Effects of Ca2+ on acid tolerance of Medicago sativa and Rhizobium meliloti
钙离子对紫花苜蓿及苜蓿根瘤菌耐酸能力的影响

Soil acidity is an important environmental factor hampering the effective symbiotic nitrogen fixation of Rhizobium meliloti and its host plant Medicag sativa. The study on the effects of Ca2 + on the acid tolerance of M. sativa and R. meliloti showed that applying 5 and 10 mmol . L(-1) of Ca2+ could promote the growth of R. meliloti and advance its log growth phase. Under neutral pH condition, applying Ca2+ didn't have any significant effects on root hair deformation, while under low pH condition, Ca2+ demonstrated positive functions. The higher the Ca2+ concentration, the more significantly it affected, indicating that Ca2+ might play an important role in the recognition between R. meliloti and its host plant. Applying Ca2+ under low pH made the nodulation ahead of time and the nodulation rate enhanced. Definite concentration of Ca2+ could increase the number of nodules in the same period, which was more obvious at anaphase stage or under lower pH condition.