Abstract
Although open-central canopy (OCC) is popular in apple (Malus × domestica) orchards in Loess Plateau of China, its relevant photosynthetic mechanisms have not been elucidated. In this study, changes in photosynthetically active radiation (PAR), gas exchange, chlorophyll fluorescence quenching and fruit quality in apple trees were measured in OCC and compared with those in the conventional condensed round and large canopy (RLC). Results showed that light intercepted at different orientations was 44% higher by OCC than that by RLC. The improved light environment within OCC remarkably increased leaf maximum net photosynthetic rate (Pnmax) and significantly decreased stomatal limitation. Under high light, the ratio of photorespiratory rate to gross photosynthetic rate (Pr/Pg) in OCC was higher than that in RLC. Moreover, reversible component in non-photochemical quenching (r(qE)) was increased, while irreversible component (r(qI)) was decreased in OCC than in RLC. As a result, the fruit quality in OCC was greatly boosted as evidenced by the significantly increased single fruit weight, fruit flesh firmness and fruit soluble solid contents and the sharply decreased fruit titratable acid contents. PAR intercepted by the canopy and the fruit soluble solid contents, leaf Pnmax or single fruit weight were positively correlated, while PAR or Pnmax was negatively correlated with the fruit titratable acid contents. Accordingly, the improved crown light environment and the enhanced leaf photosynthetic performance and photoprotective capacity in OCC led to the boosted fruit quality.
