The changes of photochemical quenching(q P) and non-photochemical quenching(q N)of chlorophyll a fluorescence in leaves of four tree seedlings (Gleditsia sinensis,Juglans regia, Diospyros kaki and Diospyros lotus) were different between two different water stress ways:detached drought treatment and potted drought treatment. After 4 hours dehydration by leaf detaching,the q P values had significant decrease except J. regia, only 6 hours later, the q P values compared with contrast decreased significantly in four tree seedlings(P>0.05), but the range of reduction(G. sinensis, J. regia and D. lotus) was just 2.5% to 6.4%. D. kaki,however,got to 31.3%. While the q N values increased significantly with conducting dehydration of the detached leaves. However, the q P values of four species showed no significant decrease when they were growing in pots under soil water stress(40%～60%RWC) for 30 days; and the q N values decreased obviously with a exception in J. regia, which was consistent with that of detached leaf treatment. The results suggested that some difference or changes in mechanism of excess light energy dissipation might perform in four seedlings by short-term and long-term water stress.
