Abstract
This study investigated the effects of daily light integral (DLI) on the photosynthesis, growth, and flowering of Veronica rotunda var. subintegra and V. longifolia. Six-week-old seedlings with four or five nodes were grown under five average DLI levels (3.6, 6.6, 8.1, 14.7, and 18.3 mol m−2 d−1) in a greenhouse. Both species grown under DLI conditions of over 8.1 mol m−2 d−1 showed a lower maximum quantum efficiency (Fv/Fm) than those grown under DLI conditions of 3.6 and 6.6 mol m−2 d−1 after 2 weeks of treatment. However, these differences diminished after 6 weeks of treatment. In the light response curve, the net CO2 assimilation rates (An) for light intensities of 200–1200 μmol m−2 s−1 increased with increasing DLI. Most growth parameters, including plant height, number of branches, stem diameter, and chlorophyll contents of both species, were promoted with increasing DLI. Although increasing DLI did not affect the percent flowering in either species, the number of nodes below the first inflorescence was lower under higher DLI conditions. The number of visible inflorescences (VIs) and inflorescence length of the first open flower showed similar trends as the growth parameters. The parameters associated with days to flowering were shortened as DLI increased. These results suggest that high DLI conditions could promote the growth and flowering of two Veronica species by increasing An and that they can be used to force flowering of these plants in commercial production.