Abstract
<title>Abstract</title> <p>Aims Grain legumes such as pea are key components of low-input agroecological systems because they rely on symbiotic N₂ fixation to meet their nitrogen (N) demand. However, water deficit (WD) and sulfur (S) deficiency increasingly constrain pea production. We investigated the individual and combined effects of these stresses on growth, nodulation, root system architecture, and nutrient acquisition. Methods Two contrasting pea genotypes, the drought-sensitive Caméor and the drought-resilient Kayanne, were grown exclusively on symbiotic N₂ fixation. Plants were cultivated on a non-destructive phenotyping platform under control, WD, S deficiency, or combined stress conditions, and a structural–functional analysis of pea responses was performed. Results WD reduced biomass by 30%, decreased leaf N and S concentrations, increased carbon concentration and the root-to-shoot ratio, and impaired nutrient uptake more strongly than S deficiency. By contrast, S deficiency reduced biomass only in Kayanne but modified root architecture in both genotypes, increasing shallow-root density and stimulating root elongation in Caméor. Root growth was maintained under all stress conditions, with greater allocation to nodulated roots. Nodule size and biomass declined, reducing plant N content, although N₂-fixation efficiency was unaffected. Kayanne responded to stress by initiating more nodules, whereas Caméor showed increased nodule senescence. Under combined stress, WD largely overrode the effects of S deficiency, including on molybdenum uptake. Conclusions Overall, WD was the dominant constraint during vegetative growth, while the contrasting adaptive strategies of Caméor (root architectural plasticity) and Kayanne (enhanced nodulation) identify complementary traits for breeding pea varieties resilient to multiple abiotic stresses.</p>