Abstract
Understanding environmental factors is essential to maximizing the biomass production of plants. There have been many studies on the effects of the photosynthetic photon flux (PPF), photoperiod and air temperature as separate factors affecting plants, including under a closed transplant production system (CTPS). However, few studies have investigated the combined effects of these factors on plant growth. Germinated tomato and red pepper seedlings were transferred to three different photoperiods with five different photosynthetic photon fluxes (PPFs) at an air temperature of 25/20 °C to investigate plant growth under a different daily light integral (DLI). Three different air temperatures, 23/20, 25/20, and 27/20 °C (photo/dark periods), with five different PPFs were used to examine plant growth under different DIFs (difference between the day and night temperature). Increasing the DLI from 4.32 to 21.60 mol·m−2·d−1, either by increasing the photoperiod or PPF, improved the growth of seedlings in both cultivars. However, when comparing treatments that provided the same DLI, tomato seedlings had s significantly higher growth when grown under longer photoperiods and s lower PPF. Even in higher DLI conditions, reduced growth due to higher PPF indicated that excessive light energy was a limiting factor. At 23 and 25 °C, tomato seedlings showed similar correlation curves between growth and PPF. However, at the higher temperature of 27 °C, while the slope of the curve at low PPFs was similar to that of the curves at lower temperatures, the slope at high PPFs was flatter. On the other hand, red pepper seedlings displayed the same correlation curve between growth and PPF at all tested temperatures, and red pepper plants accumulated more dry weight even at higher temperatures. These results suggested that the combination effect was more useful to observe these overall tendencies, especially in reacting to a second factor. This will provide us with more information and a deeper understanding of plant characteristics and how they will behave under changing environments.
Highlights
Plant factories have become more popular in the cultivation and production of vegetable seedlings [1], herbs [2], and medicinal plants [3,4] due to their numerous advantages over conventional protected horticulture
The shoot length of tomato and red pepper was the highest at 200 μmol·m−2·s−1 (DLI 8.64 for 12 h·d−1, 11.52 for 16 h·d−1, and 14.40 mol·m−2·d−1 for 20 h·d−1) and decreased under higher photosynthetic photon flux (PPF) treatments (Figure 4). This result agrees with a previous study, in which the hypocotyl length of lettuce decreased as the daily light integral (DLI) increased from 5.8 to 25.9 mol·m−2·d−1
The results of this study highlight the differences in nature between tomato and pepper, as well as the complex interactions among PPF, photoperiod, and temperature on the growth and morphology of plants
Summary
Plant factories have become more popular in the cultivation and production of vegetable seedlings [1], herbs [2], and medicinal plants [3,4] due to their numerous advantages over conventional protected horticulture. In transplant production, closed systems using artificial lighting, which are called closed transplant production systems (CTPSs), have been designed and adopted for the cultivation and propagation of seedlings and transplants [5]. These systems can reduce labor and resource consumption [6], increase the production curve, and improve plant quality due to the ability to control environmental factors for optimal growth conditions without being affected by outside weather [5]. Air temperature affects transpiration, morphology, and photosynthetic efficiency [10,11,12] Together, these factors have a great impact on plant growth and quality. It is essential to understand how plants respond to changes in these factors for successful CTPS operation
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