Physiological Characteristics of Medicago sativa L. in Response to Acid Deposition and Freeze-Thaw Stress

Abstract

Acid deposition and temperature variation could lead to changes of physiological characteristics of plants in response to stress. In this paper, Medicago sativa CV. Dongmu–1 was investigated to test the effects of freeze-thaw circle and acid deposition upon the changes of osmotic adjustment substances, biological membrane permeability, and antioxidant enzymes. The experiment was conducted under laboratory conditions, and the seedlings were divided into four groups (group I: no treatment, group II: acid stressed only, group III: freeze-thaw stressed only, group IV: both freeze-thaw and acid stressed). Results indicated that under freeze-thaw circle and acid deposition, the contents of malondialdehyde (MDA) and proline increased respectively by 0.6~203.4 and 19.3~68.8% when compared with group I, while protein content declined by 4.1~31.7%, and the effects were even significant than freeze-thaw-only stressed groups. In the freeze-thaw process, superoxide dismutase (SOD) activity dropped at first and then increased with the increase of temperature, peaking at − 3 °C by 1118.45 U g−1; peroxidase (POD) activity showed a brief rise and declined rapidly below 0 °C. By increasing the potentials of antioxidant enzymes and MDA, the membrane lipid peroxidation inside alfalfa was prevented; meanwhile, several indexes changed adaptively in resisting hurts. Variation of SOD and POD was induced by the defense mechanism, which showed alfalfa’s satisfactory cold resistance and acid tolerance. Further research on acid deposition and freeze-thaw circle would be beneficial for the global cultivation of forage grass.