Abstract: Rhizobia can enhance the nitrogen-fixing capacity of alfalfa （Medicago sativa） and improve its stress resistance under abiotic stress. In this study， ‘Xinjiang Daye’ alfalfa （Medicago sativa ‘XinjiangDaye’） and rhizobia Dangeard 1926 were used as materials， and -0.6 MPa PEG-6000 was applied to simulate drought stress， aiming to investigate the effects of different drought durations on the phenotype， physiology， and nitrogen-fixing capacity of alfalfa after rhizobia inoculation. The results showed that with the prolongation of drought stress， the plant height， aboveground biomass， relative leaf water content， root activity， and chlorophyll （a+b） content of alfalfa decreased significantly. However， the contents of amino acids （Phenylalanine， Methionine， Glutamic acid， Tyrosine， Cysteine， Serine， and Aspartic acid）， Malondialdehyde （MDA）， free proline， and the activities of superoxide dismutase （SOD） and catalase （CAT） increased significantly， and the most pronounced effect was observed under stress at day 15 （D₁₅）. At D₁₅， compared with the rhizobia-inoculated treatment （R） without drought stress， the number of root nodules per plant， single nodule weight， and nitrogenase activity in the rhizobia-inoculated treatment under drought stress （GR） decreased by 33.33%， 23.47%， and 58.03%， respectively （P<0.05）. However， compared with the drought-only treatment （G）， the GR treatment significantly increased plant height， aboveground dry weight， SOD activity， and CAT activity by 53.42%， 36.40%， 35.24%， and 11.66%， respectively （P<0.05）， while significantly reducing MDA content by 13.71%. In conclusion， although drought stress inhibited the nitrogen-fixing capacity of alfalfa compared with non-stressed conditions， inoculation with rhizobia under drought stress could enhance the drought resistance of alfalfa plants.

Key words: Drought stress, Alfalfa, rhizobium, Nitrogen-fixation capacity, Drought-resistant ability

摘要： 根瘤菌能够增强紫花苜蓿的固氮能力，同时提升其在非生物胁迫下的抗逆性。本研究以‘新疆大叶’紫花苜蓿（Medicago sativa ‘XinJiangDaYe’）和根瘤菌Dangeard 1926为材料，采用-0.6 MPa PEG-6000模拟干旱胁迫，旨在探究不同干旱时间（干旱处理第7，11，15天分别记为D₇，D₁₁和D₁₅）对接种根瘤菌后紫花苜蓿表型、生理和固氮能力的影响。研究发现，随着干旱时间的延长，紫花苜蓿的株高、地上生物量、叶片相对含水量、根系活力和叶绿素（a+b）含量显著下降，然而氨基酸含量（苯丙氨酸、甲硫氨酸、谷氨酸、酪氨酸、半胱氨酸、丝氨酸以及天冬氨酸）、丙二醛含量、游离脯氨酸含量、超氧化物歧化酶和过氧化氢酶活性显著提高，且在D₁₅胁迫效应最显著。在D₁₅时，与接菌处理（R）相比，干旱条件下接菌处理（GR）的单株根瘤数量、单颗根瘤重量及固氮酶活性分别降低了33.33%，23.47%和58.03%（P<0.05），但与干旱处理（G）相比，GR处理的株高、地上干重、超氧化物歧化酶和过氧化氢酶活性分别提高了53.42%，36.40%，35.24%和11.66%（P<0.05），同时丙二醛含量显著降低了13.71%。综上，虽然与非干旱胁迫相比，干旱胁迫会抑制紫花苜蓿的固氮能力，但是干旱条件下接种根瘤菌可增强紫花苜蓿植株抗旱能力。

关键词: 干旱胁迫, 紫花苜蓿, 根瘤菌, 固氮能力, 抗旱能力