Soil and genotype-driven resource allocation trade-offs shape root exudation across crop species

Aims: Root exudates play a central role in rhizosphere processes, many of which support plant growth. While increased exudation under abiotic stresses has been frequently linked to enhanced plant resilience, crop- and genotype- and soil-specific exudation patterns under non-stress conditions remain poorly understood. This study aimed to assess how soil type and genotype influence root exudation in major and emerging European crops and to explore how root morphology and plant growth are related to exudation. Methods: Four genotypes each of barley (Hordeum vulgare), faba bean (Vicia faba), potato (Solanum tuberosum), and sweet potato (Ipomoea batatas (L.) Lam.) were grown in three distinct European soils under non-stress conditions. Exudates were collected using a soil-hydroponic-hybrid approach and analysed for dissolved organic carbon and nitrogen, as well as total carbohydrates, amino acids, and phenolic compounds. Biomass and root morphology were assessed to examine correlations with exudation patterns. Results: Results showed that soil type and genotype affected exudation patterns, but their influence varied by crop. Plant growth was negatively correlated with exudation rates across most crops, likely reflecting a trade-off in carbon and nitrogen allocation between biomass accumulation and rhizodeposition. Root morphological traits partly correlated with root exudation rates, but no universal relationships were detected across crops. Conclusion: Our results provide novel insights into belowground resource partitioning and broaden the understanding of exudation patterns to previously underexplored crops, highlighting resource allocation trade-offs shaped by genotype and soil as important drivers of exudation dynamics.