That's actually part of a process known as abscission, where most deciduous trees shed their leaves after their colors change from a loss of chlorophyll, the chemical that's involved in photosynthesis.
这实际上是称为脱落的过程的一部分,大多数落叶树在颜色因叶绿素损失而改变后脱落,叶绿素是参与光合作用的化学物质。