Drip irrigation can improve the absorption, transfer and fixation of light energy in soybean under heavy metal stress

Excessive heavy metals can limit plant photosynthesis. To explore drip irrigation's impact on soybean photosynthesis under soil heavy metal stress, this study conducted four drip irrigation experiments (D1 to D4) by controlling the soil matrix potential lower limits at −10, −20, −30, and −40 kPa, respectively. A comprehensive analysis was conducted on the impact of drip irrigation on soybean spectral characteristics, chlorophyll fluorescence, photosynthetic characteristics, growth, and yield under combined Cd, Pb, and Cr(VI) stress. The results show that (i) Drip irrigation increased soybean leaf area and photosynthetic pigment content under heavy metal stress, alleviated the damage of heavy metal to chloroplasts, and enhanced the light energy capture and absorption capacity. Among them, D1 and D2 had a better effect on the red light absorption of leaves. (ii) Drip irrigation improved the ability of leaves to convert light energy into chemical energy and electron transfer rate, enhanced the utilization efficiency of light energy and the high light tolerance in leaves, thus promoting the transfer of light energy in soybean under heavy metal stress. (iii) D1 and D2 significantly increased the net photosynthetic rate and light saturation point, thus promoted the fixation of light energy, and the seed weight was increased by 157.79 % and 147.86 % compared with surface irrigation in 2023, respectively. In summary, drip irrigation notably improved soybean photosynthesis under heavy metal stress, advancing the theoretical framework for drip irrigation applications in heavy metal-polluted soils. • Heavy metal (HM) stress inhibited soybean photosynthesis. • Drip irrigation enhanced soybean light harvesting under HM stress. • Drip irrigation alleviated the damage of HMs to chloroplast structure. • Drip irrigation improved soybean light-use efficiency and phototolerance. • Drip irrigation improved soybean growth and yield under HM stress.