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.

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SARS-CoV-2 carries the largest single-stranded RNA genome and is the causal pathogen of the ongoing COVID-19 pandemic. How the SARS-CoV-2 RNA genome is folded in the virion remains unknown. To fill the knowledge gap and facilitate structure-based drug development, we develop a virion RNA in situ conformation sequencing technology, named vRIC-seq, for probing viral RNA genome structure unbiasedly. Using vRIC-seq data, we reconstruct the tertiary structure of the SARS-CoV-2 genome and reveal a surprisingly “unentangled globule” conformation. We uncover many long-range duplexes and higher-order junctions, both of which are under purifying selections and contribute to the sequential package of the SARS-CoV-2 genome. Unexpectedly, the D614G and the other two accompanying mutations may remodel duplexes into more stable forms. Lastly, the structure-guided design of potent small interfering RNAs can obliterate the SARS-CoV-2 in Vero cells. Overall, our work provides a framework for studying the genome structure, function, and dynamics of emerging deadly RNA viruses.