Response and intraspecific differences in nitrogen metabolism of alfalfa (Medicago sativa L.) under cadmium stress

Pot experiments were carried out to evaluate the response and intraspecific differences in nitrogen metabolism of 20 alfalfa cultivars under cadmium stress. To the aim, exogenous cadmium was added into soil with concentration of 0 (control) and 50 mg kg−1. Results showed that 20 alfalfa were ranked as following according to response index: Guochan (550.93) > Deqin (372.50) > Caoyuan No.1 (350.26) > Queen (345.45) > Xinmu No.2 (344.43) > Longzhong (274.85) > Victoria (233.13) > Emperor (233.13) > Giant (192.29) > Qianjing (101.21) > Xinjiangdaye (75.72) > Algonuin (−32.55) > Duoye (−62.44) > Altay (−102.77) > Sandeli (−155.02) > Turist (−193.24) > Gannong No.1 (−199.22) > Sijiwang (−245.14) > Zhongmu No.1 (−245.48) > WL525HQ (−268.26). Guochan was identified as cadmium tolerant cultivar. Compared with the control group, its plant height increased by 40.96%, shoot and root biomass respectively increased by 18.10% and 70.19%, total nitrogen content in shoot and root respectively increased by 26.69% and decreased by 12.59%, nitrate content decreased by 7.05%, content of ammonium, proline, free amino acid and soluble protein respectively increased by 13.67%, 89.63%, 28.09% and 14.86%, activity of nitrate reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase increased respectively 58.52%, 36.63%, 97.79% and 75.44%. WL525HQ, its above indicators appeared significant differences with those of Guochan, was identified as cadmium sensitive cultivar. In conclusion that the nitrogen metabolism process played an important role for alfalfa to adapt cadmium stress, and the response of nitrogen metabolism to cadmium stress varied with different alfalfa cultivars.