中文摘要：

以水曲柳、核桃楸和蒙古栎3种幼树为研究对象，研究3种火烧处理对幼树新生叶的净光合速率、蒸腾速率、水分利用效率和荧光参数的影响。结果如下：1）对水曲柳、核桃楸和蒙古栎进行3种火烧处理T1、T2、1、3（分别为：叶片被火烧、枝被火烧、茎被火烧）后，除了蒙古栎的1、3处理新生叶净光合速率显著降低外，其他处理新生叶的净光合速率都显著提高。2）蒙古栎的T1、T2处理新生叶的水分利用效率显著降低，水曲柳的T1处理新生叶水分利用效率显著提高，核桃楸的3种处理新生叶的水分利用效率无明显变化。3）蒙古栎的T1、T2处理新生叶的蒸腾速率显著提高，水曲柳和核桃楸的3种处理新生叶的蒸腾速率无明显变化。4）火烧后3种幼树新生叶的荧光参数的变化没有一定规律。研究表明火烧处理对幼树新生叶的净光合速率和叶绿素荧光参数产生不同的影响，这与幼树被火烧的部位和幼树本身抗火特性等因素有关。对一些树种进行适当的火烧会促进树木的生长。

英文摘要：

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.