Effects Of Potassium Nutrition On Amino Acid Accumulation And Metabolism In Vegetable Soybean And Grain Soybean

Adequate potassium nutrient can not only improve soybean yield but also increase its grain amino acid content,which is a key practice to improve soybean production and quality.However,the mechanism of potassium fertilizer in promoting the accumulation and metabolism of amino acids in vegetable soybean is still rarely reported.Two-year pot experiment with two vegetable soybean cultivars(Zhongkemaodou 1 and Line 121),and one grain soybean cultivar Dongsheng 7 was conducted based on the normal rates of normal nitrogen and phosphorus fertilizer application,under three potassium(K)fertilization treatments.The K treatments included: No K application(K0),120 kg K2SO4 ha-1 at seeding(K1),and 120 kg K2SO4 ha-1 at seedling + 1% K2SO4 foliar application at flowering(K2).The changes of enzyme activity in different parts of soybean in relation to amino acid accumulation and their responses to K application were investigated to understand partial mechanism invloved by K nutrition on amino acid acccumation in vegetable soybean.The results showed that: potassium application increased the nitrogen accumulation in both types of soybeans.The amount of nitrogen accumulation under different fertilization treatments was in the order of K2>K1>K0,and the amount of nitrogen accumulation in each part was in the order of seed > leaf > stem.The potassium application had more prominent effect on seed nitrogen accumulation in vegetable soybean than that of grain soybean.Stem nitrogen accumulation in grain soybean was significantly increased by potassium application,while the responses varied between vegetable soybean cultivars.The activities of nitrate reductase(NR),glutamine synthetase(GS),glutamate synthase(GOGAT)and GS and GOGAT in the leaves of two types of soybean were significantly increased by K application.The effects of foliar potassium application further enhanced their activities,but the responses varied between the two types of soybean.The activity of NR in leaves of vegetable varieties was significantly higher than that of non-potassium treatments at 28 to 42 days after flowering,but no significant differences were found at 42 ~ 56 days after flowering.The effect of foliar potassium application on the NR activity of vegetable soybean varieties was better than that of the grain soybean varieties,but the difference beween the vegetable varieties was not significant.K2 treatment significantly increased GS activities in leaves and grain,and the effects were more prominent to vegetable soybean.Potassium application was beneficial to increase the activity of GOGAT in the leaves of two types of soybean,and no significant differences were found from 49 ~ 56 days after flowering.The GOGAT activity in vegetable soybean grain was increased by K application from 49-56 days after flowering,but its activity was not affacted by K application to grain soybean.The effect of 120 kg · hm-2 potassium fertilizer application significantly increased the total amount of amino acids in vegetable soybean seeds,and the effect was better than that of grain soybean seeds.The foliar potassium application could help further increase the total amino acid content for the two types of soybean,and the total amount of amino acids in the two types of soybean seeds was K2> K1> K0 under different treatment conditions.