Abstract: By determining the CO₂/H₂O gas exchange in winter wheat leaves during its earring to flowering stages under different water supply, this paper dealt with the relationships of water use efficiency (WUE) with photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs), intercellular CO₂ concentration(Ci) and leaf temperature(Tl). The WUE presented a quadratic relation with Pn. It increased to a certain degree with increasing Tr, and then decreased when Tr was higher than a certain value. It decreased remarkably with increasing Ci. The increase of Tl promoted the photosynthesis and transpiration, but when T1 was up to a certain degree, it showed an inhibitory effect on WUE, indicating that in a certain range, the increase of T1 is not beneficial to WUE. With the increase of Gs, WUEreached to a certain high level and then fall down.

Key words: Water use efficiency, Physiological mechanism, Winter wheat, Illumina MiSeq sequencing, landfill cover soil, trichloroethylene, bacterial community structure.