Skip to main content
Open Access Publications from the University of California

UC Riverside

UC Riverside Previously Published Works bannerUC Riverside

Lotus japonicus regulates root nodulation and nitrogen fixation dependent on the molecular form of nitrogen fertilizer


Purpose: Legumes form root nodules to gain fixed nitrogen from rhizobia and can also access nitrogen in soil. Data suggest that plants might discriminate among these sources to optimize growth, but recognition of symbiotically fixed nitrogen and its regulation remain poorly understood. Methods: A greenhouse inoculation study manipulated the molecular form and concentration of nitrogen available using two Lotus japonicus genotypes and the nitrogen-fixing symbiont, Mesorhizobium loti. Plants were supplied with sole organic and inorganic nitrogen sources to simulate forms that plants might receive from symbiotic nitrogen fixation or from the soil. Host benefit from and regulation of symbiosis was investigated by quantifying symbiotic trait variation and isotopic analysis of nitrogen fixation. Results: Host growth varied in response to fertilization with alanine, aspartic acid, ammonium, and nitrate, suggesting differences in catabolism efficiency. Net benefits of nodulation were reduced or eliminated under all forms of extrinsic fertilization. However, even when symbiosis imposed significant costs, hosts did not reduce investment into nodulation or nitrogen fixation when exposed to aspartic acid, unlike with other nitrogen sources. Conclusions: L. japonicus can adaptively downregulate investment into symbiosis in the presence of some but not all nitrogen sources. Failure to downregulate any aspect of symbiosis in the presence of aspartic acid suggests that it might be jamming the main signal used by L. japonicus to detect nitrogen fixation.

Many UC-authored scholarly publications are freely available on this site because of the UC's open access policies. Let us know how this access is important for you.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View