Effects of Diverse Microclimates and Soil Water Contents on Water-Use Efficiency and Carbon Isotope Discrimination for Bush Bean

Environmental variables, including soil water content (SWC), act as constraints on crop growth and productivity. Therefore, open air (E0), perforated (E1) and nonperforated (E2) plastic housings were used with well-watered (W0), moderately-watered (W1) and water-stressed (W2) bush bean plants to explore the relationships between water- use efficiency (WUE), carbon isotope discrimination (Δ) and isotopic composition (δp), leaf assimilation rate (A) and leaf Kjeldahl nitrogen (N) under diverse environments. The CO2 concentration and air carbon isotopic composition (δa) varied with the environment. The δa values were reduced by about 0.8 × 10-3 and 3.8 × 10-3 in E1 and E2, respectively, compared with that in E0. SWC significantly affected WUE, Δ, δp in both E0 and E1 but not in E2. The 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 × 10-3 in E0 and 1.7 × 10-3 in E1 compared with E2. Water stress reduced the Δ-value by about 1.1 × 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 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