Endodormancy is a key determinant of cold and freezing hardiness in plant cycles. Short plant growth periods and increasing frequencies of frosting caused by increasing temperatures are major environmental challenges faced by trees in arid areas of central Mongolia. In the present study, the primary aim was to determine an effective method for cold hardiness with the use of six introduced and two Mongolian poplar clones. The secondary aim was selecting clones suitable for afforestation in Mongolia. Year old branches were subjected to four temperature treatments to induce cold hardiness. Electrolyte leakage, 2,3,5-triphenyltetrazolium chloride (TTC) reduction, leaf sprouting, and leaf browning rates were compared. High rates of electrolyte leakage and browning rates were observed along with low leaf sprouting at a low-temperature of ‒30°C. Temperatures between ‒25°C and ‒30°C damaged certain clones more than others. TTC reduction rate method for determining cold hardiness was considered effective in this case. In addition, Mongolian poplar P. sibirica differed distinctly from other poplar clones owing to the difference in dormancy-breaking whereas DN 247 and DN sim were better adapted to cold hardiness based on TTC reduction rate. These findings suggest that factors such as plant dormancy depth and physiological differences might significantly affect productivity and performance among plants. Evidently, further studies are required using other plant parts for selecting suitable poplar clones.

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The purpose of this study was to investigate responses of pear cultivars ‘Niitaka’ and ‘Chuwhangbae’ under short period heating on cold resistance level of flower buds. Experiment was conducted using annual shoots flower bud which were artificially heated (AH) during 72 hour at room condition (18–20°C). To assay for cold resistance, the cultivars were treated and observed under negative temperatures −10, −15, −20 and −25°C during the winter period in 2012 and 2013. Our findings revealed that ‘Chuwhangbae’ which was treated under control and artificial heating treatments was more resistant to low temperature than ‘Niitaka’ showing decreasing level of flower buds damages by mid-January although in early March an increasing level of damages was observed again. Cold resistant cultivar ‘Chuwhangbae’ responded more sensitively to external environments. This means that ‘Chuwhangbae’ restructures the plant protoplasts and process the transition to the new metabolic energy level in an efficient manner when triggered by effective negative temperatures thereby resulting in hardening process. We assume that this might be closely related with dormancy period, concentration of the mineral elements, water potential and transition processes of metabolism to the new energetic level. With a rise in temperature, cold tolerance in pear cultivars significantly decreased and this is related to intensive development of the floral organs. The chilling requirements for blossoming of ‘Niitaka’ was higher than ‘Chuwhangbae’.