Growth and Photosynthetic Capacity of Basil Grown for Indoor Gardening under Constant or Increasing Daily Light Integrals

In the quest to identify minimum daily light integrals (DLIs) that can sustain indoor gardening, we evaluated DLIs less than the recommended ranges for commercial production of basil ( Ocimum basilicum ). Experiments were conducted for 8 weeks to evaluate the effect of providing a constant vs. an increasing DLI over time (DLI Inc ) on growth and photosynthetic capacity of green (‘Genovese Compact’) and purple (‘Red Rubin’) basil grown hydroponically under a constant ambient temperature of 21 °C. Plants were grown under a 14 h·d –1 photoperiod and were subjected to the following DLI treatments: 4 (DLI 4 ), 6 (DLI 6 ), 8 (DLI 8 ), or 10 (DLI 10 ) mol·m –2 ·d ‒1 (80, 119, 159, and 197 µmol·m ‒2 ·s ‒1 , respectively); DLI Inc was used as a fifth treatment and was achieved by transitioning hydroponic systems systematically to treatments with greater DLIs every 2 weeks. In general, regardless of cultivar, leaf area, leaf number, and overall growth [shoot fresh weight (SFW) and shoot dry weight (SDW)] were similar for plants grown under DLI Inc to DLI 4 and DLI 6 during weeks 2, 4, and 6. However, plants grown under DLI Inc produced the same leaf area as those grown under DLI 10 at week 8. Nonetheless, across weeks, growth was significantly less under DLI Inc compared with DLI 10 , but similar to that produced by DLI 8 at week 8. Photosynthetic responses were significant only at week 8, for which leaves of plants grown under DLI 8 , DLI 10 , and DLI Inc had 15% to 25% greater maximum gross carbon dioxide (CO 2 ) assimilation ( A max ) than plants grown under DLI 4 . The light saturation point of photosynthesis was unaffected by DLI, but showed a general increasing trend with greater DLIs. Overall, our results suggest that providing a constantly high DLI results in greater growth and yield than increasing the DLI over time. In addition, we found that changes in A max and the light saturation point are not good indicators of the capacity of whole plants to make use of the available light for photosynthesis and growth. Instead, morphological and developmental traits regulated by DLI during the initial stages of production are most likely responsible for the growth responses measured in our study.