| Two Brazilian nitrogen fixing sugarcane varieties B1 and B8 were employed as the plant materials. They were cultured with nutrition solution that contained different levels of Mo i.e. 0mg/L, 0.01mg/L, 0.02mg/L and 0.04mg/L, respectively, in pot trial with sand in greenhouse, and spayed on the plant leaves with different levels of molybdenum acid i.e. 0g/hm2, 300g/hm2, 600g/hm2 and 900 g/hm2, respectively at early tillering stage in field experiment. The physiological and biochemical indexes were measured at different stages, and their correlations with the nitrogen fixation, nitrogen metabolism and photosynthesis were analyzed. The experimental results were as follows:1. Under nitrogenous conditions in the greenhouse, the treatment with lower concentration of Mo promoted the activity of nitrogenase in roots, but the treatment with higher concentration increased the activities in stems of the two sugarcane varieties, as well as in leaves of the variety Bl. The activitiesof Ca~2+-ATPase and Mg~2+-ATPase were enhanced by the treatment with 0.01 mg/L Mo in leaves of Bl at initial elongation stages, and that of B8 at mid elongation stage. All the Mo treatments increased the activity of NR and decreased the NO3-N content compared with the control for both Bl and B8. As a result, the treatment with 0.01 mg/L Mo also increased the activity of GS in B1 after initial elongation stages and that in B8 at young plant stages, and it also decreased the NH4-N content and enhanced the soluble protein so improved the nitrogen metabolism. The treatment with 0.01 mg/L Mo also increased the net photosynthetic rate, the contents of Chlorophyll, soluble sugar and nitrogen in leaves of B1, and that with 0.02mg/L Mo increased those in B8 except for soluble sugar content.2. Under non-nitrogenous conditions in the greenhouse, as compared with the control, all the Mo treatments increased the activity of nitrogenase in leaves and stems of Bl, but decreased that in leaves, stems and roots of B 8 as well as in roots of B1. The activity of Ca2+-ATPase was decreased with the Mo treatments in the two sugarcane varieties, but both the treatments with 0.01 mg/L and 0.02mg/L Mo enhanced the activity of Mg2+-ATPase in B8. After initial elongation stage, the activity of NR was increased and the NO3-N content was decreased in both sugarcane varieties treated with different levels of Mo. Furthermore, the activity of GS and soluble protein content were higher than the control of Bl and the NH4-N content was lower in leaves of B8 at tillering stage. The treatment with 0.01mg/L Mo was more efficient in improving the contents of Chlorophyll, soluble sugar, nitrogen, kalium and the net photosynthetic rate than other treatments. |
