Substitution indexes of carbon isotope discrimination for alfalfa in arid area of central Ningxia

In order to study the substitution indexes of carbon isotope discrimination for alfalfa, ten varieties of alfalfa materials were planted under three water conditions, including severe drought stress (with 0 mm irrigation), moderate drought stress (with 302 mm irrigation) and well watered (with 562 mm irrigation), in arid area of central Ningxia. Relationships betweer Δ13C(carbon isotope discrimination) and ash content, specific leaf dry weight, leaf relative water content, photosynthetic gas exchange parameters in leaf and whole plant were studied at the beginning of flowering stage and flowering stage. The results showed that there was significant effect of water treatment on leaf and whole plant Δ13C, leaf ash content, specific leaf dry weight and photosynthetic gas exchange parameters. Specific leaf dry weight and whole plant Δ13C were negatively correlated under severe drought stress. Leaf relative water content was positively related with whole plant Δ13C under severe drought stress and moderate drought stress. Negative correlation between ash content and whole plant Δ13C was observed under severe drought stress and moderate drought stress.It was accordingly concluded that specific leaf dry weight, leaf relative water content and whole plant ash content might be considered as the substitution indexes of carbon isotope discrimination to predict transpiration efficiency of alfalfa under water limited condition in arid area of Ningxia.