Abstract
High water use efficiency (WUE) is particularly important for the adaptation of plants to their environments when water is limited. The measurement of long-term plant WUE in the field is always difficult and destructive, therefore plant carbon isotope discrimination (Δ) is often used as a time-integrated surrogate estimate of WUE under several assumptions. One of the important assumptions is that the leaf-to-air vapour pressure differences (VPD) are similar among the plants being compared. So far there is lack of experimental data collected under controlled environment on the relationship between WUE and Δ under different VPDs. This study was designed to fill this gap. Seedlings of four conifer tree species (Pinus massoniana Lamb. var. massoniana, Pinus tabulaeformis Carr. var. tabulaeformis, Platycladus orientalis [Linn.] and Cunninghamia lanceolata [Lamb.] Hook) were grown in controlled environment chambers under four different air humidity (VPD of 2.4, 2.0, 1.6 and 1.2 kPa) for 4 weeks. Results showed that there was positive linear relationship between carbon isotope discrimination (Δ) and WUE within each species for two species (P. massoniana and Platycladus orientalis), but no significant relationships for another two species (P. tabulaeformis and C. lanceolata).
