Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level

Abstract

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) μmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.