Ontogenetic changes in water-use efficiency (δ13C) and leaf traits differ among tree species growing in a semiarid region of the Loess Plateau, China

On the Loess Plateau, China, several planted tree species such as Populus hopeinsis and Robinia pseudoacacia suffer occasional diebacks in the top shoots, reducing growth rates after maturation. However, this does not usually occur in other species, e.g., Ulmus pumila and Zizyphus jujuba. We compared stable carbon isotope ratios (delta C-13) as indicators of leaf water-use efficiency (WUE), leaf mass per unit area (LMA), and leaf area- and mass-based nitrogen content (N-area and N-mass) by tree height (1, 5, and 10 m) in P. hopeinsis, R. pseudoacacia, U. pumila, and Z jujuba. In P. hopeinsis and R. pseudoacacia, leaf delta C-13 and N-area were significantly lower in 10-m trees than in 1-m saplings, indicating that leaf WUE and photosynthetic rates of both species decreased with tree height. In contrast, delta C-13 in Z. jujuba varied little with tree height. The delta C-13 of 10-m-tall U. pumila trees was significantly higher than that of 1-m plants, demonstrating an increase in WUE with tree height. Decreasing WUE, leaf N-area and N-mass with height increases in P. hopeinsis and R. pseudoacacia may be related to water and nutrient limitations for these species in semiarid regions. in contrast, stable or increasing delta C-13 with tree height in U. pumila and Z jujuba may account (to some extent) for successful production of these species under identical environmental conditions. Diameter growth rate also decreased with maturity in P. hopeinsis and R. pseudoacacia, but increased or was stable for U. pumila and Z. jujuba. The differences in leaf WUE and LMA among species with tree maturity may be related to species' growth patterns and susceptibility to drought stress, and are likely to be important new criteria for plantation species selection on the Loess Plateau. (C) 2009 Elsevier B.V. All rights reserved.