Transpiration And Photosynthesis Characteristics Of Typical Plant And Its Influence On Element Migration In Karst Areas Of Southwest China

The transpiration characteristics of typical plant Vitex negundo at different geomorphological positions (Depression, Slope, Saddle), and the transpiration, photosynthesis and water use efficiency (WUE) characteristics under different geological background(limestone, dolomite, sandstone),were studied and compared. The dominant factors that influenced the transpiration rate and WUE were analyzed. On the other hand, the migration characteristics of primary elements at different geomorphological positions and that under different geological background were investigated. The correlation between migration of these elements and plant transpiration were studied, exemplified by typical plant Vitex negundo grown in the studying area.Some results were obtained as follows. (1) There were differences in diurnal variation of transpiration rate of Vitex negundo among different geomorphological positions and different geological background. The average diurnal transpiration rates in different geomorphological positions were in sequence as Saddle> Depression> Slope. The Vitex negundo in sandstone area had higher transpiration rate but lower photosynthesis rate and WUE than that in limestone area. (2)The dominant factors influencing transpiration rate of Vitex negundo were stomatal conductance, air relatively humidity and leaf temperature. The influence of stomatal conductance was the greatest, and the influencing extent varied with the geomorphological positions. The factors influencing the WUE of Vitex negundo included temperature, humidity, stomatal conductance and CO2 concentration, but the influencing extent varied obviously with the geological background. (3) The influence degree of plant transpiration on the migration and accumulation of the major elements, such as Ca,Mg,Cu,Fe,Mn and Zn, varied with different geological background and different elements. The plant transpiration had a certain promoting effect on migration of the elements, such as Mn and Cu, which were more difficult to transfer. Moreover, the influence degree of migration and accumulation of the microelements, such as Cu,Fe,Mn and Zn, on plant absorption coefficient, varied significantly with different geological background. In karst mountain areas, the characteristics of different geomorphological positions or different geological background should be considered when carrying out vegetation restoration, and suitable plant species should be chosen according to local conditions. These results could provide scientific basis for the choosing and cultivating of plants and management of karst rocky desertification in karst mountain areas.