Integrated biomarker responses of rice associated with grain yield in copper-contaminated soil

Copper (Cu) contamination in soil is an environmental issue that affects rice growth and development. This study investigated changes in photosynthetic capacities in combination with integrated biomarker responses at different growth stages of rice (Oryza sativa L. var. Hom Bai Toey) exposed to various concentrations of Cu. A randomized complete block design with four replications was used. Exposure to high copper concentrations of 200 Cu mg kg^-1 of soil and more resulted in a marked decline in the photosynthetic efficiency of Photosystem II (Phi2) but increased yield of non-photochemical quenching (PhiNPQ) and yield of non-regulatory energy dissipation (PhiNO) at tillering and flowering stages. In addition, these concentrations induced a delay in the flowering of rice, as a consequence of stress experienced in early growth stage. Significant lipid peroxidation and leaf area reduction were observed with 400 Cu mg kg^-1 treatment at flowering stage. Rice grain yield decreased significantly at copper concentrations of 200 and 400 mg kg^-1. Overall, excess copper inhibited photosynthetic capacity, growth, and development of rice in the early growth stage, and synergistic effects of yield components contributed to final grain yield reduction at harvesting stage. In addition, calculated integrated biomarker response (IBR) values reflect well the severity of Cu toxicity with a decreasing order from tillering stage to harvesting stage.