sugarcontent of P. orientalis. Howerer, daily minimum temperature only closely related withthe superoxide dismutase activity of T. sutchuenensis. It indicated that P. orientaliscould adjust itself well to adapt to low temperature environment compared with T.sutchuenensis during seasonal natural cooling process.4. The mature cone of T. sutchuenensis is ellipsoidal,8.34mm in length,4.54mmin width on average. Seed amount of a single cone is4.5on average. Seed is3.25mmin length,1.13mm in width,0.96mm in thickness,1.4962g of1000-seed-weight onaverage. The germination rate, germination index and seed vigour indexes of T.sutchuenensis seeds is24%,2.19and29.25%respectively. Seed traits of differentcollection period are different. The best developed cones of T. sutchuenensis collectedin late October. It suggested that the best collected period of T. sutchuenensis conesmay be in late October.5. With cuttage collected from2-year old arborvitae tree branches and cultivatedon medium of peat, vermiculite and pearlite (v:v:v=1:1:2) disposed in GGR1000mg·L-1two minutes, rooting rate was35%after130days. Analysis of variance showedthat younger trees of T. sutchuenensis have higher rates of rooting. That is to say, therooting rate of T. sutchuenensis is closely related to the mother tree age. The youngerof the T. sutchuenensis mother tree, the higher of the rooting rate.