Short light/dark cycles favour photosynthetic efficiency and growth in grapevines

Climate change and the expansion of the urban frontier pose a threat to the sustainability of agricultural systems. In this context, confined cultivation systems can provide a viable alternative for maintaining consistent production levels. Light and temperature in greenhouses or growth chambers are major regulatory factors in plant functioning, which can be easily modulated. Shortening the photo-/nycti-periods, compared to the standard cycle (12 h light/12 h dark), has been shown to enhance the photosynthetic activity and growth in annual crops, but its effect on perennial crops such as grapevines remains unexplored. This study aimed to describe the effects of accelerating the light/dark cycle to a repeated short pattern (3 h light/3 h dark, ‘T3/3’), in contrast to the circadian-aligned regime (12 h light/12 h dark, ‘T12/12’) while keeping the same temperature and photosynthetic active radiation amounts per day. We evaluated photosynthetic efficiency, leaf growth, biomass production and partitioning, and resource use efficiency (water and light). T3/3 in both genotypes maintained stable net photosynthetic rates (An) and high photosystem II efficiency (φPSII) during the light cycle, avoiding the 62 % drop observed under T12/12 after 3 h of exposure. In addition, the dark respiration (Rd) was reduced for T3/3 (–51 %) compared to T12/12, leading to a higher daily carbon gain (+66 %) for T3/3. Short light/dark cycle also increased total leaf area (LA) in both genotypes, due to a higher initial rate of leaf expansion (+52 %), and extended the duration of the vegetative phase (P1) by seven days compared to T12/12. However, the duration of the ripening period (P2) and total dry mass (DMtotal) did not show any differences between treatments and were mainly determined by genotypic variability. GENOT 102 showed a tendency to prioritise biomass partitioning to the reproductive organ and also produced more DMtotal (+38 %) compared to GENOT 16. Lastly, the efficiency in the use of resources (light and water) over the cycle was similar, regardless of the treatments and genotypes. These findings lay the foundation for adjusting light/dark cycles and genotype selection to maximise productivity and sustainability in confined growing environments.