[Effects of CO concentration and soil water content on short-term water-use efficiency at whole-plant level].

Uncovering the variations of short-term water-use efficiency (WUE) at whole-plant level in response to CO concentration () and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, saplings were cultured in simulated climate chambers.There were totally 15 treatments, including of 400 (), 600 () and 800 () μmol·mol and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUE was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h) and nighttime transpiration rates (0.01-0.16 mol·h) at whole-plant level reached the maximum at ×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h) reached the maximum at ×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h) increased with increasing SWC, but decreased with increasing of , reaching the maximum at ×95%-100%FC. For WUE (5.37-24.35 mmol·mol), it reached the maximum at ×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUE when the canopy structure was similar.