Assessing weed impacts in tropical cropping systems through a functional trait-based approach : a case study on sugarcane

Context Yield losses due to weeds arise from competition for light, water, and nutrients. Beyond abundance, weed impact could also depend on their resource acquisition strategies. This study aims to evaluate how different weed species, characterized by distinct functional traits, may affect sugarcane agronomic performances under varying environmental and management conditions. Methods Two field trials were conducted in Réunion Island (2021 – 2023) under contrasting irrigation and fertilization conditions. Different weed management treatments (unweeded, fully weeded, and selectively weeded) leading to distinct weed communities dominated by climbers, perennials, grasses, or small dicotyledons were compared. Sugarcane growth and yield, and weed ground cover were measured over both cropping seasons. Dominant weed species were characterized by functional traits related to competition for resources. Linear mixed models assessed treatment effects while multivariate analyses (PCA, clustering, RLQ and fourth-corner) were used to group species by traits and link them to crop performance. Results Reduction of sugarcane biomass and stem density was related to weeds to an extent that varied by year and selected weed communities. Weed cover alone did not explain sugarcane biomass reduction. Trait-based groups revealed that climbers exhibited leaf acquisitive and root conservative traits, while dicotyledons showed the opposite pattern. Sugarcane biomass reduction seems mainly related to Climbers due to leaf acquisitive traits under high-input conditions and small dicotyledons due to root acquisitive traits under low-input conditions. Conclusions These results provide insights into how weed harmfulness may be linked to species-specific strategies and may vary depending on the environmental context, supporting the idea of more targeted, trait-informed weed management strategies in cropping systems.