Effects of Fulvic Acid Organic Fertilizer on the Growth of Robinia pseudoacacia Seedlings Under Salt Stress

Through the pot experiment, the effects of fulvic acid organic fertilizer on seedling survival rate, relative growth rate, maximum net photosynthetic rate, leaf water content, biomass distribution and root system of Robinia pseudoacacia were studied under different soil salt stress. The results show that compared with low salt, the survival rate of R. pseudoacacia seedlings decreases by 35%, the relative growth rate decreases by 9.6%, the leaf biomass ratio decreases by 7.2%, the specific root surface area decreases by 5.4%, and the stem biomass ratio increases by 3.8%. With adding fulvic acid and increasing fertilizer levels, the relative growth rate, leaf water content and maximum net photosynthetic rate increase firstly and then decrease, the maximum reaches at 4.67g/pot, the maximum values under low salt stress are 4.12×10⁻³mg/(g·d), 11.47μmol/(m²·s) and 69.7%, respectively, and the maximum values under high salt stress are 2.21×10⁻³mg/(g·d), 10.01μmol/(m²·s) and.67.7%, but specific root length increased gradually. Relative growth rate is significantly positively correlated with leaf biomass ratio, maximum net photosynthetic rate, leaf water content, but significantly negatively correlated with stem biomass ratio. Leaf water content is significantly positively correlated with maximum net photosynthetic rate. Therefore, adding organic fertilizer with fulvic acid can alleviate the physiological drought under salt stress, and improve the growth of R. pseudoacacia seedlings by increasing the leaf water content and increasing the maximum net photosynthetic rate and relative growth rate.