Relationship of Carbon Isotope Discrimination with Biomass and Water Use Efficiency for Alfalfa in Northwestern China

Abstract

Carbon isotope discrimination (Δ) has been proposed as a method for evaluating transpiration efficiency in C3 plants. It is important to study the association of Δ in different parts with the long‐term water use efficiency (WUE). In this paper, plant height, Δ in leaf water soluble carbohydrates (ΔWSC), photosynthetic gas exchange parameters, Δ in aboveground shoot (ΔAGS), stem/leaf weight ratio, aboveground biomass (AGB), evapotranspiration, and WUE were determined in a collection of 10 alfalfa (Medicago sativa L.) genotypes under three water treatments (230 [T1], 460 [T2], and 700 mm irrigation [T3]) in a Ningxia central desert steppe in 2012 and 2013. Significant interactions were found for AGB and WUE among year, treatment, and genotype, whereas significant interactions of year × treatment and year × genotype were only found for ΔAGS but not for ΔWSC. Generally, more water input increased the values of the traits tested except for WUE and single‐leaf intrinsic WUE (Pn/Gs). More irrigated water input resulted in increase in AGB, ΔAGS, and ΔWSC and decrease in Pn/Gs. The greatest WUE was recorded under T2 in 2012. Significant and positive correlations were observed between AGB and ΔAGS (r = 0.588, 0.574, and 0.386 under T1, T2, and T3, respectively). Under T2 and T3, ΔWSC correlated negatively with WUE (r = −0.383 and 0.602, respectively). Ningmu No. 1 was found to have the greatest WUE (18.34 kg ha−1 mm−1) and yield (17.71 Mg ha−1) across water treatments and years. The findings suggest that in the semiarid areas applying irrigation of 230 to 700 mm yr−1, Δ in aboveground shoots or in leaf water‐soluble carbohydrates at the flowering stage seems to be a useful indicators reflecting aboveground biomass and integrated WUE for alfalfa.

Diurnal and Seasonal Variations of Water Use Efficiency of Rice–Wheat Rotation Cropland in the Jianghuai River Basin of China

“…There are many ways to understand WUE. At the leaf scale, the carbon isotope method had been used to study WUE which was regarded as the ratio of CO 2 assimilation rate to stomatal conductance (Zhu et al 2019). But it was expensive to use isotopes to make extensive and long-term observations.…”