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

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 5 GEP/T), ecosystem WUE (WUE gep 5 GEP/ET or WUE nee 5 NEE/ET) and leaf WUE (WUE l 5 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.

Comparison of evapotranspiration components and water-use efficiency among different land use patterns of temperate steppe in the Northern China pastoral-farming ecotone

“…For determination of ET, compared with the clipping method (CL) used previously (Niu et al 2008;Niu et al 2011), our herbicide method (DS) provided more similar shading and surface roughness conditions to that of the control plots (CK), providing more realistic evaporation and microclimate conditions (Table 2). This DS method provides a more Fig.…”

“…All the plants in this plot withered in 2 days, and the canopy of this treatment was kept standing and dry for the observation period. The aboveground tissue of another plot (CL) in each block was removed by clipping following the procedure used in previous studies (Chen et al 2009b;Niu et al 2011). The third plot was the control plot (CK) without any treatment.…”

“…Details about these static-chamber flux calculations can be found in the calculation procedure in the LI-6400 manual (LiCor Inc. 2004). This static-chamber method has been used and validated in previous studies (Huxman et al 2004;Niu et al 2011). Following measurement of NEE in CK treatments, the chamber was vented, replaced on each frame, and covered with an opaque cloth.…”

“…The vapor and carbon exchange rate of ecosystems or earth surfaces was measured by a cubic chamber (50 cm× 50 cm×50 cm) attached to an infrared gas analyzer (IRGA; LI-6400, LiCor, Lincoln, NE, USA) (Niu et al 2011). Two small fans were fixed inside the top of the chamber to mix air during measurement.…”

“…Following measurement of NEE in CK treatments, the chamber was vented, replaced on each frame, and covered with an opaque cloth. Then, the CO 2 exchange measurements were repeated, with light (and hence photosynthesis) eliminated, to obtain values representing ecosystem respiration (Niu et al 2011. The difference between NEE and Re was considered to represent instantaneous GEP for the ecosystem within the chamber.…”