Effects of diverse microclimates and soil water contents on water-use efficiency and carbon isotope discrimination for bush bean

Environmental variables including soil water contents (SWC) act as constraints to crop growth and productivity. Therefore, open air (E₀), and perforated (E₁) and non-perforated (E₂) plastic housing environments were used with well-watered (W₀), moderately-watered (W₁), and water-stressed (W₂) bush bean plants to explore relationships between water-use efficiency (WUE), carbon isotope discrimination (Δ) and composition (d_p), leaf assimilation rate (A) and leaf Kjeldahl nitrogen (N).   CO₂ concentration and the air carbon isotope composition (d_a) varied with the environment. The d_a values were reduced by about 0.8 x 10^-3 and 3.8 x 10^-3 in E₁ and E₂, respectively, compared with that in E₀.  SWC significantly affected WUE, d_p and Δ in E₀ and E₁ but not in E₂. Decoupling of plants from the outside atmosphere might have contributed in maintaining the above quantities almost constant in E₂. The Δ-value increased by about 2.2 x 10^-3 in E₀ and 1.7 x 10^-3 in E₁ compared with E₂. Water stress reduced Δ-value by about 1.1 x 10^-3in both E₀ and E₁. WUE and Δ were significantly correlated in E₀ and E₁ (r = - 0.72, and - 0.75, respectively) whereas there was no definite relationship between WUE and Δ in E₂ indicating that here 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 E₀ than in either E₁ or E₂ environment.