Effects Of Soil Frost On Frost Hardiness In Pinus Sylvestris L.Var.Mongolica Litv.

The11years old Pinus sylvestris L. var. mongolica Litv. was used to study the effectsof soil frost on frost hardiness (FH) during cold hardening through three snowcontrolling processes: natural snow and melt (control), winter snow removed, andwinter snow removed and insulated. The FH of needles and stems was measured bymeans of the electrical impedance spectroscopy (EIS) and electrolyte leakage (EL)methods, and the changes of contents of dry matter, soluble sugar, starch, solubleprotein and proline. etc were also measured to analyse the relesions between FH andabove parameters. The relationships between parameters of electrical impedance andphysiological and biochemical indicators, as well as FH were validated with thepurposes to ascertain the impacts of soil frost on electrical impedance parameters, andalse to seek more convenient method to estimate FH of Pinus sylvestris L. var.mongolica Litv., and improve the EIS method for plant FH estimation technology.The main results were as follows:1. During cold hardening, the FH of each treatment increased sharply. The FH ofstems and needles measured by EIS and EL presented similar tendency.2. With the enhancement of the FH, the electrical impedance spectra and EISparameters of stems and needles changed during cold hardening. Aftercontrolled freezing tests, the membrane time constant mof needles and therelaxation time of stems correlated with FH (R2=0.50-0.89and R2=0.66-0.77,respectively), indicating that these parameters could be used for FH assementof needles and stems.3. For non-frost-exposed needles, the extracellular resistance reand intracellularresistance rifor snow removed treatment differed significantly with the othertwo treatments at the end of cold hardening (Mar.), but had no defferences atthe other months. For non-frost-exposed stems, rehad significant differentcesbetween treatments in early phase of cold hardening (from Sep. to Oct.),however, it became similar at the end of cold hardening (from Nov. to Mar.).The riof stems between different treatments was similar during coldhardening except Sep. The mof non-frost-exposed needles betweentreatments was also similar at any months except Oct. The ofnon-frost-exposed stems between treatments had significant differencesduring the whole cold hardening.4. During cold hardening, the contents of dry matter, soluble sugar and starchchanged with the FH. In the early phase of cold hardening (Sep.), the contentsof soluble sugar and starch in needles differed significantly between differenttreatments. No differences were found for the contents of soluble sugar andstarch in stems, as wellas the content of chlorophyll in needles in the samephase under different processes.5. During cold hardening, the content of proline in both needles and stems had the opposite trend with the FH, but no correlation was observed. FromSeptember to November, the proline content of needles has no differentbetween treatments, whereas the proline content of stems differs significantlybetween different treatments in different phases of cold hardening.6. During cold hardening, the superoxide dismutase (SOD) activity of needlesreduced firstly and then maintained the same trend, and the peroxidase (POD)activity of needles increased gradually. The SOD and POD activities ofneedles had no differences in the same phases of cold hardening. The SODactivity of stems in the control was rising gradually, while the other twotreatments showed a trend of increase first and then decrease. The PODactivity in stems of three treatments increased gradually, and the differencesof POD activity in stems had no differences in the same phases underdifferent treatments.7. During cold hardening, the contents of water, soluble sugar and starch inneedles and stems related with FH, suggesting that these parameters could beused to estimate FH of Pinus sylvestris L. var. mongolica Litv.