Time of Day Effects on Photosystem II



Various times of day have different effects on plant efficiency. Specifically, different times of day represent distinct positions and intensities of sunlight on plants. Inside plant leaves, chloroplasts convert light energy into usable plant energy via photosynthesis. According to Dodd (et al., 2005), the conversion of light energy to chemical energy is related to circadian clocks and differs at different times in the day. The MultispeQ v1.0 device, produced by Professor David Kramer at Michigan State University is used to measure many aspects of plant productivity. Dr. Kramer This study focuses on the efficiency of the photosystems at varying times of the day. The MultispeQ v1.0 measures the linear electron flow (LEF), efficiency of photosystem II (ΦII), and relative chlorophyll content (SPAD). The goal of this study is to determine if the different times of day have a relationship with the photosystem II efficiency and linear electron flow. Previous research (Zerevoudakis et al., 2012) shows that during the evening, when there is less direct sunlight, the photosystem efficiency will be greater rather than earlier in the day when the plant is receiving direct sunlight. It is also assumed that the linear electron flow will have decreased throughout the day, to the time of the evening measurement. A similar study was done at MSU while using the MultispeQ devices. The study showed how time of day had effected LEF values. Findings showed that LEF values are higher in the evening than in the middle of the day (Stephens et. al 2016). This will help farmers determine the best time of day to apply supplements or herbicide to their crops. The photosystems are more active when there is less direct sunlight, it is best to apply the supplements at these times.


To collect data, a MultispeQ v1.0 device was used and paired with an Android tablet. To use the MultispeQ device, the top of the device showing the light sensor was held facing in an upward direction while a leaf was placed within the measurement opening and the clamp was shut over the leaf. The MultispeQ device then took approximately 15 seconds to measure the various aspects of plant health. Some elements that were measured were the efficiency of photosystem II(ΦII), linear electron flow (LEF) and relative chlorophyll levels (SPAD). This measurement procedure was repeated 180 times each measurement day. 90 measurements were collected in the afternoon time (12pm- 3pm) and another 90 measurements were collected in the evening (6pm-9pm) over six days. Six Syringa vulgaris (Lilac) plants were studied to cover a broad sample and limit chances for error. These plants were planted on MSU’s campus in 1993. Each bush was divided into three sections; north, south and top. From each third of the bush, five leaves were randomly chosen and one measurement was taken from each leaf. Statistical analyses were done using a one-way ANOVA to compare differences between each section of bush (north, south and top) and another ANOVA test was used to compare differences between the bushes.


Leaf Photosynthesis MultispeQ V1.0


Measures many photosynthesis-related parameters in <15 seconds, including:

  • Chlorophll Fluorescence: Phi2, PhiNPQ, PhiNO, NPQt, qL, LEF
  • Relative Chlorophyll: SPAD
  • Proton Motive Force: ECSt, vH+, gH+
  • Absorbance at: 450, 535, 605, 650, 730, 850, 880, and 940nm.
  • Leaf Thickness (in mm), angle, and cardinal direct...


  1. Lilac Bush # (Multiple Choice)
  2. Quadrant of bush (Multiple Choice)
  3. Leaf # (Multiple Choice)



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