Stoichiometric homeostasis of N:P ratio drives species-specific symbiotic N fixation inhibition under N addition

Qiang Li; Joshua Philp; Matthew D Denton; Yingxin Huang; Jian Wei; Huijuan Sun; Yang Li; Qian Zhao

doi:10.3389/fpls.2023.1076894

Stoichiometric homeostasis of N:P ratio drives species-specific symbiotic N fixation inhibition under N addition

Front Plant Sci. 2023 Apr 26:14:1076894. doi: 10.3389/fpls.2023.1076894. eCollection 2023.

Authors

Qiang Li^{1

2}, Joshua Philp³, Matthew D Denton³, Yingxin Huang^{1

2}, Jian Wei⁴, Huijuan Sun^{1

2}, Yang Li^{2

5}, Qian Zhao⁴

Affiliations

¹ Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China.
² Jilin Provincial Key Laboratory of Grassland Farming, Science and Technology Department of Jilin Province, Changchun, China.
³ School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA, Australia.
⁴ College of Life Sciences, Changchun Normal University, Changchun, China.
⁵ College of Forestry and Grassland Science, Jilin Agricultural University, Changchun, China.

Abstract

Introduction: Symbiotic N fixation inhibition induced by N supply to legumes is potentially regulated by the relative N and P availability in soil. However, the specific responses of different legume species to changes in N:P availability remain unclear, and must be better understood to optimize symbiotic N fixation inputs under N enrichment. This study investigated mechanisms by which soil N and P supply influence the symbiotic N fixation of eight legume species, to quantify the inter-specific differences, and to demonstrate how these differences can be determined by the stoichiometric homeostasis in N:P ratios (H_N:P).

Methods: Eight herbaceous legume species were grown separately in outdoor pots and treated with either no fertilizer (control), N fertilizer (14 g N m^-2), P fertilizer (3.5 g P m^-2) or both N and P fertilizer. Plant nutrients, stoichiometric characteristics, root biomass, non-structural carbohydrates (NSC), rhizosphere chemistry, P mobilization, root nodulation and symbiotic N fixation were measured.

Results: N addition enhanced rhizosphere P mobilization but drove a loss of root biomass and root NSC via exudation of P mobilization compound (organic acid), especially so in treatments without P addition. N addition also induced a 2-14% or 14-36% decline in symbiotic N fixation per plant biomass by legumes in treatments with or without P addition, as a result of decreasing root biomass and root NSC. The changes in symbiotic N fixation were positively correlated with stoichiometric homeostasis of N:P ratios in intact plants without root nodules, regardless of P additions.

Discussion: This study indicates that N addition can induce relative P limitations for growth, which can stimulate rhizosphere P mobilization at the expense of root biomass and carbohydrate concentrations, reducing symbiotic N fixation in legumes. Legume species that had less changes in plant N:P ratio, such as Lespedeza daurica and Medicago varia maintained symbiotic N fixation to a greater extent under N addition.

Keywords: N:P ratio; herbaceous legume; phosphorus mobilization; rhizosphere; stoichiometry; symbiotic N fixation.

Grants and funding

This study was supported by Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA28110300) and Strategic Science and Technology Guide Project of CAS (Grant No. XDA23060403) and Natural Science Foundation of Jilin Province China (Grant No.YDZJ202201ZYTS522) and Natural Science Foundation of China (Grant No. 31600318).