Relative abundance of ureides differs among plant fractions in soybean

Abstract The present study aims to compare the relative abundance of ureides (RAU) among soybean [Glycine max (L.) Merr.] plant fractions in contrasting trial settings and under three nitrogen (N) rates, designed to create variability on symbiotic N fixation. A greenhouse and a field experiment evaluated the RAU in plant fractions (base of the main stem, petiole and leaflets of the uppermost fully developed leaf) at varying growth stages and under absent, intermediate, or high N fertilization rates. The RAU was determined by measuring dry tissue nitrate and ureides and considered the entire main stem as benchmarking plant fraction, previously calibrated based on 15N isotope methods. The main outcomes of this study were: 1) RAU in the base of the stem accurately reflected the one obtained in the main stem; 2) upper leaflets RAU poorly correlate with the main stem values; and 3) the RAU from the upper petiole presented similar trends as the base of the stem but did not provide as reliable RAU estimation. The base of the stem is a reliable fraction to quantify soybean RAU while simplifying dry mass collection. The upper petiole fraction did not estimate RAU accurately, but it could differentiate contrasting N fixation levels.