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 (E۰), perforated (E۱) and non-perforated (E۲) plastic housings were used with well-watered (W۰), moderately-watered (W۱) and water-stressed (W۲) 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 CO۲ concentration and air carbon isotopic composition (δa) varied with the environment. The δa values were reduced by about ۰.۸  ۱۰-۳ and ۳.۸  ۱۰-۳ in E۱ and E۲, respectively, compared with that in E۰. SWC significantly affected WUE, Δ, δp in both E۰ and E۱ but not in E۲. The decoupling of plants from the outside atmosphere might have contributed in maintaining the above quantities almost constant in E۲. The Δ-value increased by about ۲.۲  ۱۰-۳ in E۰ and ۱.۷  ۱۰-۳ in E۱ compared with E۲. Water stress reduced the Δ-value by about ۱.۱  ۱۰-۳in both E۰ and E۱. WUE and Δ were significantly correlated in E۰ and E۱ (r = - ۰.۷۲, and - ۰.۷۵, respectively) whereas there was no definite relationship between WUE and Δ in E۲ 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 assimila-tion rate was significantly higher in E۰ than in either E۱ or E۲.

کلیدواژه ها:

Bush bean ، Carbon isotope discrimination ، Plastic tunnel ، Water-use efficiency