Data from the Greenhouse: Photosynthetic Efficiency – Part 1

In greenhouse horticulture, data now plays a crucial role in optimizing cultivation conditions. By analyzing various metrics, such as photosynthetic efficiency (PE) and light intensity, growers can better understand how their crops respond to different environmental factors. In this article, we discuss the photosynthetic efficiency of Phalaenopsis during winter, based on data collected in MyLedgnd using a photosynthetic efficiency sensor and a PAR sensor.

Photosynthetic efficiency indicates how effectively a plant converts the light it receives into sugars, the energy source it needs to grow. This process is especially crucial during winter when less natural sunlight is available. The more efficiently a plant can convert light, the better it can build biomass and store energy. In this context, the greenhouse lamps become a vital source of light. In this example, we focus on Phalaenopsis.

A sensor measures the photosynthetic efficiency (PE) of the Phalaenopsis, while the PAR value indicates the amount of light falling on the plant. This data is displayed in a graph, with two lines providing us with valuable insights.

In the graph below (Graph 1), we observe two lines:

1. Photosynthetic efficiency (PE), measured by a sensor.
2. PAR values, which describe the amount of light reaching the crop.

Graph 1

The first notable moment is when the lamps are turned on at 8 a.m. (Graph 1, marker 1). Upon switching on the lamps, we observe a sharp drop in photosynthetic efficiency from 79% to 65% (Graph 1, marker 2). This is a normal phenomenon: when plants are suddenly exposed to increased light, they become less efficient at converting that light into sugars. This results in lower efficiency.

Graph 2

In the same graph above, we see that photosynthetic efficiency (PE) quickly stabilizes. PE remains around 65% for the rest of the day (Graph 2, marker 1), indicating that the plant, despite the lower efficiency, can consistently process the incoming light. This shows that the Phalaenopsis is not overwhelmed by the sudden increase in light.

Between approximately 11:00 a.m. and 3:00 p.m., something interesting occurs: the PAR line continues to rise, while the PE decreases further (Graph 2, marker 2). In other words, the more light the crop receives, the less efficiently the plant converts that light into sugars. This can be compared to a car engine: the faster you drive, the more fuel you consume. Similarly, the plant has to work harder as it receives too much light, resulting in lower efficiency.

Graph 3

Around 4:00 p.m., Graph 3 shows in the yellow PAR line that light intensity remains stable until approximately 8:30 p.m. The LED lighting provides a consistent light level of around 40 micromoles. The crop is exposed to a constant amount of light. However, based on the data, we observe an intriguing phenomenon: photosynthetic efficiency gradually declines (Graph 3, marker 1).

This suggests that the Phalaenopsis might be depleting its malate reserves. Malate is a compound stored by the plant at night and used during the day to support photosynthesis. When the malate reserves are exhausted, the plant can no longer maintain the same photosynthetic efficiency, even under stable light conditions.

Malate, also known as malic acid, is an organic acid that plays a crucial role in plant metabolism. In orchids such as Phalaenopsis, the stomata remain closed during the day to minimize water loss. During this time, the plant relies on its nighttime malate reserves, which are converted into CO₂ to sustain photosynthesis. At night, the stomata absorb CO₂, which is converted into malate and serves as a carbon source during the day. When the malate reserves are depleted, the plant no longer has access to CO₂ for producing sugars through photosynthesis.

Currently, the greenhouse lamps are turned on at around 8:00 a.m. and remain on until 7:30 p.m. During this period, the Phalaenopsis receives a constant light intensity of approximately 40 µmol, which is sufficient to provide the plant with the necessary light during winter. However, the current strategy appears to overlook the potential to improve energy efficiency by optimizing the plant’s use of its malate reserves.

Consider gradually dimming the greenhouse lamps starting at around 5:00 p.m. The plant demonstrates reduced efficiency in utilizing light as early as 4:30 p.m. Dimming the lights saves energy without significantly impacting the plant’s photosynthetic capacity, as the plant is already less efficient at converting light into sugars during this period.

By gradually dimming the lights, growers can not only reduce energy consumption but also place less strain on the plant. Over the long term, this approach will contribute to healthier cultivation. This strategy is particularly important during winter, when energy usage in greenhouses is high due to the additional lighting required to compensate for the lack of natural sunlight.

The photosynthetic efficiency of the Phalaenopsis during the winter months is a complex process, heavily influenced by the available light intensity and the plant’s malate reserves. By leveraging greenhouse data in MyLedgnd, growers can gain deeper insights into how their crops respond to varying light levels and adjust their strategies accordingly for optimal growth and energy efficiency.