Photosynthetically active radiation and photosynthetic physiological characteristics of leaves within the canopy were heterogeneous. The response to row spacing and irrigation amount of light interception and photosynthetic capacity of leaves in different parts of tomato canopy were explored in this study. The effects of row spacing and irrigation amount on photosynthetic productivity of tomato canopy were studied in detail, and the comprehensive quality of fruit was analyzed, which provided a theoretical basis for the setting of row spacing and irrigation amount in mechanized cultivation of tomato.

Tomato, the test material, was cultivated in a wide and narrow row, with plant spacing of 35 cm. Small row spacing of 40 cm, and three large row spacing levels were set: 70 cm (P1), 120 cm (P2), and 170 cm (P3). Two irrigation levels were set: conventional irrigation (W1) and light deficit irrigation (W2). The experiment was a full factorial experiment with 6 treatments. The leaf area and light interception amount of each leaf position were measured. The canopy was divided into six parts, and the net photosynthetic rate (Pn), leaf mass per area (LMA), chlorophyll (Chl) and N, P, K content were measured. The canopy photosynthetic capacity under each treatment was comprehensively analyzed by taking the proportion of leaf area of each part to that of the whole plant or the proportion of leaf dry weight of each part to that of the whole plant as weights. The correlation of each index was analyzed by the Pearson correlation coefficient. The dry and fresh weight, yield per plant and fruit quality of the second ear were measured. The comprehensive quality of tomato was evaluated and ranked by PCA method and combined weighting-TOPSIS method based on game theory.

The effects of increasing row spacing on canopy leaf area, light interception and photosynthetic capacity were mainly reflected in the middle and lower parts of the canopy. The leaf area in the mid canopy increased first and then decreased with the increase of the row spacing. The leaf area in the lower canopy and the light interception in the mid and lower canopy increased significantly from P1 to P2, but slightly increased from P2 to P3; the Pn in the mid and lower canopy showed that P2 increased by 8.06%-11.32% compared with P1, and P3 increased by 14.25%-24.40% compared with P2; the LMA showed that P2 increased by 1.31%-33.24% compared with P1, and P3 increased by 6.09%-17.86% compared with P2; the Chl content of P2 was 3.42%-6.81% higher than that of P1, and P3 was 3.19%-4.96% higher than that of P2; the N content of P2 was 13.89%-34.73% higher than that of P1, and P3 was 2.21%-19.74% higher than that of P2; the content of P and K had no obvious regularity. On the whole, the content of Pn, Chl and N increased with the increase of row spacing, and the LMA increased with the increase of row spacing under light deficit irrigation and showed P3>P1>P2 under conventional irrigation; under three row spacing levels, the LMA and N content under conventional irrigation were higher than those under light deficit irrigation, the Pn under conventional irrigation was higher than that under light deficit irrigation under P1 and P3, while the Pn under light deficiency irrigation was higher under P2; the Chl content under conventional irrigation was higher under P1, while the Chl content under light deficiency irrigation was higher under P2 and P3. With the increase of row spacing, the dry and fresh weight of the aboveground parts increased under conventional irrigation, and increased first and then decreased under light deficit irrigation; the aboveground dry and fresh weight of conventional irrigation was higher than that of light deficit irrigation. The yield per plant increased with the increase of row spacing under the two irrigation levels, and the increase from P1 to P2 was larger (compared with P1, P2 under conventional irrigation and light deficit irrigation increased by 33.75% and 24.32%, respectively.), while the yield per plant increased only slightly from P2 to P3 (compared with P2, P3 increased by 2.87% and 4.30% under conventional irrigation and light deficit irrigation, respectively.); the yield per plant under conventional irrigation was higher than that under light deficit irrigation. Increasing row spacing and reducing irrigation amount could optimize the comprehensive quality of fruit, and the top three comprehensive quality scores were P3W2, P2W2 and P3W1.

P3W1 was the highest in leaf Pn, LMA, N content, aboveground dry and fresh weight and yield per plant, and P3W2 was the highest in canopy light interception, Chl content and comprehensive quality score.