Soil water availability and capacity of nitrogen accumulation influence variations of intrinsic water use efficiency in rice

Leaf intrinsic water use efficiency (WUEi) coupling maximum assimilation rate (A(max)) and transpirable water lost via stomatal conductance (g(sc)) has been gaining increasing concern in sustainable crop production. Factors that influence leaf A(max) and WUEi in rice (Oryza sativa L. cv Unkang) at flooding and rainfed conditions were evaluated. Positive correlations for leaf nitrogen content (N-m) and maximum carboxylation rate (V-cmax), for nitrogen allocation in Rubisco enzymes and mesophyll conductance (g(m)) were evident independent of cropping cultures. Rainfed rice exhibited enriched canopy leaf average N-m resulting in higher A(max), partially supporting improved leaf WUEi. Maximum WUEi (up to 0.14 mu mol mmol(-1)) recorded in rainfed rice under drought conditions resulted from increasing g(m)/g(sc) ratio while at cost of significant decline in A(max) due to hydraulically constrained g(sc). A(max) sensitivity related to g(sc) which was regulated by plant hydraulic conductance. WUEi was tightly correlated to V-cmax/g(sc) and g(m)/g(sc) ratios across the paddy and rainfed not to light environment, morphological and physiological traits, highlighting enhance capacity of N-m accumulation in rainfed rice with g(sc) at moderately high level similar to paddy rice facilitate optimization in A(max) and WUEi while, is challenged by drought-vulnerable plant hydraulic conductance. (c) 2016 Elsevier GmbH. All rights reserved.