Abstract:

In this paper, physiological index of Black Locust (Robinia pseudoacacia), Oriental Arborvitae (Platycladus orientalis) and Apple (Malus pumila) under different soil water condition in the catchment afforestation field and under the condition of water menace was measured by portable photosynthesis system (LI-6200) and portable steady porometer (LI-1600) in Fangshan, Shanxi Province. The quantitative relation among net photosynthesis rate, carboxylation efficiency and water use efficiency with soil water content was studied. The result shows optimum soil water content keeping max net photosynthesis rate of Black Locust, Oriental Arborvitae and apple is 17.13%、15.9% and 16.11% in turn. Optimum soil water content keeping better leaf water use efficiency of three kinds of tree is 13.23%、10.17% and 12.38%. Soil water content is 15.7%, 15.5% and 15.8% in turn with the highest carboxylation efficiency respectively. Soil water compensation point for hydration of three kinds of tree is 4.55%, 3.91% and 4.49%. The suitable soil water content for transpiration rate of three kinds of tree is 18.82%, 19.70% and 16.33% respectively. According to the thought of catchment afforestation, the soil water content maintaining the best leaf water use efficiency can be chosen as a critical value for tree density control in catchment afforestation and the lowness value for calculating tree water requirement. This general index can be shown as 10%～13% for Black Locust, 10%～12.5% for Apple and 9.5%～11% for Oriental Arborvitae.

Key words: Catchment afforestation, Suitable soil water content, Photosynthesis rate, Transpiration rate, Water use efficiency