Trade‐Offs and Synergies Among Grain Yield and Water Use Efficiency for Climate Change Mitigation and Soil Fertility Rehabilitation in Wheat Production?

Selecting crop genotypes that optimally balance grain yield, water‐use efficiency and belowground carbon allocation is increasingly critical to mitigate climate change, water scarcity and soil degradation while sustaining food production. Although grain yield, water‐use efficiency and belowground carbon allocation have been widely studied as target product profiles or breeding goals, their interactions and potential trade‐offs have rarely been evaluated simultaneously. The objective of this study was to identify wheat genotypes that achieve the best functional compromise between productivity, drought adaptation and climate change mitigation. Ten genetically contrasted wheat genotypes, a subset of 100 previously assessed, were evaluated under water‐stressed (ST = 25% field capacity) and well‐watered (WW = 75% field capacity) conditions in a greenhouse environment using a randomized complete block design with two replications. Measured traits included grain yield (GY), shoot biomass (SB), root biomass (RB), root‐to‐shoot ratio (R:S), plant carbon content and stocks and carbon inputs to the soil assessed using 13 C pulse labelling. Grain yield showed substantial variability (coefficient of variation, CV = 53%), ranging from 171 to 815 g m −2 . Water‐use efficiency for grain yield ranged from 0.14 to 1.52 g L −1 , with the highest variability among measured traits (CV = 77%). Plant carbon stocks ranged from 737 to 3400 g C m −2 (CV = 51%). Soil 13 C excess exhibited high variability (CV = 149%), reflecting low carbon allocation to soils under water‐stressed conditions. Water use efficiency for grain yield (GYw) was strongly correlated with plant biomass ( r = 0.96) and plant carbon stocks ( r = 0.93). Soil 13 C enrichment correlated most strongly with plant biomass ( r = 0.63) and plant carbon stocks ( r = 0.64). The Pareto‐optimal genotype was LM75, with an unweighted multi‐trait index combining GYw, plant carbon stocks, and soil 13 C allocation of 0.90, followed by BW140 (0.78) and LM70 (0.73). Overall, the results demonstrate substantial genetic variation in wheat for grain yield, biomass allocation and soil carbon transfer and highlight the key role of environmental conditions in determining whether plant carbon allocation generates trade‐offs or synergies between agricultural productivity and soil biogeochemical processes. These findings provide a foundation for breeding strategies targeting genotypes that reconcile high productivity with improved water‐use efficiency and enhanced soil belowground carbon allocation, thereby advancing climate change mitigation and long‐term soil restoration and driving agricultural productivity.