Water use efficiency of eight woody species in Liupan Mountains of Ningxia, China

The water use efficiency(WUE) of leaves of 8 dominant tree species was measured from June to September in 2010 in two small watersheds(Xiangshuihe with semi-humid climate and rich tree species, Diediegou with semi-arid climate and few tree species) of Liupanshan Mountains, Ningxia, northwest China, with the objective of recognizing the difference in leaf WUE among species, moisture habitats and seasons. The results showed that the order of mean WUE among the 8 tree species measured at Xiangshuihe watershed is: Pinus Tablaeformis Prunus davidiana Hippophae rhamnoides Quercus liaotungersis Larix principis-rupprechtii Pinus Armandii Tilia panciostata Betula Platyphylla. There was also a significant difference in leaf WUE among the life forms of trees, with the sequence of shrubs small arbor high arbor evergreen conifers deciduous conifers deciduous broadleaved trees. The seasonal variation of leaf WUE of all 8 tree species was presented as decreasing with time during the growing season, however, the variation range is different among tree species. For the 3 tree species(H. rhamnoides, P. davidiana and L. principris-rupprechtii) which were measured at both watershed, their WUEs were kept always higher at the dryer site(Diediegou) than the wetter site(Xishangshuihe), i.e. the former is at least 2.03 times of the latter, showing a very significant(P 0.01) difference between the moisture habitats. Besides the 3 tree species mentioned above, the tree species of P. tablaeformis showed also a higher WUE in drought season. Thus, it can inferred that the 4 tree species must have higher drought-resistance and water-saving property, and can be used as the main tree species for afforestation in dry regions. This study indicated that the WUE of tree species posses both conservativeness and variability with environment; implying for the forestry practice that the WUE of trees can be increased within certain range through a rational training in drought environment.