中文摘要：

利用Li-6400便携式光合作用测定系统,研究自然条件下不同年龄人工林尾巨桉（2年生、4年生和6年生）叶片光合特性及水分利用效率.结果表明：一年中桉树人工林叶片净光合速率、蒸腾速率和水分利用效率的月动态呈现单峰曲线,以8月份为最高,1月份为最低;从9月到第2年1月逐渐减低,从2月到8月缓慢增加;胞间CO2浓度的月动态与其相反.不同林龄桉树人工林叶片净光合速率、蒸腾速率和水分利用效率从2013年9月到2014年4月大小顺序为4年〉2年〉6年,而从2014年5月到8月大小顺序为2年〉4年〉6年;净光合速率、蒸腾速率和水分利用效率的年平均值大小顺序为2年〉4年〉6年,2年、4年、6年的年水分利用效率平均值为2.33μmol/mmol、2.28μmol/mmol、2.17μmol/mmol,且净光合速率与胸径增长量呈显著正相关（P〈0.05）.桉树人工林叶片净光合速率、蒸腾速率和水分利用效率与气孔导度、大气温度、光合有效辐射呈极显著（P〈0.01）或显著（P〈0.05）正相关,与胞间CO2浓度呈负相关.随着林龄的增加,净光合速率、蒸腾速率和水分利用效率逐渐降低,因此桉树人工林早期对水分及养分需求大,进行合理地养分管理和定向培育,可实现桉树的可持续经营.

英文摘要：

Photosynthesis and water use efficiency affect the growth of trees.Studying the changes of photo synthetic characteristics and the water use efficiency of Eucalyptus urophylla × E.grandis plantation is important for maintaining the soil nutrient balance and realizing the sustainable management of eucalyptus.We conducted a field experiment from September2013 to August 2014 at the Tianma National Forestry Farm（117°24＇29 ＂E,24°18＇29＂ N） of Zhangzhou,Fujian Province,China.The Li-6400 portable photosynthesis system was used to study the characteristics of photosynthesis and water use efficiency under the natural condition.The experiment objectives included E.urophylla × E.grandis plantations of 2 years old（2 yr）,4 years old（4 yr）,and 6 years old（6 yr）.The results showed a ＂single peak＂ curve for the monthly dynamics of the net photosynthesis rate（Pn）,transpiration rate（Tr） and water use efficiency（WUE）,with the highest value in August and lowest in January.All the Pn,Tr and WUE values reduced gradually from September 2013 to January 2014,then increased gradually from February to August 2014,while the intercellular CO2 concentration（Ci） showed an opposite trend.The Pn,Tr and WUE values from September 2013 to April 2014 were in the order of 4 yr〉 2 yr 〉6 yr,but in the order of 2 yr 4〉yr 6 〉yr from May to August 2014;the annual averages Pn,Tr and WUE were in the order of 2 yr 〉4yr 〉6 yr,where Pn had a significantly positive correlation with the DBH increment.The annual WUE average was 2.33 μmol mmol^-1 for 2 yr plantations,2.28μmol mmol^-1for 4 yr,and 2.17 μmol mmol~（-1） for 6 yr eucalyptus plantations.The Pn,Tr and WUE of eucalyptus plantations were significantly and positively correlated with the gas stomata conductance（Gs）,air temperature（Ta） and photo synthetic active radiation（PAR）,but negatively correlated with Ci.With the increase of the plantation age,the annual average value of Pn,Tr and WUE decreased gradually.Therefore,eucalyptus pl