Before the 49th day after silking, SS activity presented single peak curve and it came to the peak value in the 21st day, then fell slowly.

• 在吐丝49天之内，SS活性呈单峰曲线变化，到吐丝21天达到高峰，之后缓慢下降，但高氮处理下降速度慢于低氮处理；