Effects Of Temperature And Photoperiod On Frost Hardiness In Seedlings Of Pinus Sylvestris L. Var. Mongolica Litv.

Mongolia Scotch pine (Pinus Sylvestris L. var. mongolica Litv.) is a kind ofsilvicultural tree and ornamental tree in North-China. It is able to adapt to very lowtemperature. We carried out a growth chamber experiment for 2-year-old seedlings inPinus Sylvestris L. var. mongolica Litv. There were four treatments involved in the trial:a long photoperiod (16h light: 8h dark cycle) with a high temperature (15℃) (LDHT), along photoperiod (16h light: 8h dark cycle) with a low temperature (3℃), a shortphotoperiod (8h light: 16h dark cycle) with a high temperature (15℃), and a shortphotoperiod (8h light: 16h dark cycle) with a low temperature (3℃). The aims were tostudy the effect of temperature and photoperiod on the development of frost hardinessand to test whether the effect of both factors was additive. Frost hardiness of needles,was measured by the methods of electrolyte leakage (EL), visual scoring of damage(VSD) and chlorophyll fluorescence (CF) respectively, frost hardiness of buds and stemswere measured by EL. The dry weight/fresh weight ratio (DW/FW), soluble sugar andstarch concentration of stems and needles, the chlorophyll concentration as well as themaximum photochemical efficiency of photosystemⅡ(F_v/F_m) of needles were measured.The frost hardiness, parameters of electrical impedance and enzymes related weremeasured for the different year old and different phase trees of Pinus Sylvestris L. var.mongolica Litv. growing in the field. The additional aim was to verify the correlationbetween the parameters of electrical impedance as well as enzymes and the frosthardiness, and to find the change trend with varied phases in these parameters.The main results are as follows:1. A stationary level of frost hardiness was reached in buds, stems and needles inPinus Sylvestris L. var. mongolica Litv. in a given temperature and photoperiod treatment.Stationary level of frost hardiness reached in needles, stems and buds varied.2. The effects of low temperature and short photoperiod on frost hardiness in PinusSylvestris L. var. mongolica Litv. were not additive.3. High temperature and long photoperiod could increase in frost hardiness, and itwas not supportive to the assumption that high temperature and long photoperiodtreatment should keep the minimum level of frost hardiness without changes for eachorgan. 4. The results of frost hardiness of needles differed in these three methods, however,they had correlations. Frost hardiness should be evaluated by integrated approach as onemethod as main practice but complemented with other methods.5. Correlations between dry matter content and frost hardiness in low temperaturetreatment were high, but low in high temperature; the relation between chlorophyllconcentration and frost hardiness was not regular; polynomial correlation was foundbetween the F_v/F_m of the non-frost-exposed needles and the frost hardiness of the needles;there was no direct correlation of soluble sugar as well as starch concentration of stemsand needles with frost hardiness.6. Age of tree had stronger effect on impedance spectroscopy and their parametersthan stage of annual growth period did.7. Impedance parameters relaxation time (τ_l) of freezing exposed stems and cellmembrane time constant (τ_m) of freezing exposed needles could be used as extracellularresistance (r_e) for frost hardiness assement.8. The stronger the frost hardiness of Pinus Sylvestris L. var. mongolica Litv. was,the higher the superoxide dismutase (SOD) activity was, and the lower peroxidase (POD)activity was. Vice versa.9. The stronger the frost hardiness in Pinus Sylvestris L. var. mongolica Litv. was,the higher the soluble protein content was. Vice versa.10. The stronger the frost hardiness of Pinus Sylvestris L. var. mongolica Litv. was,the lower the Malonal dehyde level content was. Vice versa.