Effects of Nitrogen Forms on Root Morphology and Nitrogen Accumulation in Pinus tabuliformis carr. Seedlings under Exponential Fertilization

Abstract

In this study, the effects of different fertilization methods and nitrogen forms on the root morphology and nitrogen accumulation of Pinus tabuliformis carr. were investigated, and the interaction mechanism between roots and nitrogen fertilizer was analyzed to provide a theoretical basis for the rational fertilization of Pinus tabuliformis. The total amount of nitrogen fertilizer applied to seedlings was 100 mg·plant−1; four nitrogen form treatments of ammonium nitrogen, nitrate nitrogen, ammonium nitrate 1:1, and amide nitrogen were set up; and two fertilization methods of conventional and exponential fertilization were applied, with a total of eight experimental treatments. By measuring root parameters, plant biomass, and nitrogen accumulation, the correlation between fertilization method and nitrogen form on the root index of seedlings was analyzed, and the effects of fertilization methods and nitrogen forms on the root growth of seedlings were discussed. Compared with conventional fertilization, exponential fertilization significantly promoted root growth and development, and amide nitrogen was the best nitrogen form. The total length, total surface area, total volume, average diameter, root tips, root/shoot ratio, root tissue density of seedlings’ roots, biomass, and nitrogen accumulation of seedlings in exponential fertilization with amide nitrogen EF3 treatment all increased substantially compared with the others, The effects of fertilization mode, nitrogen form, and their interaction on the partial growth of Pinus tabuliformis seedlings were significant (p < 0.05). The correlation analysis of each index showed that the correlation between nitrogen accumulation and biomass was strongest. Therefore, considering the morphological and structural characteristics of the root system and the nitrogen accumulation in the root system, amide nitrogen in the experimental fertilization can better promote the growth and development of the root system of seedlings.