| Pinus sylvestris L. var. mongolica Litv. is one kind of silvicultural and ornamentaltrees in Northern China. They can adapt themselves to very low temperature. We carriedout an experiment for11-year-old seedlings in Pinus Sylvestris L. var. mongolica Litv.There were three treatments involved in the trial: delayed soil-thawing treatment (FROST)(In this treatment, anything on earth was shoveled during winter2011, thus facilitating soilfreezing. At the beginning of March2012the ground was covered with insulation, whichconsists of plastic layers, dry needles and grass. The insulation was retained until thebeginning of July2012); Open treatment (OPEN)(In this treatment, the earth was keptclear until the beginning of July2012); Control treatment (CTRL)(This treatment was keptnatural). The aims were to study the effect of delayed soil-thawing on the growth and frosthardiness of Pinus Sylvestris L. var. mongolica Litv. during the dehardening. The frosthardiness (FH) of needles and stems was measured by the method of electrical impedancespectroscopy (EIS). The growth of new stems’ length and roughness, new needles’ lengthand the status of budburst were recorded, and the soluble sugar and starch concentration,malonal dehyde level (MDA) and water content in needles and stems, the chlorophyllconcentration and the maximum photochemical efficiency of photosystem II (Fv/Fm) weremeasured, respectively. The FH, parameters of EIS and enzymes related were measured atthe different phases of Pinus sylvestris L. var. mongolica Litv. The additional aim was toverify the correlation among the parameters of EIS, growth and physiological indicators,and to find the change trend in these parameters. Research on responses of growth andfrost hardiness to delayed soil-thawing in needles and stems of Pinus sylvestris var.mongolica during dehardening by the method of EIS is helpful to make large-scaleafforestation scheme under the soil-thawing condition.The following are the main results:1. The spectroscopy shape of stem changed from single-arc to double-arc as FHdecreased during dehardening. And the appearance of double-arc in FROST wasearlier than CTRL. The spectroscopy of needles was kept single-arc all the time.2. The spectroscopy of needles and stems in three treatments became smaller asdehardening process and reached the smallest at the end of June. The bigdifference of spectroscopy between FROST and CTRL is in April (P<0.01). 3. As dehardening process, the FH of Pinus sylvestris L. var. mongolica Litv. of threetreatments gradually decreased. The FH of stems and needles in OPEN wasdecreased faster than others at the beginning of dehardening. The biggestdifference in FH between FROST and CTRL happened in April2012.4. During dehardening, the parameters of EIS (the specific resistance r and r1,extracellular resistance re, intracellular resistance ri, and relaxation time τ1) instems were kept decreased. The values of these parameters in FROST were highersignificantly than those in CTRL (P<0.05). Their changes in needles were different,and the change was slow in early time and decreased gradually late.5. The growth peak of new stems and needles in FROST was later than in CTRL andthe biomass of stems and needles were significantly lower in FROST than in theother treatments (P<0.001).6. Relation was found between the growth of new needles and stems and theaccumulated temperature (>0℃) at depth of20cm. The relation in FROST was notmore significant than the other. And this relation in needles was more obvious thanin stems.7. The soluble sugar and starch concentration were more in CTRL than in FROSTand OPEN at the month of April and May (P<0.01). And there was no significantdifference in needles among three treatments.8. The chlorophyll concentration was significantly lower in FROST and OPEN thanin CTRL in June (P<0.01). |
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