Environmental variables, including soil water content (SWC), act as constraints on crop growth and productivity. Therefore, open air (E 0), perforated (E 1) and non-perforated (E 2) plastic housings were used with well-watered (W 0), moderately-watered (W 1) and water-stressed (W 2) bush bean plants to explore the relationships between water use efficiency (WUE), carbon isotope discrimination (Δ) and isotopic composition (δ p), leaf assimilation rate (A) and leaf Kjeldahl nitrogen (N) under

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... rse environments. The CO 2 concentration and air carbon isotopic composition (δ a) varied with the environment. The δ a values were reduced by about 0.8 × 10-3 and 3.8 × 10-3 in E 1 and E 2 , respectively, compared with that in E 0. SWC significantly affected WUE, Δ, δ p in both E 0 and E 1 but not in E 2. The decoupling of plants from the outside atmosphere might have contributed in maintaining the above quantities almost constant in E 2. The Δ-value increased by about 2.2 × 10-3 in E 0 and 1.7 × 10-3 in E 1 compared with E 2. Water stress reduced the Δ-value by about 1.1 × 10-3 in both E 0 and E 1. WUE and Δ were significantly correlated in E 0 and E 1 (r =-0.72, and-0.75, respectively) whereas there was no definite relationship between WUE and Δ in E 2 indicating that stomatal conductance was almost independent of SWC. The N-content had little effect on Δ. Leaf N significantly increased in water-stressed plants depending upon the time of harvest and the environment. The mean leaf assimilation rate was significantly higher in E 0 than in either E 1 or E 2 .