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

Zhu, Lin; Gao, Xue; Su, Ying; Xu, Xing

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

2019

Zhu, Lin | Gao, Xue | Su, Ying | Xu, Xing

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.

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