The amount of $\text{CO}_2$ assimilated by photosynthesis divided by amount of water transpired by transpiration process is known as}
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Due to their carbon-concentrating mechanisms, C4 plants have higher water use efficiency (typically $300\text{--}400$) than C3 plants ($600\text{--}1000$), while CAM plants have the highest WUE ($50\text{--}100$).