Abstract: 【Objective】The present study investigates the impacts of different light intensities on leaf water potential, hydraulic conductivity, and photosynthetic characteristics of soybean at the seedling stage. In addition, the adaptation mechanisms of leaf vein traits in response to variation in light intensities have been found to provide theoretical support for improving light energy utilization in soybean in the future.【Method】Two soybean cultivars‘Nandou 12’ (shade-tolerant) and‘Guixia 7’ (shade-sensitive) were grown and placed in growth chambers where the plants were subjected to different light treatments as high light intensity  (424.47±12.32 µmol·m^-2·s^-1, HL), medium light intensity (162.52±20.31 µmol·m^-2·s^-1, ML) and low light intensity (93.93±9.87µmol·m^-2·s^-1, LL). The effects of different growth light intensities on hydraulic conductance, photosynthetic parameters, leaf water potential and leaf vein traits in seedling soybean leaves were studied after 20 days of treatment.【Result】The results of present study revealed that LL treatment significantly impacted the leaf hydraulic conductance of both soybean cultivars, and the leaf hydraulic conductance of Nandou 12 was significantly higher than that of Guixia 7 under all three treatments. The treatment ML and LL reduced the leaf hydraulic conductance of Nandou 12 by 7.56% and 21.24%, net photosynthetic rate by 29.44% and 46.49%, and stomatal conductance by 43.96% and 58.89% over the HL, respectively. Similarly, the leaf hydraulic conductance of Guixia 7 was reduced by 42.16% and 23.71%, stomatal conductance by 54.55% and 45.79%, and net photosynthetic rate by 37.03% and 42.06% under ML and LL treatment, respectively. Moreover, no significant differences in leaf water potential of both cultivars were found among different treatments. Leaf hydraulic conductance and stomatal conductance of soybean reached a highly significant positive correlation (P＜0.01) with three light intensity treatments. A positive correlation of leaf hydraulic conductance with net photosynthetic rate (P＜0.05) and stomatal conductance (P＜0.01) were observed as the light intensity decreased. On the other hand, the minor leaf vein density and area of xylem conduits of major and minor veins were considerably reduced under ML and LL in both soybean cultivars. The minor leaf vein density and area of xylem conduits of major vein were significantly higher in Nandou 12 over the Guixia 7 under ML and LL treatments. The major leaf vein density of Nandou 12 did not change significantly between treatments, and that of Guixia 7 was significantly reduced by 11.4% and 15% under ML and LL treatments compared to HL. A decrease in the light intensity significantly increased the distance between leaf vein and stomata. The treatment ML and LL increased the distance between vein and stomata by 21.33% and 60.01% for Nandou 12 and by 31.50% and 53.59% for Guixia 7 as compared to HL treatment. Correlation analyses showed that hydraulic conductance of soybean leaves was significantly positively correlated (P＜0.05) with the density of minor leaf veins, area of xylem conduits of major and minor veins, and negatively correlated (P＜0.01) with the distance between vain and stomata.【Conclusion】Light intensity affects leaf hydraulic conductance by regulating the leaf vein structure of soybean. Low light reduces leaf hydraulic conductance in soybean, but leaf hydraulic conductance and stomatal conductance remain coordinated to maintain a balance between leaf water supply and demand as light intensity decreases. Having a higher vein density under low light can shorten the distance of water transport and ensure a better leaf water supply capacity, thus facilitating CO₂ diffusion and photosynthesis, which is another strategy for shade-tolerant soybean to adapt to a low-light environment.

Key words: soybean, leaf hydraulic conductivity, stomatal conductance, light intensity, leaf vein