Responses Of Sugar Beet Seedings And The Changes Of Rhizosphere Enviroment Under Na₂CO₃ Stress

Sugar beet is one of the main economic crops in the north of China, has strong salt-tolerance, therefore, to study the physiological response of sugar beet seedlings under Na 2CO3 stress and root the change of the surrounding environment, to further excavate beet adaptability to saline soil is of great significance. To study the effect of saline-alkali stress on dry mass,rhizosphere soil enzymes activities and soil microbial quantities,the pot experiments were designed that two sugar beet varieties, KWS0143 and Beta464 were planted in four different Na₂CO₃ concentration（0%, 0.4%, 0.8% and 1.2% of soil） pots,and the fresh, dry weight and root activity of seedlings, soil enzyme activities and amount of microbiology in soil were recorded. to study the activities of SOD, POD and the content of MDA on leaf and root. And on this basis, through the Na₂CO₃ soil quality percentage of 0.4%, 0.5%, 0.6%, 0.7% and 0.8% a few gradient processing, further sugarbeet by defining the initial threshold of Na₂CO₃ intimidation. The main conclusions are as follows:（1） The results showed that seedling emergence decline and fresh, dry weight, root activity and root growth（length, area, volume） of plants increased firstly and then decreased with increasing concentration of Na₂CO₃ stress,and fresh, dry weight, root activity and root growth（length, area, volume） was significantly higher than CK in the 0.4% concentrations of seeding（P<0.05）. And the treatments of 0.8% and 1.2% sharply decreased the fresh,dry weight,root activity and root growth（length,area,volume）（P<0.05）. However KWS0143 stronger than Beta464 under 1.2% treatments.（2） The activities of SOD and POD has the same tends that increased primary stage and then downward, and the highest activities at concentration of 0.4% in leaves and toots. The content of MDA increased and concentration of 1.2% was the highest in leaves and toots. In the same concentration, the activities of SOD and POD with duration of stresses increased firstly and th en decreased. Three weeks after the two pairs of true leaves unfolded,the activities reached highest. But the content of MDA increased slowly after a sharp upward trend over time. However KWS0143 stronger than Beta464 under 1.2% treatments.（3） The results showed that comparing with the control,the dry mass of seedlings was significantly increased in the treatment of 0.4% Na₂CO₃, while that was significantly decreased in the 0.8% and 1.2% Na₂CO₃ treatments and the differences among different treatments were distinct. The soil urease enzyme, alkali phosphatase enzyme and peroxidase enzyme activities in the root rhizosphere of seedlings presented a similar tendency under different concentrations of Na 2CO3. The enzyme activities with the treatment 0.4% Na₂CO₃ was non- significantly enhanced than in the CK while that with the treatment of 0.8% and 1.2% Na₂CO₃ was significantly reduced. All of the soil enzymes activities in KWS0143 were higher than in Beta464. Compared with CK,the treatment of 0.4% Na₂CO₃ did not lead to significant change of soil microbial communities,but the treatment of 0.8% and 1.2% had sharply decreased the amount of soil bacteria,fungi and actinomycets community（P<0.05）. And the amount of rhizosphere soil microbial communities in KWS0143 was higher than in Beta464. Correlation analysis showed that dry mass,soil enzymes and soil microbial of the two varieties was significantly positive correlation（ P<0.01）. Path coefficient analysis indicated the order of determinant coefficient with KWS0143 dry mass as sctinomycetes > bacterias > peroxidase enzyme > urease enzyme > fungis > alkali phosphatase enzyme,and the order of determinant coefficient with Beta464 dry mass as actinomycetes > peroxidase enzyme > urease enzyme > fungis> alkali phosphatase enzyme>bacteria.（4） Under this experimental condition, when the concentration of Na₂CO₃ concentrations greater than 0.6%, the dry weight of root seedlings became obvious drop, shows that 0.6% of Na₂CO₃ treatment concentration is the initial concentration of sugar beet seedlings under stress.