Drought resistance mechanism of tree species growing in Loess Plateau of China estimated by δ13C analysis

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Drought resistance mechanism of tree species growing in Loess Plateau in China was investigated. Annual rings of Pinus tabulaeformis and Robinia pseudoacacia, which are the most popular species for forest plantation in that region, were splitted to early- and latewood of each year. Holocellulose of the wood samples were analysed for isotope ratio of ^<13>C. From the measurements, δ^<13>C of early- and latewood were shown to have correlation to air temperature and precipitation in certain periods. In Pinus tabulaeformis, δ^<13>C of the earlywood was not significantly correlated to climate data, and that of latewood was correlated to mean temperature of January to September and cummulative rainfall in May to September. In Robinia pseudoacacia, δ^<13>C of the earlywood was correlated to mean temperature of previous January to currernt September, and that of latewood was correlated to mean temperature of previous October to current September and rainfall of previous October to current September. Annual growth rate was higher in Robinia pseudoacacia than Pinus tabulaeformis, but water-use efficiency estimated from δ^<13>C was lower in Robinia than Pinus. From these reslts, Robinia pseudoacacia were supposed to need more water for transpiration than Pinus for its faster growth, thus this species is not recommended to be planted in dry area.