问题 问答题 简答题

苗木越冬死亡的主要原因有哪些?

答案

参考答案:

苗木冬季在原地越冬常会出现死亡现象,主要有以下原因:

生理干旱在早春因干旱风的吹袭,而地下部又因土壤冻结,根系难于吸收水分,使苗木地上部分失水太多而致死。

地裂伤根因冬季严寒,地冻开裂拉断苗木根系,或被风吹干而致死。

冻死因严寒使苗木细胞原生质脱水冻结,损伤了细胞组织,失去了生理机能而致死。

光氧化伤害北方苗圃培育的常绿性针叶树苗木,如果不覆盖防寒,则苗木针叶变黄,严重时影响第二年生长,甚至死亡。

完形填空
完形填空。
     "Who did this?" asked my teacher. Thirty children tries to think  1  not only what they had done, but also
what our teacher might have found out.
     "Who did this?" she asked again. She never became angry, but she was this time. She held up  2  broken
glass and asked,"Who broke the window?"
     "Oh, oh" I thought. I was the one  3  broke the window. I did not do it on purpose. It was caused by a
  4  throw of a baseball. Why did it have to be me?
     If I admitted it, I would  5  in a lot of trouble. How would I be able to pay for a big window like that? I
didn't want to raise my hand,  6  something much stronger than me pulled me up."I did it. Then I was silent. 
 7  was hard enough saying what I had.
     My teacher went to the bookshelf and took down a book. She then began walking to my desk. I feared she
was going to punish me.
     "I know how you like birds," she said  8  she stood looking down at my face. "Here is a book about birds.
It is your now. You will not be punished. But remember, it's only  9  your truthfulness."
     I couldn't believe it! I wasn't punished and I was getting a book! The  10  one that I had been saving up
all my money to buy.
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