重庆石灰岩地区木豆与十大功劳叶片气体交换的比较

对重庆石灰岩地区固氮植物木豆与非固氮植物十大功劳叶片气体交换进行了比较研究.结果表明木豆的日均净光合速率（Pn）、蒸腾速率（E）、气孔导度（Gs）和光能利用效率（LUE）均大于十大功劳,但两者的水分利用效率（WUE）没有差别.净光合速率在中午出现了较明显的光合＂午休＂现象.经分析木豆的光合午休主要由气孔因素引起,而十大功劳的光合午休现象以非气孔因素为主.同样,在季节变化中木豆的净光合速率（Pn）、蒸腾速率（E）、气孔导度（Gs）和光能利用效率（LUE）的季节均值也均大于十大功劳,但水分利用效率（WUE）却相反.木豆和十大功劳的叶绿素含量的季节变化与净光合速率季节变化趋势基本一致,木豆的叶绿素含量呈8月份高峰的单峰曲线,而十大功劳在8月份和10月份各有一高峰.木豆的叶绿素a/b的季节变化呈递减趋势,相反,十大功劳呈上升趋势.经分析,木豆和十大功劳的净光合速率的季节变化与叶绿素含量的季节变化相关联.木豆单位叶重的含氮量季节均值为37.6mg/g,明显高于十大功劳的14.8 mg/g,说明木豆的高固氮能力导致了木豆的高光合能力.但木豆的水分利用效率不如十大功劳,说明有高光合能力的固氮植物木豆在石灰岩地区的植被恢复中也存在其不适应的因素,但木豆是否真正适应干旱环境还需要进行全面的水分生理的研究.

Leaf gas exchange characteristics of Cajanus cajan and Mahonia fortunei in the limestone area in Chongqing, China

Drought stress is often a feature of limestone areas,making it difficult for plants to grow well.Therefore it is important to find drought-adapted species for vegetation restoration in limestone areas.Cajanus cajan is a nitrogen-fixing shrub that was introduced to some limestone areas such as Guangxi and Guizhou provinces of China.Mahonia fortunei,a non-nitrogen-fixing shrub,is a predominant species in the Chongqing region.The diurnal and seasonal variations of gas exchange and leaf N content of the two species were compared in order to understand their adaptive ability with respect to the limestone habitat.Net photosynthetic rate(Pn),transpiration(E),stomatal conductance(Gs) and light use efficiency(LUE) in leaves of C.cajan were higher than in leaves of M.fortunei,while both species showed midday photosynthetic depression.The results for stomatal conductance(Gs) and intercellular concentration(Ci) indicated that the photosynthetic depression was caused by stomatal limitation in C.cajan while the depression of Pn in M.fortunei was predominantly due to non-stomatal limitation.However,water use efficiency(WUE) in leaves of C.cajan was lower than in leaves of M.fortunei.The seasonal variations of chlorophyll a,chlorophyll b and chlorophyll(a+b) content of both species showed the same trends as the seasonal variations of Pn.The contents of chlorophyll a,chlorophyll b and chlorophyll(a+b) in leaves of C.cajan had a peak in August and then declined while for M.fortunei,besides a peak in August,there was another peak in October.The chlorophyll a/b ratio in leaves of C.cajan declined with the months passing,whilst that in leaves of M.fortunei increased.The net photosynthetic rates of both species were positively correlated with their chlorophyll contents.The leaf N content of C.cajan was 37.6 mg/g,much higher than that of M.fortunei(14.8 mg/g),implying that the nitrogen-fixing capacity of the former causes its high photosynthetic capacity.However,because of its lower WUE,C.cajan has a disadvantage in drought conditions in limestone areas.Water-related physiological characteristics should be studied further in order to understand completely whether it can be adapted well to such conditions.