Effects of nitrogen concentrations on nodulation and nitrogenase activity in dual root systems of soybean plants

Abstract

Currently, the mechanisms underlying the effects of nitrogen on nodulation and nitrogen fixation of leguminous plants remain uncertain. To further investigate the relationship between nitrogen with nodulation and nitrogen fixation of soybean plants, a young seedling grafting technique was applied to generate soybean plants with dual root systems. The two root systems were separately cultured in sand medium, with one irrigated with nutrient solution containing NH þ 4 or NO À 3 as nitrogen sources (the N+ side) and another irrigated with nitrogen-free nutrient solution (the N− side). Various nitrogen concentrations, 0, 25, 50, 75, and 100 mg/L, were applied to the N+-side root system to determine the effects of nitrogen concentrations on nodulation and nitrogenase activity of soybean plants. The results showed that in the dual root systems constructed by seedling grafting, the number and weight of root nodules at the N+ side both exhibited a single-peak changing trend of first increasing and then decreasing with nitrogen concentrations. Root nodulation was accelerated by low concentrations of nitrogen (<50 mg/L) and significantly suppressed by high concentrations of nitrogen (>50 mg/L). In contrast, the number and weight of root nodules at the N− side showed a constant increasing trend with the increase in nitrogen concentrations. Taken together, these results indicated that high nitrogen concentration exerts a contact-dependent localized inhibitory effect on the formation (number of nodules) and growth of root nodules (weight of nodules). The nitrogenase activities in the root nodules at both the N+ and the N− sides displayed trends of first increasing and then decreasing with nitrogen concentrations, reaching a single peak when the nitrogen concentration was 50 mg/L. In addition, the promotive or inhibitory effects of nitrogen at different concentrations on nitrogenase activity in the root nodules were synchronous between the N+ and the N− sides, suggesting that the effect of nitrogen is systematically regulated via interactions between the aboveground and underground parts of the plants.

Effect of Azotobacter Application Method on Yield of Soybean (Glycine max (L.) Merill) on Dry Land

“…Jumlah nodula pada semua perlakuan dalam percobaan hanya 4-6 buah. Faktor pembentukan nodula terutama tergantung dari kadar N di tanah (Xia et al, 2017); kemasaman, kelembaban dan suhu tanah (Al Falih, 2002); serta inokulasi Bradyrhizobium (Bhuiyan et al, 2008).…”

“…Nitrogen total di tanah setelah percobaan (Tabel 1) termasuk rendah yang mendukung pembentukan nodula (Xia et al, 2017). Suhu dan kelembaban tanah selama penelitian tidak diukur namun kekeringan dapat meningkatkan suhu dan menurunkan kelembaban yang menurunkan nodulasi (Al Falih, 2002).…”

Genome-wide identification, phylogeny, and expression profiling of RWP-RK gene family under low nitrogen and nodulation in Arabidopsis and legumes

“…Higher efficiency of nitrogen-fixation under 5 mM nitrates than that under 0 mM suggests that appropriately low concentrations of nitrates simulate nodulation by increasing nitrogenase activity or nodule number in P. vulgaris. The stimulation of nodulation by low nitrogen treatment has also been observed in G. max [63]. In Lotus japonicus, the NLP NITRATE UNRESPONSIVE SYMBIOSIS 1 (NRSYM1) is a key regulator of the nitrateinduced control of root nodule symbiosis [47].…”

Peran Eksopolisakarida Azotobacter dan Bahan Organik untuk Meningkatkan Nodulasi dan Biomassa Kedelai pada Dua Ordo Tanah

“…Penambahan pupuk Urea serta kompos kotoran sapi dapat meningkatkan kadar N tanah dan menekan nodulasi. Nitrogen tinggi menghambat pembentukan, jumlah dan bobot nodula karena nodulasi dipercepat oleh nitrogen rendah yaitu <50 mg L -1 (Xia et al, 2017). Nodula berkembang dengan baik dan aktif jika kandungan nitrogen tanah rendah, tanah tidak terlalu masam, meskipun beberapa strain rizobia toleran terhadap kemasaman rendah (Ferguson et al, 2013).…”