Freezing nights and shorter days depress levels of chlorophyll in leaves.寒冷的夜晚和缩短的白天降低了叶子中的叶绿素含量。The green colour of the leaf is due to a substance called chlorophyll.叶子之所以是绿色的是因为一种称为叶绿素的物质在起作用。Chlorophyll is a group of green pigments.叶绿素是一组绿色色素。Chlorophyll is essential to plant prosperity.叶绿素对植物的茁壮成长是必不可少的。