Changes in .sup.15N natural abundance of biologically fixed N.sub.2 in soybean due to shading, rhizobium strain and plant growth stage

• Published in: Plant and soil Vol. 426; no. 1-2; p. 413
• Main Authors: Araujo, Karla E. C, Vergara, Carlos, Guimarães, Ana Paula, Rouws, Janaina R. C, Jantalia, Claudia P, Urquiaga, Segundo, Alves, Bruno J. R
• Format: Journal Article
• Language: English
• Published: Springer 01-05-2018
• Subjects: Growth; Rhizobium; Soybeans
• ISSN: 0032-079X
• DOI: 10.1007/s11104-018-3627-4

Aims The evaluation of .sup.15N abundance of N derived from biological N.sub.2 fixation (BNF) in legume shoots ('B.sub.S' value) is essential for quantifying BNF inputs to field-grown legumes. The aim of this study was to investigate the impact of shading, development stage of soybean (Glycine max) and rhizobium strain on the 'B.sub.S' value. Methods Soybean plants were grown in pots of autoclaved sand/perlite mixture in the open field. Plants were harvested at weekly intervals from 46 days after planting (DAP) to 75 DAP. All material was analysed for N and .sup.15N abundance. 'B.sub.S' was calculated assuming 50% of seed N was translocated to the shoots. Results 'B.sub.S' was stable until 60 DAP but subsequently increased for the three strains tested. Nodule efficiency (N.sub.2 fixed g DM nodule.sup.-1) was greatly increased by shading and was significantly different between Bradyrhizobium species. 'B.sub.S' was greatly increased by shading. Conclusion We recommend that 'B.sub.S' should be evaluated on plants of the same development stage and light intensity as those where BNF is quantified in the field. Different Bradyrhizobium strains make a large impact on 'B.sub.S' and may lead to considerable errors in estimation of BNF inputs to plants with high %N derived from BNF.