db2表空间缩减问题？

db2的表空间执行：
 db2 "alter tablespace USERSPACE1 Reduce (file '/opt/sisc/test/testdb/db2inst1/NODE0000/TESTDB/T0000002/C0000000.LRG' 32M)"
报错：
DB21034E  The command was processed as an SQL statement because it was not a 
valid Command Line Processor command.  During SQL processing it returned:
SQL20318N  Table space "USERSPACE1" of type "AUTOMATIC STORAGE" cannot be 
altered using the "ADD" operation.  SQLSTATE=42858