Abstract:

The purpose is to determine the causes of canopy leaf turning and the effect on grain weight. 28 soybean cultivars were used as materials in the field experiment. The relationship between leaf area, specific leaf weight, leaf shape index, water content and the rate of canopy leaf turning of the top 4 leaves at the early seed-filling stage was studied by random block design. The differences between leaf turning and the net photosynthetic rate, 100-grain weight and grain weights were compared. The results showed that the rate of canopy leaf turning of different soybean varieties was 0-26.5%, which was significant, and the rate of canopy leaf turning of ‘zhonghuang 31’, ‘zhonghuang 42’ and ‘zhonghuang 13’ were the highest. The area of single leaf was 46-151 cm², and that of ‘zhonghuang39’, ‘zhonghuang 42’ and ‘zhonghuang 13’ were the largest. Specific leaf weight was 0.536-1.64 mg/cm², among which, that of ‘zhonghuang 322’, ‘zhonghuang 313’and ‘zhonghuang 13’ were the lowest. The leaf shape index was 1.35-3.51, among which, that of ‘zhonghuang 70’, ‘zhonghuang 80’ and ‘zhonghuang 42’ were the lowest. The tested soybean varieties were divided into three groups. Group I had smaller single leaf area, higher leaf weight and larger leaf shape index, and the rate of leaf turning was 1.03%. Group III varieties had larger single leaf area and smaller leaf weight, and the rate of leaf turning was up to 19.7%. There were four species in group II, with leaf area, specific leaf weight, leaf shape index and the rate of leaf turning all between those of group I and group III. After leaf turning, the net photosynthetic rate was significantly reduced, with an average decrease of 31.7%. The 100-grain weight of ‘Xindadou27’ with more grains decreased by 10.38%-22.4%, while the grain weight of ‘Jiyu60’ with fewer grains did not decrease. The upper leaves of soybean with higher rate of reversing leaf were more observed in leaves with larger single leaf area, smaller specific leaf weight and lower leaf shape index, this could reduce the net photosynthetic rate of leaves and thus cut down the same-node and single-node grain weight, and is not conducive to the high yield of soybean.

Key words: soybean, leaf turnover, leaf area, net photosynthetic rate, grain weight