Evaluating the canopy light environment, photosynthesis, and fruit comprehensive performance of greenhouse tomato under different mechanized planting layouts

Plant layout is critical for the formation of canopy microenvironment, and fruit yield and quality. Plant-layout designs that meet the requirements of photosynthetically efficient and mechanizable greenhouse cultivation are urgently needed. Here, we report our findings from a two-year trial using tomatoes grown in a plastic film greenhouse at high planting density (HPD, 4.55 plants · m−2) or low planting density (LPD, 3.13 plants · m−2). Each density comprised south-north (SN) and east-west (EW) row orientations, with three plant layouts (S1–S3 or E1-E3, S and E represent SN and EW row orientations, respectively) in each orientation: 90 cm + 35 cm + 35 cm, 90 cm + 60 cm + 30 cm, and 90 cm + 90 cm + 25 cm for HPD; and 120 cm + 40 cm + 40 cm, 120 cm + 60 cm + 36 cm, and 120 cm + 120 cm + 27 cm for LPD. Analysis included canopy accumulated light absorption (ACL), photosynthesis (ACP), and light uniformity (UCLP) conducted using a three-dimensional canopy photosynthesis model, along with individual fruit indices, and a comprehensive evaluation using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). Plants grown under S2 and E2 exhibited respective dominance in both planting densities compared to those grown under any other treatment. Particularly, S2 showed higher ACL and single fruit weight, whereas E2 showed superior UCLP, comprehensive fruit quality, and fruit uniformity. Therefore, E2 was identified as an optimal plant configuration for both HPD and LPD based on overall fruit performance as evaluated using the TOPSIS method. Correlation analysis indicated that the light environment of the lower canopy layer under HPD and that of the middle canopy layer under LPD showed the strongest correlations with the main fruit indices. Overall, the optimal plant layout identified herein provides valuable decision support for horticultural production under mechanized planting conditions. The correlations between canopy light and fruit indices define quantitative breeding and management targets for optimizing fruit performance through adjustments in plant structure.