The physiological characteristics of Robinia pseudoacacia and Pinus tabulaeformis seedlings under different soil water contents

Under fitted soil water content (70% θ_(f)), medium drought (55% θ_(f))and serious drought (40% θ_(f)),the growth and water use characteristics of Robinia pseudoacacia L. and Pinus tabulaeformis Carr. were studied. The results showed that survival rate, photosynthesis rate and biomass accumulation of two tree seedlings decreased significantly with the soil water content decrease. The water use efficiency of R. pseudoacacia leaves was the highest in fitted soil water content, it was the lowest under serious drought. Season of fast branch growth of two tree seedlings was mainly in March-June. Two tree seedlings all grew well under favorable soil water content and medium drought, their growth were all significantly inhibited under serious drought. The total water consumption, biomass and water use efficiency of R. pseudoacacia were significantly higher than that of P. tabulacformis under the three soil water contents. The total water use efficiency of the two tree seedlings was the highest at medium drought, that was the lowest under serious drought. The water consumption of R. pseudoacacia was higher than that of P. tabulaeformis. The ability of drought resistance of P. tabulaeformis was higher than that of R. pseudoacacia. R. pseudoacacia did not have the character of drought resistance plants, so it was not fit to plant widely in loess plateau area and only fit to favorable soil water condition. P. tabulaeformis should be planted in areas of high soil water content , such as shady slopes, gaps,channels, etc.