Abstract:

The effects of three fire treatments of T1 (leaf burn),T2 (branch burn) and T3 (stem burn) on net photosynthetic rate,transpiration rate,water use efficiency and chlorophyll fluorescence parameters for young leaves of Fraxinus mandshurica,Juglans mandshurica and Quercus mongolica saplings were studied in this research. The results were shown as follows: 1) All net photosynthetic rates of young leaves of three tree species,except Q. mongolica whose net photosynthetic rate significantly decreased after T3 treatment,significantly increased after three fire treatments. 2) The water use efficiency of new leaves for Q. mongolica significantly decreased after T1 and T2 treatments,for F. mandshurica significantly increased after T1 treatment and there was no clear change for J. mandshurica after three treatments. 3) There was significant increase of new leaves' transpiration rate for Q. mongolica after T1 and T2 treatments,but no clear changes for F. mandshurica and J. mandshurica. 4) There were no regular change patterns of chlorophyll fluorescence parameters for new leaves of three tree species. The results indicated that the influences of fires on net photosynthetic rate and chlorophyll fluorescence parameters of young leaves related to the parts of burning and the fire-resistant capacity of saplings. The burning of some tree species will stimulate the tree's growth.

Key words: sapling, burning, gas exchange parameter, chlorophyll fluorescence parameters, photosystemⅡactivity