Effects of Different Chemical Forms of Nitrogen on the Quick and Reversible Inhibition of Soybean Nodule Growth and Nitrogen Fixation Activity

Abstract

It has been reported that supply of nitrate to culture solution rapidly and reversibly inhibits nodule growth and nitrogen fixation activity of soybean. In this study, the effects of ammonium, urea, or glutamine on nodule growth and nitrogen fixation activity are compared with that for nitrate. Soybean plants were cultivated with a nitrogen-free nutrient solution, then 1 mM-N of nitrate, ammonium, glutamine, or urea were supplied from 12 DAP until 17 DAP. Repression of nodule growth and nitrogen fixation activity at 17 DAP were observed by ammonium, urea, and glutamine like nitrate, although the inhibitory effects were milder than nitrate. The removal of nitrogen from the culture solutions after nitrogen treatments resulted in a recovery of the nodule growth. It was found that the glutamine treatment followed by N-free cultivation gave highest nitrogen fixation activity about two times of the control. Tracer experiments with 15 N and 13 C were performed to evaluate the translocation of N and C to the different tissues. Culture solutions containing a 15 N-labeled nitrogen source were supplied from 21 DAP, and the whole shoots were exposed to 13 CO 2 for 60 min on 23 DAP, and plants were harvested on 24 DAP. The percentage distribution of 15 N in nodules was highest for ammonium (1.4%) followed by glutamine (0.78%), urea (0.32%) and nitrate (0.25%). The percentage distribution of 13 C in the nodules was highest for the control (11.5%) followed by urea (5.8%), glutamine (2.6%), ammonium (2.3%), and nitrate (2.3%). The inhibitory effects of nitrogen compounds appeared to be related to a decrease in photoassimilate partitioning in the nodules, rather than 15 N transport into the nodules. The free amino acid concentrations after nitrogen treatments were increased in the nodules and leaves by nitrate, in the roots by ammonium, in the stems by urea, and the roots, stems, and leaves by glutamine treatment. The concentrations of asparagine, aspartate, and glutamine were increased after nitrogen treatments. By the long-term supply of nitrogen for 2-weeks, nitrate significantly increased the lateral roots and leaf growth. The long-term supply of urea and glutamine also promoted the lateral roots and leaf growth, but ammonium suppressed them.

Morphological and physiological responses and plasticity in Robinia pseudoacacia to the coupling of water, nitrogen and phosphorus

“…This result may have occurred because excessive nitrogen under drought conditions inhibited RuBP carboxylase activity, which led to the decrease in gas exchange parameters and affected the growth of plants ( Nakaji et al., 2002). Alternatively, because R. pseudoacacia functions in biological nitrogen fixation, it can make more effective use of low‐level nitrogen, but excessive nitrogen may inhibit the nitrogen fixation ability of legumes and thus inhibit plant growth ( Yamashita et al., 2019). In addition, under drought conditions, P deficiency obviously weakened the positive effect of the HN treatment on plant height, stem diameter and biomass, which may be because under the condition of soil water deficiency.…”

Low Nitrogen Fertilization Alter Rhizosphere Microorganism Community and Improve Sweetpotato Yield in a Nitrogen-Deficient Rocky Soil

“…It was suggested that low N fertilization (0.7 g N/m 2 ) may have promoted the growth of N-fixing microorganisms in the N-deficient soil. And (2) the influence on N fixation activity was milder for urea than for nitrate and ammonium (Yamashita et al, 2019).…”

Responses of Swamp Cypress (Taxodium distichum) and Chinese Willow (Salix matsudana) Roots to Periodic Submergence in Mega-Reservoir: Changes in Organic Acid Concentration

“…Primary roots were separated from the laterals root of each plant when collecting samples and immediately transported to the laboratory in an icebox. They were placed in an oven at 110 • C for 15 min after washing with deionized water, then adjusted to 80 • C to dry until constant weight [45,46], and finally ground into a powder then sifted through a 1 mm sieve.…”