The effect of low-temperature event on the survival and growth of Juglans mandshurica seedlings within forest gaps

In forest ecosystems, gap formation changes the allocation of abiotic resources and thus affects the survival and growth of understory plants. However, how tree seedling survival and growth respond to low-temperature events and the influencing mechanisms remain unclear. To clarify how low-temperature event limits the survival and growth of tree seedlings in the montane regions of eastern Liaoning Province, northeast China, we investigated temperature and light intensity within secondary forest gaps, and the survival and growth of Juglans mandshurica seedlings after a low-temperature event in the spring of 2014. Damage to seedlings due to low temperature sig- nificantly varied in different aspects. Seedlings in gaps on southeast-facing slopes were the most seriously damaged, followed by those in gaps on northeast-facing slopes. In contrast, seedlings in west-facing gaps and in control plots without slope aspect were not damaged. The freezing injury index for seedlings was negatively correlated with minimum temperature （r = - 0.608, P 〈 0.01）, but it was positively correlated with light intensity （r= 0.818, P 〈 0.01）. In addition, height and root collar diameter of damaged seedlings were significantly lower than those of the undamaged seedlings （P 〈 0.01） during the early growing season （April-July）, but no significant difference were observed during the late growing season （July-Oc- tober） （P 〉 0.05）. The extent of seedling damage was directly related to slope aspect. Low temperature and high light intensity were found to be the dominant factors affecting extent of damage to seedlings on southeast- and northeast-facing slopes.

Evaluation on Climate Suitability in Main Growth Stages of Zhaotong Apple in Recent 60 Years

Based on daily average temperature,precipitation and sunshine hours during 1961-2018 from two meteorological stations of Zhaoyang District and Ludian County at Zhaolubazi,Zhaotong City,Yunnan Province,using the freezing injury index at flowering stage(Ha),climatic suitability index during expansion period(Pa),climatic suitability index during coloring period(Dy)and climatic suitability index during fruit growing period(Si),etc.,the climatic suitability of Zhaotong apple during the main growth stages was evaluated.The results showed that the annual average temperature was 11.8-12.3℃at Zhaolu Bazi in recent 60 years,and the climate was the most suitable for Fuji apple planting both in the south and north;the average annual precipitation was 674.8-852.6 mm,and the climate was suitable in the north and sub-suitable in the south;the annual average sunshine hours was between 1845.4 and 1851.1 h,and the climate was sub-suitable in both areas.The Ha was between 0.42-0.50,serious in the north and moderate in the south;the Pa was between 0.92 and 1.02,and both the south and the north were suitable areas;the Dy was between 0.95 and 1.00,and the climate in the south was suitable,while it was sub-suitable in the north;the Si was between 1.38 and 1.59,and the climate was suitable in the south and sub-suitable in the north.There was a 4-year cycle in the interannual variation of Ha,Pa,Dy and Si.After the 1980s,the Ha decreased by 0.56-0.59,the Pa,Dy and Si respectively increased by 0.10-0.16,0.14-0.15 and 0.78-0.84 with the temperature rise,and the changes of these four indexes were all favorable for Fuji apple's fruits growth.It can be seen that under the background of the global warming,the climatic conditions in Zhaolu Bazi are becoming more and more favorable for popularizing the planting of Fuji apple.