Ecophysiological Studies on Water Storage and Water Stress in Tree Species

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Rate of photosynthesis and transpiration of Q.serrate and Cinnamomum Camphora could not show any response to the changes in environmental conditions under severe drought stress cause by the sudden cessation of irrigation. On the other hand, long by weak drought stress was conquered by the phenological and physiological response of seedlings of several tree species. Especially the greater the degree of water stress was, the faster the physiological response of leaves occurred. Four big tree species (Cryptomeria japonica, Chamaecyparis obtusa, Magnolia salicifolia and Quercus serrata) were cut before the dawn and whole top part were hung by load-cell to measure the changes in total weight. At the same time, water supplied from the cross section of the trunk. Heat pulse method was used to monitor the changes in sap flow velocity (HPV : heat pulse velocity) by the cut of stem. Just after the cut of stem, C.japonica, C.obtusa and M.salicifolia showed a sudden and tentative increase in HPV (HPVpul), because the negative pressure in xylem was dissolved by stem cutting and water supply. Q.serrata, however, did not show such a sudden increase in HPV.The HPVpul of C.japonica and C.obtusa returned to the normal level after 1.5 and 2.5 hours, respectively. On the other hand, that of M.salicifolia disappeared after only one hour from the top severance, indicating that M.salicifolia could supply water easier than C.japonica and C.obtusa. It means that a tracheid system in coniferous species has higher resistance to water flow in a tree trunk than a vessel system in ring porous xylem. The ratio of HPVpul to the daily maximum HPV of C.japonica increased with the depth from the trunk and it exceeded unity at 18 mm depth, which means HPVmax before the top severance did not represent the maximum capacity of water conductance.