Abstract Climate change profoundly affects the water‐carbon flux balance in forest ecosystems. Intrinsic water use efficiency (iWUE) in trees serves as a key indicator of their water‐carbon trade‐off; however, the differences in iWUE among conifer species and their response mechanisms to environmental changes require further investigation. To address this, this study analyzed the variation patterns of iWUE from 1901 to 2008 for four conifer genera, Pinus , Picea , Abies , and Juniperus , based on tree‐ring stable carbon isotope series from 43 sampling sites across China. The results show that iWUE in Juniperus (104.72 ± 8.38 μmol·mol −1 ) was significantly higher than in Picea (93.94 ± 5.97 μmol·mol −1 ), Pinus (84.88 ± 4.52 μmol·mol −1 ), and Abies (80.84 ± 7.28 μmol·mol −1 ), and its iWUE growth rate also exceeded that of the other three conifer genera. Atmospheric CO 2 concentration was the main driver of the increase in iWUE across all conifers, with Picea and Abies showing active stomatal regulation in response, while Juniperus exhibited weak stomatal responsiveness. Furthermore, the correlations between iWUE and climatic factors were generally stronger in Picea and Pinus than in Abies and Juniperus . Our findings suggest that the influence of atmospheric CO 2 and vapor pressure deficit on tree physiological processes may outweigh the inherent differences in stomatal regulation strategies among species.
Qin et al. (Wed,) studied this question.