Drought resistance of Prunus mume, Prunus jamasakura and Quercus serrata at decreasing process of soil water content
Water stress is one of the main factors to induce tree decline, and affects tree growth in combined with other stresses (air pollution etc.). Only processes of forest decline participated with water stress have been investigated, the mechanism of decline have not been clarified. In this study, drought resistance in Prunus mume, Prunus jamasakura and Quercus serrata were estimated under soil water declining process by using the response of transpiration rate, stmatal conductance and visible injury occurrence. Potted trees were irrigated sufficiently until the soil water dripped from under the pots. Two hours later, the soil surfaces and the gapes of pots were closed up with styrene foam board. The pots weight were measured continuously by load-cell in glasshouse. The transpiration rate and the soil water content were calculated by measuring of the pot weights. During this experiment, the gravimetric water contents of soil were reduced from 75 % to 20 %.(1) Variable factors of transpiration The transpiration rates reduced with the regression coefficient (k) decreasing with soil water contents as hereunder. Transpiration rate (E) = regression coefficient (k)×solar radiation (Sn) The relationship between soil water contents and regression coefficients (k) were able to be expressed by sigmoidal function in the all tree species.(2) Visible injury Wilting, reduction of chlorophyll, and defoliation were observed in Prunus mume with decreasing of soil water contents. Prunus jamasakura showed death of whole plant as well as wilting in the process of treatment. On the other hand, visible injury was not observed in Quercus serrata.(3) Regulative capacity of transpiration Quercus serrata had the highest regulative capacity of transpiration by regulation of stomatal aperture, because the rising of stomatal resistance caused at highest soil water content in three species. Regulative capacity of transpiration was lowest in Prunus mume, but the amounts of transpiration in whole trees were decreased by the defoliation. Based on these results, Prunus mume is easy to develop visible drought injury, but could be able to survive under the strong drought condition due to defoliation. On the other hand, Prunus jamasakura is sensitive to drought, since the resistance to tissue drying is low and the effective adaptation for drought does not develop. Quercus serrata is the highest drought resistant species, because of having high regulative capacity of transpiration and strong tolerance to tissue drying.
|deciduous broad leaved tree
|gravimetric soil water content