Mesorhizobia strain and chickpea variety drive phenotypic plasticity of plant growth and nodulation

Chickpea (Cicer arietinum) establishes symbiotic relationships with several Mesorhizobium species and the three-way interaction between chickpea variety, Mesorhizobium strain, and environment, drives plant growth and nitrogen fixation. Here we quantified the phenotypic plasticity for shoot dry weight, nodule dry weight, nodules per plant, nodule colour, symbiotic effectiveness, and nitrogen cost in a factorial experiment combining five chickpea varieties, seven Mesorhizobium strains and three photothermal regimes. Plant growth and nitrogen fixation traits varied with variety, Mesorhizobium strain, photothermal environment and their interaction. Phenotypic plasticity was larger for nodules per plant (7.3-fold) than for shoot dry weight (2.7-fold), verifying a hierarchy of plasticities between these traits. Strain-driven plasticity of plant growth and nitrogen fixation traits was larger than variety-driven plasticity for our combination of varieties, strains, and photothermal environments, with strain-driven phenotypic plasticity being 2.7-fold vs 1.4-fold for shoot dry matter, 2.5-fold vs 1.7-fold for nodule dry weight, 7.3-fold vs 2.1-fold for nodules per plant, 3.7-fold vs 1.7-fold for nodule color, 2.9-fold vs 1.6-fold for symbiotic effectiveness, and 2.3-fold vs 1.6-fold for nitrogen cost. Our study provides insights on the phenotypic plasticity of the legume-rhizobia interaction by considering the plants as part of the rhizobia environment and vice-versa.