Water‐use efficiency in response to climate change: from leaf to ecosystem in a temperate steppe

TLDR

Water‑use efficiency links carbon and water cycling and is key to ecosystem productivity, yet its response to climate change across scales remains poorly understood. We measured leaf, canopy, and ecosystem WUE in a temperate steppe in Northern China from 2005 to 2008 under increased precipitation and warming, using GEP, NEE, ET, and leaf photosynthesis and transpiration to calculate WUE at each level. Precipitation increased canopy and ecosystem WUE but decreased leaf WUE, while warming reduced canopy and ecosystem WUE but left leaf WUE unchanged, indicating scale‑dependent responses that caution against upscaling leaf WUE and informing projections of climate impacts on productivity.

Abstract

Abstract Water‐use efficiency (WUE) has been recognized as an important characteristic of ecosystem productivity, which links carbon (C) and water cycling. However, little is known about how WUE responds to climate change at different scales. Here, we investigated WUE at leaf, canopy, and ecosystem levels under increased precipitation and warming from 2005 to 2008 in a temperate steppe in Northern China. We measured gross ecosystem productivity (GEP), net ecosystem CO 2 exchange (NEE), evapotranspiration (ET), evaporation (E), canopy transpiration ( T c ), as well as leaf photosynthesis ( P max ) and transpiration ( T l ) of a dominant species to calculate canopy WUE (WUE c =GEP/T), ecosystem WUE (WUE gep =GEP/ET or WUE nee =NEE/ET) and leaf WUE (WUE l = P max / T l ). The results showed that increased precipitation stimulated WUE c , WUE gep and WUE nee by 17.1%, 10.2% and 12.6%, respectively, but decreased WUE l by 27.4%. Climate warming reduced canopy and ecosystem WUE over the 4 years but did not affect leaf level WUE. Across the 4 years and the measured plots, canopy and ecosystem WUE linearly increased, but leaf level WUE of the dominant species linearly decreased with increasing precipitation. The differential responses of canopy/ecosystem WUE and leaf WUE to climate change suggest that caution should be taken when upscaling WUE from leaf to larger scales. Our findings will also facilitate mechanistic understanding of the C–water relationships across different organism levels and in projecting the effects of climate warming and shifting precipitation regimes on productivity in arid and semiarid ecosystems.