Abstract Description

The depletion of soil organic carbon (C) stocks and accelerated erosion are rapidly reducing the availability of productive agricultural land worldwide, posing a significant threat to global food production capacity. This challenge is particularly acute in Sub-Saharan African (SSA) soils. Integrating specific root traits into wheat cultivars can enhance soil productivity and the sustainability of wheat production by allowing the plants to control key soil biochemical processes, such as carbon (C) turnover. This study aimed to identify beneficial root traits in wheat landrace varieties for potential integration into modern breeding programs. We present here the results of the 2022-2023 trial conducted at the Brits Experimental Farm (ARC-South Africa). This analysis focused on the impact of wheat cultivars on rhizosphere microbiome composition, C turnover dynamics, and the corresponding effects on soil structure, quantified via aggregate stability. As part of the WISHROOTS (Wheat Improving Soil Health through Root Traits) project, parallel field trials were conducted across seven countries from 2022 to 2024, screening 20 wheat cultivars for their potential to improve soil health. Soil sampling was performed at the flowering stage. Aggregate stability was determined using wet sieving. Particle analysis of the experimental soil indicated a composition of 34% clay and 64% sand. Rhizosphere soil samples were analysed for microbiome composition using 16S and ITS amplicon sequencing, performed by Biome Makers Inc. Results from the first field trial (2022-2023) in Pretoria demonstrated an increased ratio of Basidiomycetes to Ascomycetes in the rhizosphere of historic landraces compared to modern cultivars. This fungal shift was correlated with a decrease in the ratio of C respiration to C fixation functions. While both Basidiomycetes and Ascomycetes are key organisms in the degradation of wood, plant, and animal material, Ascomycetes are generally considered more significant degraders of plant biomass in compromised environmental systems, such as agricultural land. We hypothesize that historic landraces preferentially recruit fungi that facilitate longer residence times for recalcitrant carbon (C) in the soil. Although no significant difference in aggregate stability was found among the cultivars assayed during this first trial, an improvement in soil stability is anticipated after the second trial for soils impacted by historic landraces. Historic landraces influenced the microbial community, which in turn affected soil aggregates, although this effect was not statistically significant in the first trial. Macroaggregates constituted the dominant size fraction. In conclusion, the planting of wheat generally exhibits a positive effect on the soil, marked by favorably altered microbial communities and improved soil structure.